GREENHOUSES

IN

ALASKA

COOPERATIVE EXTENSION SERVICEUniversity of Alaska - Fairbanksand U.S. Department of Agriculture Cooperating

^Publication No. 51Reprint March 1981

Wayne Vandre, HorticulturistCooperative Extension Service

University of Alaska

This publication was originally developed in 1955 by C.H. Fahnestock, Alaska Agricultural Experiment Sta-tion, Palmer, with the title, "Greenhouses for Alaska," It was revised and expanded in 1958 by Dr, RichardFoley, Alaska Agricultural Experiment Station and edited by H.W. Pillsbury and A.M. Mick of the Universityof Alaska Extension Service, At that time the title was changed to "Planning and Managing Greenhouses inAlaska," In 1964 the publication was further revised by H.W. Pillsbury and C. Ivan Branton, Cooperative Exten-sion Service, University of Alaska. The title was shortened at that time to "Greenhouses in Alaska." In 1971the publication received a major revision with much new material added by Alan C. Epps and Axel R. Carlson,Cooperative Extension Service, University of Alaska. The publication was reprinted in 1973 and slightly revisedin 1977.2/77/131/351/ARS/ACEflOM

The University of Alaska's Cooperative I xtension Service programs are available to all, without regard to race,i olur, age, s(>x, (reed, or national origin

Issued in furtherance ol Cooperative Extension work, ails of May 8 and June 30, 1914, in cooperation with theU S Department of Agriculture, Dr lames W Matthews, Director, Cooperative Extension Service, University ofAlaska

TABLE OF CONTENTS

PageINTRODUCTION 1GREENHOUSE CONSTRUCTION 2

Framing 2Site Selection , 7Size 7General Construction Information 7Beds or Benches? , , 8Coverings , . 9Plastics 12Heating 13Snow Loads 15

PLANT ENVIRONMENT 15Lighting , . 15Ventilation 15Soil 15

FERTILIZERS . 16Manure 16

WATERING 17TRANSPLANTS 17

Raising Seedlings , 17Transplanting . 18

PLANT PROBLEMS 19Insect Pests 19Major Diseases 19

GREENHOUSE CROPS 22Tomatoes 22Tomato Troubles 24Cucumbers 25Snap Beans 26Peppers • 27Eggplants 27Lettuce 28Radishes 28Onions 28Sweet Corn . 29Muskmelons, Watermelons, & Winter Squash 29

PageAPPENDIX 30

Table A Heat Transmission Coefficients (C) of Common Building Materials . , 31Table B Efficiency of Heating Systems 31Table C Heating Value of Fuels 32Table D Heating Emission of Radiation 32Table E Fin-Tube Radiation Capacity Rating 33Table F Capacities of Typical Projection-Type Unit Heaters 34Table G An Example of Computing Greenhouse Heating Requirements . . . . 35Table H A Method of Computing Greenhouse Heating Requirements 36

Table 1 List of Greenhouse Plans 39Table J List of Greenhouse Publications 40

LIST OF FIGURES

Figure Page1 Posts and Beams 22 Clear Span Trusses 23 Rigid Frame 34 Two-pin Rigid Frame 35 Laminated Arches (Flat Lumber) 46 Laminated Arches (Flexible Lumber) 47 Lean-to Greenhouse 58 Sash-covered Greenhouse for Small Plants 69 Sealing 810 An Oil-or Gas-fired Ventilation System . 1311 Perforated Plastic Ducts for Air Distribution 1412 Damping-off in Tomato Seedling 2013 LeafMold 2014 Powdery Mildew 2115 Ground Beds , , , , , , , . . , 2216 How to Support and Prune Tomatoes 2317 How to Support and Prune Cucumbers 25

LIST OF TABLES

Table Page1 Plastic Greenhouse Coverings . . 102 Light and Heat Transmission Characteristics of Greenhouse Coverings . . . . . 103 Relative Heat Transmission Coefficients (U) of Greenhouse Coverings 114 Weight and Thickness of Typical Corrugated Plastic Sheets 11

INTRODUCTION

GREENHOUSES fit an Alaskan's way of living. They are valuable not only forvegetable production but for the satisfaction they provide the gardener.

While profits of greenhouse operators come chiefly from the pleasure of growingthings, the possibility of earning money should be considered. It is often the only chancethe neighbors have to buy garden plants and to get the best varieties of tomato andcucumber plants. Extra produce usually sells - especially if it has quality.

An ideal greenhouse provides maximum light penetration, is easily ventilated andadequately heated, and can be economically maintained. With the development ofpolyethylene film and other newer films resistant to ultra-violet light, the wood-framed,plastic greenhouse can be constructed by almost anyone handy with carpentry tools.Although ^a simple plastic greenhouse covered with polyethylene may initially beconstructed for less than one-third the cost of a glass greenhouse, it must be recoveredregularly. In constrast, a well-built metal-frame greenhouse covered with rigid,sunlight-resistant plastics and provided with adequate heating and ventilation systems maycost as much as a modern glass greenhouse.

Although wood-frame, plastic greenhouses are cheaper to build, they must beconstantly maintained and painted to resist deterioration. A double, plastic cover, whilemore expensive, will reduce condensation and maintenance. Galvanized steel or aluminumframed greenhouses require minimum maintenance but are more expensive. Light frame,plastic greenhouses require special considerations in areas of heavy snow, particularly inAlaska (as discussed under snow loads).

To simplify information, trade names of products have been used. No endorsement isintended, nor is criticism implied of similar products not named.

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GREENHOUSE CONSTRUCTION

FRAMING

Steel or aluminum framing is recommended for commercial growers. For the hobbygrower, lumber framing with lightweight, plastic covering performs very well. Frames forsuch greenhouses may be angular with a shed or gable roof, sloping or vertical side walls, andvertical end walls. The roof may be supported by posts and beams (Figure 1) or by clearspan trusses (Figure 2). Lumber rigid frames may be constructed of 2" x 4" or 2" x 6"members reinforced at corners with plywood gussets (Figure 3), Rigid framing is strongerwhen the wall frame is imbedded in concrete piers. This, however, necessitates the use oftreated wood. The two-pin frame may set on post-and-beam or heavy timber foundationsusing slightly heavier gussets (Figure 4).

Figure 1

Posts and Beams

Figure 2

Clear Span Trusses

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STAGING NAILS

1"x2"2"X2"2"X4"WIRE TIE-ON1"X2"

GUSSET

PLASTIC

PLASTIC

2"X4"

1"X2"1"X6"

GRAVELSLANT FORDRAINAGE12" POST HOLE

WITH POST INPOSITION ADD6 SAND 1 CEMENTWET WITH HOSE

Figure 3 Rigid Frame

STAGING NAILS

Figure 4 Two-pin Rigid Frame

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The roof and side walls may be curved and the end walls vertical. Curved rafters maybe laminated from flat pieces of lumber, as shown in Figure 5, to form arches. Also 1/2" x2" wood strips may be shaped over a form, which results in unbelievable strength when thestrips are nailed and glued onto 2" x 4" x 6" spacer blocks as illustrated in Figure 6,

3 - 2" x 12" PlankPlatform

Cut Board As In Detail H

Nailing Blocks4'-0" o.c.

Midwest Plan ServicePlan No. 72015

S A W E D R A F T E R J IG

Figure 5 Laminated Arches (Flat Lumber)

Figure 6

Laminated Arches (Flexible Lumber)

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Iron Pipe can be used for the framing of greenhouses. It is relatively cheap, small in size,easy to use, and lasts indefinitely if properly painted. Special fittings and clamps arenecessary to fasten the pipe together. They must be used because many of the joints cannotbe made by ordinary threaded pipe fittings. Threaded connections also tend to corrode andweaken when exposed to the humid atmosphere of a greenhouse for a long time.

The greenhouse may be constructed with shed roofs and supported from anotherbuilding (Figure 7). The gable or curved rafter house may be attached to another buildingfor tying into an existing heating system. Also they may be erected as independentstructures and provided with separate heating systems.

ExistingWall

. Ridge Vent2 x 3 Header

x 2 Vent Lever2x3 Rafters 24"O.G.

1/4x1 Strip Over Covering Materialon Each Rafter

^%^ 1 x 3 Cross-Tie

•2x3 Eave Plate

Side Vent

2 x 3 Side Posts 24"O.G.

Log, Concrete, Concrete Block,or Frame Foundation

Figure 7.—Local lumber and plastic covering can be used for this inexpensive lean-to greenhouse. A betterfoundation and a roof purlin would be necessary if glass were used for a covering material.

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The side walls may be very low to form a sash greenhouse with a shed or gable roof. Acribbed trench in the center will increase the head room for the operator (Figure 8). Thesash greenhouse is usually equipped with a removable sash that may be lifted for ventilationand stored when not in use. The sash may be glazed with glass or plastics.

Ridge Cap From 1 x 6 Lumber

1 x 5 Ridge Plate

Storm or Hotbed Sash

2x4 Sash Bar Spaced toFit Sash

4x4 Plate-Not Needed

Ground

Level

" \e 01 sasn

\

Avaiiaoie

«— 18" -*

\ Retaining Wall-^-— Extend to

| '

-May IBottoi

" If Logs Are Used

•* . Foundation of Logs, Concrete,Concrete Block, or Frame

te Necessary Tom of Aisle

oFigure 8.— Sash-covered greenhouse for small plants. If sidewalk are added, larger plants

may be grown. It is ventilated by openings in the ends or by raising several ofthe sash.

Roof slope of an Alaskan greenhouse should be as steep as is practicable. In early spring andlate fall the sun is low in the sky so that a roof with good slope transmits more of the sun'srays to the plants. In midsummer when the sun is high in the sky, a roof with a steep slopereflects more sunlight away from the interior and less heat is generated. Roofs with a 30- to45- degree slope are best. With a steep roof, moisture condensed on the inside tends to rundown rather than drip on the plants.

A list of where detailed plans may be obtained is provided in the appendix. Table I.

CAUTION must be used in adapting any of these plans to Alaska. Special steps must betaken to support heavier snow loads, as discussed later.

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SITE SELECTION

Several factors should be considered in selection of a greenhouse site. In general, thegreenhouse should not be shaded by trees or buildings but should be sheltered to preventwind damage and heat loss. A convenient, well drained site near heat, water and electricity isbest.

For best results the ridgepole should run east and west. Every lot, homesite andhomestead presents an individual problem and ingenuity may be needed. Greenhouses havebeen built on roofs to overcome shading or lack of space. No opportunity should beoverlooked.

Light is affected by the site, the covering on the greenhouse and the size of the framingmaterial. Avoid anything that cuts down the natural light.

Temperature is controlled by the heating equipment, the tightness of the structure, andthe covering material. Greenhouse vegetable crops usually require a temperature of 70 to 80degrees during the day and not lower than 60 at night. A reasonably stable temperatureshould be maintained.

Water in the soil and moisture in the air are extremely important. The amount of waterin the soil not only affects plant growth but may influence diseases and insect damage. Airmoisture also affects water lost from the soil by evaporation and transpiration.

Ventilation, the exchange of air inside and outside the greenhouse, provides fresh airfor the plants and controls temperature and humidity. These factors influence plant growthand make the difference between success and failure.

SIZE

No definite size can be given as best for a greenhouse. Most Alaskan greenhouses arethe product of the owner's imagination and skill. Many houses have been too small and toopoorly constructed to be efficiently operated.

Size should be based on the size of the family, the number of different crops onewishes to grow, and whether all the greenhouse produce is to be eaten fresh, canned, or sold.

Wood Preservation, Painting, and Glazing: Excessive moisture combined with warmth maycause rapid deterioration of wood. Wooden posts, wall planks, and benches which are incontact with the ground should be treated with a good wood preservative. Water solutionsof copper, chromium, and zinc are generally suitable preservatives. Many of the commonlyused preservatives such as creosote and pentachlorophenol are toxic to plants and shouldnot be used. Unless you are familiar with wood preservatives, obtain full information fromyour Extension Service agent or obtain one of the preservatives especially formulated forgreenhouses. These will not harm your plants and can be used under ordinary paint.

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Above-ground wooden parts, (except benches) should be painted, as soon asconstruction is completed. Greenhouse paint should be high quality, light colored, and x-*vhighly reflective of light. Aluminum paint is best for wood and metal parts. Zinc and lead \^Jpaints are satisfactory.

Glass should be embedded in glazing compound with an overlap of one-fourth inch toprevent air and water leakage. A lap greater than this would be likely to cause breakage fromfreezing of moisture between the panes. Glass should be secured in place with glazing nailsor clips. It is best to apply one coat of paint to the sash before glazing and a second coatafter glazing.

Foundations: The foundation wall may be poured concrete, concrete block, stone, or wood,depending upon the intended life of the greenhouse, funds available, and soil conditions. Amasonry foundation is recommended for any permanent structure although a treatedwooden foundation is cheaper and should last five to ten years or longer. See Figure 9 fordetails of sealing a pole frame foundation.

BOTTOM PLATE TO BE 3"ABOVE GROUND LINE

90 LB. ROLL ROOFINGOR GALVANIZED IRON

SOILLINE

Figure 9,— This drawing shows a f Nmethod of sealing between V^the bottom plate and theground to prevent rotting.

The foundation must tie the greenhouse to the ground as well as support the weight ofthe structure. The weight of snow and ice and the force and direction of the wind must beconsidered. Foundations for permanent houses should extend below frost level or at least toa solid footing so that the house does not settle or heave.

BEDS OR BENCHES?

Greenhouse crops can be raised in either ground beds or in benches. Ground beds leavemore space for plants because of additional vertical height provided,and only a single narrowwalk is needed through the center. Beds allow use of wheelbarrows and garden tractors,because the whole floor space is clear until the transplants are set. If the plants are set onridges with furrows between them, watering can be done by flooding the furrows as needed.Ground beds allow the use of larger growing varieties, which tend to yield heavier crops.

On cold, wet soil or on permafrost, benches will probably have to be used. Bencheswarm up faster in the spring and permit an early start with transplants. The plants are higherand easier to care for. Also if over-fertilization occurs, it is easy to leach out the excessfertilizer by flooding the soil with water.

Disadvantages are generally encountered when tall crops such as tomatoes, cucumbers,and pole beans are grown. Starting the plant above the floor level reduces vertical growthspace. They either have to be cut off too short for a full crop or trained up into the peak ofthe house. This requires the use of a step ladder to prune, pollinate blossoms and harvest.

Benches also increase the initial cost of the greenhouse. They have to be replacedperiodically. More area is required because there is less soil per plant in benches. Becauseaisles must be left between benches there is more wasted space with the bench system. Inorder to reach the plants, benches can be only five feet wide if there is an aisle on each side,or two and one-half feet if there is an aisle on only one side.

Benches for growing large plants should be placed down close to the floor and shouldcontain at least eight inches of soil. Twelve inches is better.

Use ground beds where possible. If benches are desired only for starting plants, buildthem so that they can be removed when the plants are ready to set. In some cases, acombination of ground beds and benches is satisfactory.

Individual containers such as cans or pots can be used with either ground benches orbeds. They are especially useful for ornamental plants which you may want to move around.However, they require more labor to prepare the soil and fertilizer for planting, they aredifficult to water, and they are not readily adapted to most vegetables.

COVERINGS

Two types of coverings are in general use - glass and plastics. Glass is the traditionalcovering; although permanent, it is heavy to ship and requires heavier framing. Sometimesthe coverings are combined - using glass on the walls and plastics on the roof. The relativecosts and life of various types of coverings are shown in Table 1. The light and heatcharacteristics of coverings are shown in Table 2. The heat transmission coefficients(U-values) for various coverings are shown in Table 3, which includes the effect of surfacefilms and air spaces.

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TABLE 1 PLASTIC GREENHOUSE COVERINGS

Type

GlassPolyethylene

UV - inhibatorPolyvinyl Chloride Sheet

Sheet UV - inhibatorRigid

Polyester (Mylar)Rigid Fiberglass

Thickness

DS1 -8 mil

4 - 6 mil8 -12 milCorrugated3 - 5 mil4 - 8 oz/S.F,

Life

Infinite1 - 2 yrs,2 - 4 yrs.1 -2 yrs.4 + yrs.10 + yrs.7 + yrs.10 -20 yrs.

RelativeCost/SJF,*

551-22-33-101312-1512-1422-47

*Cents/Sq. Ft.

o

TABLE 2 LIGHT AND HEAT TRANSMISSION CHARACTERISTICSOF GREENHOUSE COVERINGS O

Film

PolyethylenePolyvinyl ChloridePolyvinylPolyesterFiberglass (Clear)GlassWater

Thicknessmils

21334

125125

2

Visible Lighttransmission

Percent

87878888

80-909096

Transparent toUltraviolet Infared

yesslightyesnoslightnoyes

yesnoslightslightintermediatenono

Jour. Agr. Eng. Res. 3(4): 281 - 287, 1958

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TABLE 3 RELATIVE HEAT TRANSMISSION COEFFICIENTS (U)OF GREENHOUSE COVERINGS

BTU/Hr/QF/SF1/

Type of Material Single Double

Glass

Polyethylene

Tedlar (polyvinyl fluoride)

Teflon (fluorinated ethylene propylene)

Mylar (polyester)

Fiberglass (acrylic)

1,13

1.60

1.30

1.25

1.05

.95

.89

.84-

.60

.67-

.65-

.74

.90

,70

,70

11 Air film and air space coefficients are included values based on 15 mph wind.

Corrugated plastic sheets are available in several weights and thicknesses, Table 4. Theheavier plastics should be selected for the roof. The sheets may be reinforced with strands ofglass or nylon to increase the structural strength. Films such as polyethylene, mylar, etc. areusually available in various thicknesses measured in mils (1 mil = 0.001 inch), from 2 to 10mils. A minimum of 6-mil thickness is recommended for greenhouse coverings.

Weight Thickness(oz,/sq.ft.) (inches)

4.00 .0304.20 .0325.00 .0376.00 .045

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PLASTICS

Many types of plastics are available for use in greenhouses including acrylics, polyvinylchlorides, polyethylene, polypropylenes, styrenes, and urethane.

Acrylics are the first and one of the few truly weatherproof groups of thermoplasticssuitable for greenhouse coverings. They exhibit almost complete weather resistance andcolorability or optical clarity where needed. On the other hand, however, they can becomebrittle, particularly in cold weather, and will ignite readily and support combustion. Bothflat and corrugated sheets which are reinforced with strands of glass or nylon are moreresistant to cold weather.

Vinyls are the lowest in cost of the various thermoplastics, Polyvinyl chloride, one ofthe oldest of the thermoplastics, is certainly the most versatile. Having inherently lowflame-spread and being usually self-extinguishing, it is now available in corrugated formsuitable for greenhouse construction. The newer polyvinyl fluorides are also now availablefor greenhouse construction,

Olefin thermoplastics are available as polyethylene or polyproplenes. Polyethylene canbe extended in flexible films of controlled thickness. Although it is initially least expensivefor greenhouse covering, in cold temperatures it tends to become rigid and inflexible. Inaddition, it exhibits considerable elastic creep and plastic flow or "set" under load and has atendency to fail at creases where folded in packaging. Worst of all, because it is quitequickly degraded by the sun, it will last only one or two summers as a greenhouse cover.

Polyethylene makes an excellent vapor barrier in insulated greenhouse walls. It may beformed into cold-water supply and drain piping for greenhouses also. The newpolypropylenes are resistant to higher temperatures and are now used in hot-water lines.

Styrenes or styrofoams are another thermoplastic which are used primarily forextruded foam boards as perimeter insulation for greenhouse foundations and wall panelsand for cushions for packaging fruits and vegetables. These plastics are essentially closed instructures and are thus relatively impermeable to water vapor flow and free from internalcondensation problems if the joints are sealed. They are often used in the construction ofstress skin wall panels but require reinforcing to control structural failure due to internalcreep. Styrenes will support fire and produce heavy smoke, but tend to be self-extinguishingwhen heat is removed.

Urethanes vary from thermoplastic to thermosetting, and from extremely hard, rigidmaterials to elastomers or "synthetic rubbers". Flexible foams, rigid foams, coating,adhesives, and solid mouldings are now available in a wide variety of greenhouse productsfrom insulation to coatings for metal and wood. Inert, foamed-in-place urethane has aK-value, heat loss, of 0.11 to 0,16 BTU/Hr/SF/° F,, which is about one half the loss ofconventional insulation materials which rely on entrapped air. As urethane insulation issubject to severe dimensional changes under extremes in temperature, its permeability towater vapor flow may be greatly reduced. These plastics emit heavy smoke and inflammablegases when burned or heated above 750° F. in confined spaces. Urethane spray-in-place kitsare now available in paint and hardware stores for insulation of foundation walls.

rHEATING

To determine the heating requirements of a greenhouse, many factors must beconsidered, such as the heat conductance of the greenhouse covering and other buildingmaterials, the size and shape of the structure, the growing season, indoor and outdoordesign temperatures, heating capacity of steam or hot-water baseboard radiation and unitheaters, efficiency of heating systems, heat emission of radiation at various temperatures,and climatological data for each area concerned, which are summarized in the appendix.Table A-G.

Also, a method of computing greenhouse heating requirements is illustrated in theappendix. Table H. A heating contractor, horticulturist, and/or agricultural engineer familiarwith greenhouse construction should be consulted for computing heating requirements, thedesign of the system, and selection of appropriate equipment.

The heating capacity of a boiler, furnace, registers, and radiation is rated in BTUoutput or input. A BTU (British Thermal Unit) is the amount of heat required to raise onepound of water one degree Fahrenheit. The heating system is usually designed on the basisof the lowest possible outdoor temperature during the particular growing period.

A combination of hot-water or steam baseboard radiation (fin tubes) and unit heatersis the ultimate in greenhouse heating. Oil- and gas-fired ventilation systems have recentlybeen developed for controlling the environment of greenhouses (Figure 10). Space heatersfired by wood, oil, and gas may be used with proper distribution of heat, particularly insmall structures. Perforated plastic ducts may be used for heat distribution as well as forautomatic ventilation control of greenhouses (Figure 11).

Figure 10 An Oil- or Gas-fired Ventilation System.

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Figure 11 Perforated Plastic Ducts for Air Distribution.

The hot-water boiler of a residence may be used, if of sufficient capacity, particularlynear the end of the household heating season. This is illustrated in the example shown in theappendix. Table H, A residential hot-air heating system is not too practical to tie into agreenhouse, as overheating of the house may occur unless hot-air ducts are zoned andseparate cold-air returns are provided.

Electric space heating is fairly inexpensive and easy to install but very costly tooperate. Soil heating cables, however, may be justified for propagation purposes such asgetting seedling plants started,

A battery-operated, low-temperature alarm which activates a bell in the residence towarn of low temperatures and/or failure of the heating system is desirable.

Types of Fuel: Fuel oil is well adapted to automatic control, is dependable and readilyavailable. Although it is more expensive than some other fuels, it is the most popular forhome greenhouse use.

O

Coal is the cheapest commercial source of heat in Alaska, regardless of the typefurnace. Compared to oil it requires more attention and work to supply the heating unitwith fuel and to remove ashes.

Wood may be the easiest fuel to obtain, expecially in outlying areas. Its use requireseither continuous attention or automatic draft controls to reduce temperature fluctuations.The cost of wood, if purchased, is somewhat similar to the cost of coal.

Natural gas is now available in some areas of the state at a cost comparable to oil. Thisfuel has all the advantages of oil and should be considered when a heating system is selected.

Heating values of fuels are shown in the appendix. Table C,

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SNOW LOADS

Snow loads are an important consideration in Alaska. In general, most greenhouses aredesigned for a snow load of 10 PSF (pounds per square foot), which may be entirelysatisfactory in areas where greenhouses are heated throughout most of the season. This, ofcourse, melts the snow and results in a minimum snow load. In Alaska, however, it isimpractical to heat the greenhouse in winter for the sole purpose of snow removal.

The framing system could be designed for heavier loads, but this increases the size ofthe members as well as the cost and limits the amount of available light for the plants. InAlaska the more logical approach in most situations is to provide temporary supports.Installing a row of movable columns down the center under each frame will increase thedesign snow load from 10 PSF to as much as 40 PSF. The supports may be hinged to eachframe and swung up against the roof during the growing season and dropped down to takecare of winter snow loads. Lumber or concrete footers or pads are recommended to preventsettlement of the post in the soil. Lightweight pipe columns must be reinforced againstbuckling, if used.

PLANT ENVIRONMENT

LIGHTING

The short period of daylight during the winter, and extremely low outsidetemperatures make it impractical to operate a home greenhouse in interior Alaska duringthese months. It is generally considered that the practical greenhouse season extends fromApril through October in interior Alaska. An earlier start can be made south of the AlaskaRange, The cost of supplemental light needed to grow plants in winter may exceed the costof heat in some cases.

VENTILATION

The lack of adequate ventilation to control excessive temperature and moisture is oftena cause of plant diseases. Although a manually operated wall and ridge ventilator may beused to control temperatures, constant vigil is required. A thermostatically controlled fan ismuch more reliable. The perforated plastic duct systems may be used for ventilation as wellas distribution of heat, particularly when tall crops such as tomatoes are being grown. Theperforated plastic duct ventilation system is illustrated in Figure 11. A complete change ofair every 1 to 1 1/2 minutes is generally considered adequate for warm-weather ventilation.An exhaust fan with multi -speed motor or adjustable pulley is desirable for reducing theventilation rate during cold weather. The fan should be monitored by a thermostat havingtemperature differential of not more than 1 ° F,

SOIL

Soil condition is usually less important than ventilation. Light or dry soils can bewatered, poor soils can be fertilized and heavy soils can be lightened. Selecting soil for thegreenhouse is, therefore, not too difficult. If the structure is located in a dry, warm spot, thesoil on which it is built is usually good enough.

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The average home greenhouse is small enough that the soil can be changed every two orthree years if necessary. A soil too light and dry can be improved by thoroughly mixingsome heavier soil or by adding peat moss or leaf mold. One part sharp sand and one part leafmold or peat mixed with two parts of heavy soil give a good mixture.

FERTILIZERS

Greenhouse soil can be used for many years, although serious trouble may developwith improper use of fertilizers.

Standard commercial fertilizers cause a build-up of salt in greenhouse soils over periodsof time. There are available a number of nearly 100% soluble fertilizers, which for allpractical purposes eliminate salt build-up. Too much fertilizer usually causes more difficultythan too little. Proper fertilization for one crop may be wrong for another. Tomatoes, forexample, thrive at a rate of fertilization that ruins a pepper crop. Some knowledge andexperience are required to handle greenhouse fertility problems.

Some knowledge can be gained by reading. Experience is more expensive but perhapsmore fun to obtain. Do some experimenting in a small section of the greenhouse. Tryvarious rates of fertilizers until you get good results. If trouble arises in a small part of thegreenhouse, the soil can easily be replaced.

Use concentrated fertilizers such as 8-32-16, 10-20-10-, or 10-20-20. The numbers referto the percentage of nitrogen, phosphorus, and potassium in the fertilizer available for plantuse, always in the order listed. Before planting, mix 1 1/2 pounds (or pints) of any of thesefertilizers into each 100 square feet of soil.

If the soil was heavily fertilized the previous year or if a lot of manure is used, applyone half of the above amount (3/4 pounds) per 100 square feet. Supplemental fertilizationis discussed later.

To help transplants get off to a good start, water them with a starter solution. Minor ortrace element deficiencies will cause poor growth at times. The amounts required are verysmall. Adding too much is as bad as not enough. Get in touch with your district agriculturalagent when a minor element deficiency is suspected.

Watch your plants carefully. If they show signs of poor growth and if their leaveschange to a lighter color, more fertilizer may be needed. The growth of the plants give thebest answer as to when and how much to fertilize. Study the plants and learn theirrequirements.

MANURE

Manure influences both soil conditions and plant nutrition. The quality of manuredepends largely on the kind, type of bedding and how the manure is stored before use.

Cow manure with straw bedding contains approximately six per cent nitrogen, one-halfof one per cent phosphoric acid, and five per cent potash (6-0.5-5). Some trace elements arealso present.

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Manure's greatest value is its humus. Some benefit is derived from the organisms itcarries. Manure should be well rotted. Mix one part into three parts of soil.

Fresh manure causes a temporary depression of nitrogen due to the increased demandfor this element by soil bacteria. Fresh manure may also introduce disease organisms andweed seeds.

In some places manure is difficult and costly to obtain. Nutrient levels are difficult tocontrol when supplied from manure. In the end, commercial fertilizer is generally moresatisfactory.

WATERING

Proper watering must not be neglected. Timely application of enough water is essentialfor good plant growth. Poorly timed or too light applications of water are detrimental. Theamount of water used and the timing of the watering should be such that the soil has all thewater it can hold without being soggy.

Watering is also a problem when benches are used. Large plants have to be watered atleast once a day. On bright sunny, days two or more waterings may be needed. Since lack ofwater is the apparent cause of blossom-end rot in tomatoes and is a major cause of poorgrowth in all plants, careful consideration should be given to this problem.

Greenhouse benches are often difficult to water properly. They tend to be too dry.The soil next to the sides of the bench dries out more rapidly than the center of the bench.This makes uneven amounts of water available for plant growth. Although the surface looksdamp, an inch or two down the soil may be powder dry. Dig down into the soil once in awhile and be sure that all of the soil is damp. Remember - as the plants grow, they use morewater and have to be watered more often.

Ground beds are easier to keep watered than benches. Small plants will not use asmuch water as large plants nor will they use as much when the weather is cloudy. In general,one good soaking a week will be enough. Fill the furrows to the brim when watering. Lessfrequent but more thorough waterings are better than frequent light wettings.

TRANSPLANTS

RAISING SEEDLINGS

Germinating seeds are often damaged by fertilizer. No fertilizer should be added to thesoil or other media (when a small container is being used) in which seed is sown. Until thefirst true leaves of the young plant are formed, the seed itself furnishes all food for thegrowing seedling.

The growing media needs to furnish only moisture and support for the plants. It mustallow easy removal from the starting flat. Sharp, clean sand is a convenient material usuallyavailable. It will hold water but not become waterlogged. It is easily sterilized to prevent"damping-off" by baking in an oven until the soil temperature reaches 180° F. (About onehour.) Vermiculite, an expanded mica product is also good, and it can be bought in manyseed stores. It does not need to be sterilized when it is new. Milled sphagnum moss issatisfactory. Soil may be used, but plants cannot easily be removed from soil withoutinjurying their roots. Soil should always be sterilized.

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The container for starting seed should be shallow and have drainage holes in itsbottom. An eight-inch square cake tin,two inches deep, is about right. More plants can bestarted in a container of this size than can be used in the home greenhouse or garden.

TRANSPLANTING

Seedlings should be transplanted when their first true leaves appear. It is best totransplant young plants and give them room to grow.

Transplants need a good, light soil containing plenty of organic material, A goodpotting soil can be made by combining two parts of soil, one part of sand, and one part leafmold or peat.

When large quantities of sterile soil are needed, other methods are better. Wateringnewly transplanted seedlings with a solution of a soil fungicide will help control"damping-off". Follow directions printed on the containers carefully. Too heavy anapplication may injure the plants.

Seedlings are transplanted into many types of containers. Flat wooden boxes threeinches deep, six inches wide,and ten inches long are handy. They are small enough to becarried easily and accommodate at least 15 plants. Plants are set into the flats at two-inchintervals. Outside rows are an inch from the sides of the flat. The bottom of the flat shouldhave one-eighth-inch gap between boards for drainage.

Pots, tin cans, and other containers can be used successfully if they are well drained. Acontainer three inches in diameter is big enough for a single plant.

To remove plants from flats, slice through the gap between plant rows with a knife.Use a spatula or trowel to lift the plant from beneath.

Plants are easily removed from pots by placing fingers of one hand across the top onboth sides of the plant stem. Invert the pot and bring its rim down sharply upon the edge ofany solid object. The plant and soil will slide down into the hand without disturbing theplant roots.

It is more difficult to remove plants from tin cans and other straight sided containers.This usually can be done by running a knife blade around the inside of the can. To be surethat the soil around the plants is in good condition to be removed, water it well a few hoursbefore transplanting.

Carefully prepare the beds into which plants are to be transplanted. Work in thefertilizer as the soil is spaded or worked. Break up all clods and smooth the surface with arake. Space the rows carefully using a string to keep them straight. A stick cut to the desireddistance between plants is useful in spacing them properly in the row.

Do not dig the holes until ready to set a plant. Make these holes large enough to receivethe ball of soil around the plant roots and deep enough so that about half an inch of newsoil will have to be placed over the plant ball to fill the hole.

After placing the plant in position, pour a cup of starter solution or water around theroots. Then rake soil into the hole and press it firmly into place. For more details on seedingand transplanting, get a copy of Extension Publication 135, "Gardens in Alaska" and/orP-32, "Transplanting and Seed Starting".

-18-

PLANT PROBLEMS

INSECT PESTS

There are seldom serious insect problems in greenhouses that remain unheated duringthe winter. Aphids will occasionally infest a greenhouse during the season. Spider mites orwhite flies are often brought in on purchased plants or those over-wintered in the home.These insects cause trouble when uncontrolled. Insecticides are available for general useagainst these insects. Follow the directions on the label. See Extension Publication137,"Vegetable Garden Insects".

White flies: These are tiny, soft bodied, fly-like insects with white, waxy wings. Whenthe plant foliage is disturbed, the insects flit about and look like small, self-powered snowflakes. White flies injure the plants by sucking sap from the leaves. They are brought intothe greenhouse on infested plants.

Spider mites or red spider: Spider mites are not true insects. Adults have eight legs,while immature forms have only six. They may be red, yellow, or green in color. The eggsare tiny, colorless globules. The cyclamen mite is so small that it is almost invisible to theeye.

Plants purchased from infested sources and brought into the greenhouse cause most ofthe trouble. It is always best to treat purchased plants with an insecticide before takingthem into your greenhouse.

MAJOR DISEASES

Conditions within the greenhouse make it a perfect place for plant disease to spread,"Damping-off", leaf mold and powdery mildew are major diseases. At times others will befound. All of these diseases can be controlled with ordinary care and the timely applicationof proper control measures.

The appearance of a disease in the greenhouse should signal prompt control action.Few diseases become serious when control measures are taken. Watch all plants. Investigatecarefully when any plant appears to be abnormal. Call in the district Extension agent. He isqualified to answer your questions. Do not wait and see or control may be impossible.

"Damping-off', Figure 12, is one of the main causes of death in young seedlings. Thisdisease is caused by several types of soil organisms present in new as well as in old soils.Cold, damp weather favors this disease. Seed treatment and soil sterilization may help tocontrol it. The organisms that cause "damping-off" attack seedlings weakened by poor light,low temperature, overly moist conditions, and poor air circulation.

-19-

o

Figure 12.— Damping-off in tomato seedling. This disease canattack all plant seedlings and is found in any soilwhich has not been sterilized. Sterilization and seedtreatment help control the disease.

Leaf Mold: (Figure 13). This disease attacks tomatoes. Its first noticeable symptom isthe appearance of irregular, yellow spots less than a half-inch in diameter on the uppersurface of the leaves. On the underside of these leaves, directly under these yellowed areas,will be a brown, felt-like splotch of fungus spores. A severe infestation may cause the foliageto dry up completely and plants eventually to die.

/-"-.

Yellow spots 1 /2 inch in diameter

Figure 13.— Leaf mold attacks tomatoes. Yellow spots develop onthe upper surface of the leaf with brown, felt-likesplotches developing directly below these on theundersides of the leaf. To control this disease keepthe humidity down and the temperature above 60° F,

-20-

Spores of the fungi which cause leaf mold are brought into the greenhouse on seeds.After the initial infection, spores survive in the soil. Once the disease is present, it spreadsfrom one leaf to another or from one plant to another, for the spores are dry and welladapted for movement by air. The spores require a very high humidity for germination andinfection. The disease becomes serious in Alaskan greenhouses in late summer whentemperatures start to drop and many cloudy, cold days occur. At this time, tomato plantsare large. They transpire large quantities of water. In poorly ventilated structures, humidityis high. Moisture condenses on the greenhouse glass and frequently keeps the plant leaveswet.

To control this disease, keep the humidity down by ventilating. On cloudy, cold daysprovide enough heat to keep the greenhouse temperature from dropping below 60° F. andopen vents to keep the humidity from building up.

Powdery Mildew: Figure 14, This is not a widespread disease in Alaskan greenhouses.It is present in some areas and may cause heavy damage to cucumbers. The first symptom isusually the development of white spots on the older leaves. These spots have a powderyflour-like appearance which accounts for the name. The fungus grows on the surface of theleaf and feeds on the plant. Spores are produced in abundance and do not require highhumidity for germination. This disease is thought to grow only on living plants.

Powdery flour-like appearance

Figure 14,— Powdery mildew is not common, but does attackgreenhouse plants occasionally. It can be controlledwith fungicides.

Powdery mildew can be controlled by fungicides. Although sulfur controls powderymildew, cucumbers are sensitive to sulfur and care must be taken to apply it lightly. Dustingsuifur is available from seed supply stores. Use a duster to apply the sulfur if one is available.The sulfur can be placed in a cloth bag and shaken gently over the plants.

-21-

GREENHOUSE CROPS

Many crops can be grown in Alaskan greenhouses. Tomatoes, cucumbers, beans, andlettuce are most common. The growing methods described below can be adapted tointercropping.

ov

TOMATOES

Tomatoes are the most widely grown greenhouse crop in Alaska. They are easy to growand usually produce some fruit even under poor growing conditions.

Tests conducted by the Alaska Agricultural Experiment Station show that the large,vigorous hybrid varieties produce the highest yields of good-quality tomatoes. Get a copy ofVegetable Varieties from your Extension Service Office for the latest recommendedvarieties. For best results, tomatoes should be planted in ground beds where they have anopportunity to grow tall and are not hampered by restricted roots as they are in thebenches. In greenhouses where benches are used, small varieties are better. The varietychosen has a great deal to do with the success of the crop. Try a few plants of a new varietyeach year until you find one well suited to your conditions.

Tomatoes should be seeded 8 to 1 0 weeks before the greenhouse is ready. Most peoplestart them in their homes, transplanting them into flats or other containers placed inwindows having southern exposures. This method produces tomato plants that are usuallyfree of disease and insects.

Start heating the greenhouse three or four weeks after the seeds are sown. This givesthe greenhouse soil a chance to thaw out and warm up enough to be ready for the plants,More time may be needed in some parts of Alaska.

C '

The soil should be fertilized and turned as soon as it can be worked. If the crop is to begrown in ground beds, furrows and ridges should be made. Furrows should be formed atright angles to a center aisle or path, Ridges should be three feet apart with the first ridge 1 8inches from the end wall. The ridges should be six inches high. (Figure 15).

between plants

Figure 15.- Ground beds are utilized best as furrows and ridges ingreenhouses.

-22-

To form the ridges^ use a round pointed shovel. Dig a trench the width of the shovelfrom the center aisle to the outside wall Throw half the soil removed from the trench toeach side so that ridges are built. Smooth the sides and tops of the ridges until a good flattransplanting bed is ready. The bottom of the furrow should be smooth and have a slightslope away from the aisle. A good watering two days before transplanting will bring the soilinto good condition. Leave an 18-inch space between plants in the row.

Tie twine to overheadwire (tie lower end tostake)

Flower cluster

Pinch off lateralswhere they join thestems

Twine or "twistem" tosupport plant on twine

Figure 16. How to Support and Prune Tomatoes

Tomatoes should be pruned to a single stem by removing all shoots (where the leavesjoin the stem) as in Figure 16, Tomato plants should be supported by a double strand ofbinder twine or strong rough cord suspended from a wire stretched tightly across thegreenhouse about seven feet above the row and directly over it. Tie the suspended twine to astake driven into the soil at the base of the plant. This keeps the plant from swaying out ofline. As it grows taller, tie it to the supporting twine with a short piece of twine or a"Twistem". Tie tightly to the support and loosely about the plant. "Head back" the plantby removing its terminal bud when it grows above the overhead wire,

Leaf pruning is unnecessary and should be avoided. Tests show that fruit yields arereduced when leaf pruning is practiced. Dead or damaged leaves can be removed.

-23-

As the tomato plant grows, it will need food. Use the same fertilizer that was broadcaston the bed. When the first blooms appear, side-dress each 100 square feet of bed or bench /~Nwith 1/2 pound (or pint) of complete fertilizer. Work it lightly into the soil. Side-dress \...)about every two weeks after the plants start to bloom. The best time to apply fertilizer isshortly before watering the plants. Then the fertilizer will dissolve and be carried downaround the plant roots.

Too much fertilizer can be applied. This is especially true when the soil has beenfertilized in this way for more than one year. The first symptom of overfertilization is acurling under and back of tomato leaves. This occurs first on the new leaves at the top ofthe plants. The distortion of new leaves is called "nitrogen curl". When it appears, it is bestto withhold further fertilization. From then on,fertilization has to be balanced against theappearance of the curl.

Although tomato blossoms are self-pollinated, some help may be required to getenough pollen on the pistil to cause full fruit development. This can be done by gentlyrapping the plants with the hand or by using a battery-operated vibrator. An electrictoothbrush works nicely.

Under Alaskan conditions, fruit-setting hormone sprays are usually unsatisfactory.Hormones cause deformed fruit and are actually injurious if applied to the growing point ofthe plants.

TOMATO TROUBLES

Blossom-end rot, caused largely by an uneven moisture supply, is responsible for thegreatest loss of tomatoes in the home greenhouse. A uniform supply of water and uniformtemperature will hold this trouble to a minimum. ^N

Gray mold is a common fungus disease that causes difficulty when humidity is veryhigh. It can be largely controlled with good ventilation and enough heat, especially at night,so that no condensation will occur within the house.

Leaf mold, Figure 13^ is also a fungus. It can be identified by yellow spots on theupper surface of the leaves. On the back of the leaf, will be a brown felt-like cushion. Whentemperatures drop and humidity goes up, conditions are right for leaf mold to appear. Goodventilation and added heat will control this disease.

Mosaic or tobacco mosaic is a virus disease that occurs regularly in Alaska. It is carriedon tobacco (also on smokers hands) and is easily passed on to tomato plants. The bestcontrol is to keep smokers away from your plants and greenhouse. If you smoke, wearrubber gloves when working with tomatoes,

"Damping-off", Figure 12, can be controlled by treating the seed with a fungicidebefore planting, thinning to allow good air circulation around the stem of each plant,keeping the soil surface slightly dry where it comes in contact with the seedling stem, andsprinkling the seedling with a solution of fungicide. Follow directions on the package.

Often, near the end of the greenhouse season, many green tomatoes are left on thevines after it is impractical to keep heating the house. Many of these can be saved, althoughthey are a p p a r e n t l y completely green, by wrapping each one in an old piece ofnewspaper, packing them lightly in a box, and storing them in a cool area. They will ripen,afew at a time,for another month. (

-24-

Another method of ripening is to pull the vines and hang them upside down in thebasement or garage, where the fruits will ripen for about another month. If there are only afew tomatoes left, simply set them along a warm, bright windowsill. This will save them fora week or more.

CUCUMBERS

Cucumbers are the second most important crop in Alaska greenhouses. Most of themethods for raising tomatoes are also used for cucumbers. Fertilization, watering, spacing,and preparation of the seedbed are the same. Seeding, pruning and pollinating are handleddifferently.

Although cucumbers may be started like tomatoes and later transplanted, it is usuallybetter to plant the seed in hills where the plants are to grow. There are difficulties associatedwith both methods. Transplanting cucumbers, melons, squash, or any of the vine crops, isdifficult because the roots will not stand much disturbance. Seeding in plant bands or flowerpots from which they can be removed without disturbing the roots is satisfactory. Peat potsor peat pellets cause the least setback. If the seed is started on ridges in the greenhouse, theridge tops must be kept moist and extra seed used. Then when the plants are well started,they must be thinned until only one plant remains in a hill.

Tie twine to overheadwire

Break off laterals pastsecond node

FemaleFlower (pickle)

MaleFlower (enlarged)

Tie lower end of twineto stake

Figure 17.— How to support and prune cucumbers. Laterals maybe pinched off past second node if last bloom is maleor fails to set fruit.

-25-

Cucumbers put out side shoots like tomatoes. These are not removed close to the stem,as they are in pruning the tomato plant. Let them grow until the second blossom bud f~\, (Figure 17), Then cut the shoot off beyond this point. Cucumber vines are trained -—'

up on twine, like tomato plants. Prune the plant back when it grows above the supportingwire,

The cucumber blossom does not contain both the male and female flower parts. Theseare found in separate blooms. The male flower contains the anthers. Female flowers containthe pistil, on which pollen must be placed if the fruit is to develop. Female flowers areidentified by a small cucumber (ovary) behind the flower. Figure 17. .

The home greenhouse operator is often concerned because only male blossoms seem toform, although the plants look healthy, Male flowers form first, when the length of daylightis increasing. Female flowers start forming as daylight decreases. Both types of blooms areusually developing by mid-June. Length of day, variety, nutrition, and temperature, all playan important part in flower production. Some varieties bear more female flowers thanothers. By increasing the nutritive level, more female flowers are encouraged to form.Likewise, as the temperature is increased, more female blooms develop. Under nearly allconditions, several male flowers form for each female flower.

Once both male and female blooms are found at the same time the problem ofpollination must be met. Insect pollination of cucumber flowers will not ordinarily occur inthe greenhouse. So, female flowers must be pollinated by hand. The best way to do this is topick a male blossom and remove its petals. Grasp the stem of the flower between the thumband forefinger. Place the anthers gently in contact with the pistil of the female flower andspin the male flower with the fingers. The use of an artist's paint brush or a feather totransfer the pollen also works well. Pollination of new blossoms should be done at least _^every third day to avoid missing any newly opened blooms. On warm summer days when T )the greenhouse door and ventilators are wide open, some natural pollination from wild beesmay take place. Spraying with hormone sprays is not satisfactory for cucumber production.

Diseases in greenhouse cucumber production are usually limited to "damping-offwhich can occur in most all seedling plantings in Alaska, powdery mildew which is a fungusdisease that shows up as white spots on the leaves (Figure 14), and gray mold rot whichattacks plants only under conditions of very high humidity. For control of "damping-offsee Tomato Troubles on page 24. Powdery mildew can be controlled by a light dusting with"flowers of sulfur" but cucumbers are damaged by large amounts of sulfur. Gray mold rotcan usually be controlled by good ventilation.

Harvest cucumbers as soon as they are ready. The number of new female flowers willbe reduced if mature fruit is left on the vine.

SNAP BEANS

Two types of beans are grown in greenhouses. These are bush and pole beans. Eitherkind will grow well and produce a good crop, Pole beans usually yield more than bushvarieties. Two rows of beans are planted along the top of each ridge parallel to each otherand about four inches apart. Seeds are placed about an inch apart in the rows, and about aninch below the surface. Keep the ridges damp until the sprouts have emerged. Thin until thebest plants are left, about four to six inches apart in the row,

Pole beans are supported with twine like the other tall growing greenhouse crops.

-26-

String a wire tightly along the top of the ridge midway between the two rows of beansand about three inches above the soil. This wire is fastened securely to stakes driven into thesoil about every two feet along the row. String another wire six feet above the ground.Lengths of twine are tied to the top and bottom wires about eight inches apart, or acontinuous length is passed over and under the two wires, with each turn of the twine abouteight inches apart on both wires. Plants fasten themselves to the twine. Stray growth willrequire some training. Head back the bean plants as they grow above the top wire.

Pole beans may also be planted in hills eighteen inches apart and trained likecucumbers. Four or five seeds are planted per hill and later thinned to three plants.Pollination is not a problem with beans. The bean is self-pollinated. Pollination occursbefore the flower is in full bloom.

Other cultural practices are similar to that given for tomatoes and cucumbers. Warm,well-drained (preferably sandy) soil is best for beans. The fertilization level is not as criticalfor beans as it is for the other two crops. The uniform application of water becomesincreasingly important the higher the mounds or ridges are built and as drainage becomesmore rapid.

PEPPERS

Peppers are a common and productive greenhouse crop. They do best in well-drained,moist, light, warm soil which should be well supplied with humus. They should not be asheavily fertilized as tomatoes or cucumbers. That is why they never seem to do as well whenconditions are best for tomatoes. Because the early culture of both vegetables is the same,usually they are set out with the tomatoes. It is a better practice to set alJ of the pepperplants in a group at one end of a bench or bed to avoid over-fertilization. Like the tomato,they have perfect flowers and need no special attention to become pollinated. Since peppersare naturally determinate, they are fine for bench culture. Peppers are rather free of diseasesas long as there is good ventilation and air circulation around the plant. Harvested pepperscan be kept for several weeks if stored in a cool area with considerable humidity.

This is a much-neglected plant that can be easily grown in the home greenhouse inAlaska. It is naturally slow growing and, therefore, must be given an early start in order toform during the greenhouse season. The one condition that must be guarded against is lowtemperature. The plant growth is always checked and often permanently stunted iftemperatures fall below 50° F.

This is a tender plant that does not stand transplanting well. The set back is not asgreat if seeding is done directly into peat pots or peat pellets and then thinned to a singleplant in each pot as early as possible. Great care should be taken not to disturb the rootswhen transplanting and to keep the soil moisture high. Otherwise the large leaves willevaporate moisture so rapidly that permanent wilting may occur.

The soil should be warm, light, well drained, and rich. Under these conditions, fromtwo to five large, dark purple (or nearly black) fruits should develop.

The mature fruit can be picked and kept for several weeks in a cool, moist area wherethere is good circulation of air around each fruit.

-27-

LETTUCE

Leaf lettuce is easily grown in greenhouses, although the principle reason for this is to v,Jsecure an early crop. It prefers both cool soil and cool air temperatures and, therefore, doesnot always fit into the greenhouse program when other plants are being grown. If conditionsare too warm, the lettuce will be bitter and go to seed quickly.

A well-drained soil in good tilth and with an abundant supply of moisture is best forrapid lettuce growth. Only forty days are required to grow salad lettuce; and for this reason,it is often used as an intercrop with a slower-growing main crop.

One serious trouble is that bottom rot develops on the lower leaves. This can be greatlyreduced by planting on narrow ridges and allowing a good circulation of air around eachlettuce plant. Tip burn is also a troublesome condition in lettuce, but its cause and controlare poorly understood. It occurs less frequently when cool temperatures are maintained andunder optimum growth conditions.

Head lettuce usually fails to head properly under greenhouse conditions, so only leaflettuce is recommended.

Lettuce does not store well. So, the best practice is a series of small plantings that canbe used fresh.

RADISHES

oThese are normally a garden crop, but a few feet of row are often planted between \other crops in the greenhouse. Their culture is too well known to repeat. Conditions suitablefor lettuce will be fine for radishes.

ONIONS

Although onions are seldom considered a greenhouse crop, they respond well.

Soil conditions are very important in onion culture. It should be loose, well drained,warm soil, but it should be highly retentive of moisture and well supplied with humus.Onions are very shallow rooted. Both moisture and fertilizer quickly drop below the rootzone unless replaced at the soil surface often. For this reason a small amount of fertilizerused at the proper time is much more effective than a larger amount mixed through all ofthe soil.

Onions may be started from seeds or sets, but seed onions do not usually reach a sizesuitable for dry storage the same year.

Onions should be stored in a dry place where the temperature is well above freezing.

-28-

SWEET CORN

Planting a few kernels of sweet corn in the home greenhouse is a popular, thoughseldom worthwhile, practice. Corn needs a high temperature, both day and night, to do well.Most of the other popular greenhouse plants like to have the night temperature at least tendegrees cooler than the day. Also, pollination is always a problem in the greenhouse. Windcurrents normally play a major role in getting pollen from the top of the corn down ontothe silk. This does not take place in a greenhouse. Corn should be set in blocks of severalrows wide, which is seldom done inside. Its size requires that a large amount of space beused when only a small return can be expected.

From these facts one must conclude that, although sweet corn can certainly be grownin a home greenhouse, it is not an efficient use of space and is not a recommended practice.

These three plants, in general, require greenhouse conditions to grow well in Alaska.Although a few are grown each season, it cannot be considered efficient use of limitedgreenhouse space. The plants and leaves grow so large that only one or two will causeexcessive shading of other crops in a small greenhouse. In addition to this, the individualfruits must be supported by special net cups, otherwise their mature weight will pull downvines and break stems.

For those who still desire to try their hand at growing them, follow the culturalmethods outlined elsewhere for cucumbers.

-29-

APPENDIX

Table A Heat Transmission Coefficients (C) of Common Building Materials

Table B Efficiency of Heating Systems

Table C Heating Value of Fuels

Table D Heat Emission of Radiation

Table E Fin-Tube Radiation Capacity Rating

Table F Capacities of Typical Projection-Type Unit Heaters

Table G An Example of Computing Greenhouse Heating Requirements

Table H A Method of Computing Greenhouse Heating Requirements

Table I List of Greenhouse Plans

Table J List of Greenhouse Publications

C

(For help in working with these charts, consult your district agent, Cooperative Extension Service)

-30-

TABLE A HEAT TRANSMISSION COEFFICIENTS (C)OF COMMON BUILDING MATERIALS

BTU/Hr - S.F, - ° F. *

BTU/Hr-S,F. -°FMr Space:

Vertical, 3/4" wideSame, with reflective

lining

Concrete Blocks, 8x8x16:Sand & gravelLight weightSame, cores filled with

expanded mica[nsulation -- per inch:

Blanket or battLoose fill:

Expanded MicaGlass or mineral woolSawdust & shavingsStraw

Rigid type:FiberboardPolystyreneUre thaneGlass, cellular

1.10

0.46

0.900,50

0.25

0.27

0.320.270.410,70

0.330.250.170,44

BTU/Hr-S.F, -°FRoofing:

Asphalt, built up3/8"

Aluminum .019"Steel 26 G.A.

Surface Film:Interior (horizontal)Exterior (15 mph wind)

Wallboard:Asb. cem. board 1/4"Fiberboard, 1/2"Plywood, 1/2"Wood Board, 3/4"Plasterboard, 3/8"

Floor:Concrete, on grade

1.3326,90 +5.63

1.656,00

1.501.502.121.023.73

0.10

* Airfilm and airspace coefficientscoefficients to obtain total heat

must be added to building materialtransmission values (U).

TABLE B EFFICIENCY OF HEATING SYSTEMS

Type Fuel

Anthracite CoalAnthracite CoalBituminous CoalBituminous CoalOilOilGasElectricityWood

Method of Firing

Hand-fired with controlsStoker-firedHand-fired with controlsStoker-firedDesigned unitConversion unitAll typesResistance heatersHand-fired with controls

Efficiency

60-70%60-80%50-65%50-60%65-80%60-80%70-80%

100%50-60%

-31-

TABLE C HEATING VALUE OF FUELS

O

BTU/lb

Propane 21,550Natural 23,890Coal 13,000Fuel Oil 19,800Gasoline 20,383Wood, Birch 4,300ElectricityWood, Spruce 4,700

(1) 1 cord = 128 cu, ft.

BTU/unit volume

91,000/gal.l,000/cu,ft.

26,000,000/ton138,000/gal,122,300/gal,

16,000,000/cord (1)3413 KWH

12,600,000/cord (1)

TABLE D HEAT EMISSION OF RADIATION

O

MeanTemperaturedegrees F

170180190200215230240

BTU Output/Sq. Ft. Radiation

148167188209240273293

-32-

TABLE E FIN-TUBE RADIATION CAPACITY RATING

Tube Fin

1" 2"x4-l/4"

1" 2"x4-l/4"

1" 3"x3-3/4"

1" 3"x3-3/4"

1" 3"x3-3/4"

1" 3"x3-3/4"

1-1/4" 4-1/4x4-1/4"

1-1/4" 4-1/4x4-1/4"

1-1/4" 4-1/4x4-1/4"

3/4" 2-3/8x2-3/8"

1/2" 2-3/8x2-3/8"

3/4" 2-3/8x2-3/8"

Hot Water Ratinq

RowsHigh

1

1

1

2-7 1/2" cc

2-10" cc

2-15" cc

1

1

2-7 1/2" cc

1

1

2

Fins/Foot

40

32

38

38

38

38

38

40

38

56

56

56

180

580

456

745

1267

1693

1714

1201

1200

2040

710

710

710

Temperature200

BTU/Hr. /

710

610

929

1579

2110

2136

1496

1496

2543

870

870

950

°F220

Lin. Ft.

810

690

1125

1914

2560

2583

1818

1800

3100

1030

1030

1130

SteamRatinq•i i . - . I «<

215

780

670

1080

1836

2453

2484

1740

1740

2957

—

—

-33-

TABLE F CAPACITIES OF TYPICAL PROJECTION-TYPE UNIT HEATERS

Air Flow

MotorH.P. RPM

1/30

1/8

1/3

1/2

1/3

1/2

1

1

1

17

21

1500

1725

1725

1725

1140

1140

1140

1140

1140

HeatBTU/Hr

55,300

97 ,000

141,500

194,000

233,000

327,000

435,000

451,000

560,000

I/Output

EDR

230

405

590

807

970

1365

1815

1880

2330

Final , @ FinalTemp,^7 Temp,°F

°F GFM 31

132

123

118

111

126

120

123

122

128

710

1420

2250

3770

3250

5010

6360

6700

7580

FanSizeDia,Inch

10

12

15

18

20

22

25

27-1/2

30

2 pounds steam at 60° F, entering air

Water Temperature Drop (°F.) Heat Output (BTU/Hr)500 x Gallons per min.

31 Final Air Temperature (°F, = BTU/Hr + Ent, Air Temperature

c

LOSSxCFM

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TABLE G AN EXAMPLE OF COMPUTING GREENHOUSE HEATING REQUIREMENTS

April May June July Aug. Sept. Oct. Total,

Anchorage

Bethel

Big Delta

Cordova

Fairbanks

Fort Yukon

Homer

Gulkana

Juneau

Kenai

Ketchikan

Kodiak

Matanuska

Nome

Northway

Seward

Sitka

Valdez

Wrangell

Minimum (°F.)Mean (°F.)Degree Days

-2135,7879-2125.91173-1429.21074936.2864-3229.41068-2421.51305-933.7939A29.41068741.0720-2222.012903143.66421736.6852-1637.1837-2121.21314-4226.01170_j37.98132541.1717434.99032947.2534

145.95922439.08062347.15552043.7660047.1555743.6663641.67252044.36422648.35181232.89983450,14623442.9685847.25522035.0930444.86261444.76292747.15551343.16793349.7474

3154.53152851.64023657.12372950.24423058.41983058.81862949.24743154.43183154.83062843.36514055.22943949.64772755.42882945.95733055.82763151.73993752.33812850.44383954.9303

3557.12453154.73193959.61673453.23663459.71643461.31153452.63843657.02483656.92512749.74744558.22114253.83473157,72263249.54813458,42053655.52944155.82853352.93754357.3239

3155.62913352.33943454.83163052.43912354.33322855.13073352,53882853.03722756.22732553.63564258.91893855.23042755.42983549.04962253.23663355.42973556.62602951.64153656.5264

1947.85162544.66121943.66422247.65221243.66421141.27142246.55552243.46482751.34111153.2

L3543754.63123349.7L4591647.7

L_5192041.96931141.67022649.44683052.83661446.05703051.7399

-635.0930431.41042-1825.612211139.8781-2826.21203-820.813701036.8874-1927.311681643.9654-546.35803047.65392441.5729A35.6911329.71094-1721.71342940.47632645.5604537.28622644.9623

3768

4748

4212

4026

4162

4660

4339

4464

3133

4703

2649

3853

3631

5581

4687

3663

3168

4242

2836

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TABLE H AN EXAMPLE OF COMPUTING GREENHOUSE HEATING REQUIREMENTS

1, Dimensions of Greenhouse

DoublePlastic

Connectedto house

W(width) = -JO f t . . L (length) = 10ft. , E (eave height) = 5ftR (ridge height) = 10ft , S (slope roof) = 7,1ft ,

Volume = 75,0 sq. ft. (End area) x 10. ft. (length) = 750 cu. ft.

2, Design Temperatures

Ti= 60° F. To = -20° F.(Inside) (Outside)

Tg= 17.0(Ground)

3, Structural Heat Loss

Floor

Roof

Side

End

ExposedArea(S, F.)

100,

142,

100,

75,

U-valueBTU/Hr/°F)

0.10

0,90

0.90

0,90

Temp.Diff.°F,

43

80,

80,

80,

Structural Heat Loss

(BTU/Hr/°F) (BTU/Hr)

10. 430.

128,

Total 417, 0,698 avg. 80,

90,

68,

291, avg.

10,240

7,200

5,440

23,310

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4. Infiltration Heat Loss

Hi (infiltration heat loss) = [ 1,5 Changes/Hr x 750, Cu. Ft. ][1.1 BTU/Hr/Deg./CFM x 60.]

- 17, BTU/Hr/Deg.

5. Ventilation Heat Loss

Ventilation fan size 1125. CFM (1 1/2 x VOLUME)Hv (ventilation heat loss) = 1125 CFM x 1.1 BTU/Hr-Deg.-CFM

= 1236 BTU/Hr/Deg,

Fan size is based on summer ventilation and should not be operated at full capacity duringheating period. Set fan thermostat to operate at 4 - 5° F. higher than furnace thermostat.

6. Heating Requirements

Ht (total heat loss) = Hs + Hi = 291 + 17 = 308 BTU/Hr/Deg.H (heating requirements) = Ht x Td = 24,640 BTU/Hr

7. Size Heating System

Type fuel: Coal, electricity, gas, (oil) or wood (circle one)Methods of firing: fAutomatic]) or hand firing (circle one}Type heating system: Space heater, hot air furnace,(Ept water boiler^ or steam

(circle one)

Structural Heat Loss = 24,640 BTU/HrEfficiency Loss = 30,% x 24,640 BTU/Hr = 7390 BTU/Hr

100Pickup Loss = 20 % x 24,640 BTU/Hr = 4930 BTU/Hr

100Piping Loss = % x BTU/Hr = BTU/Hr

Boiler Capacity = 24,640 + 7390 + 4930 + =(structural) (efficiency) (pickup) (piping)

36,960 BTU/Hr.

8. Fuel Consumption

Location: Homer, AlaskaHeating period: April 1 to June 30Degree Days: 2053 @ 65° F. baseType fuel: oil and Heat output 138,000 BTU/ gal.

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9. Use of Household Heating System For Heating Greenhouse

Size of heating plant (gross or^ne^: 66,000 BTU/HrHeat loss of house: 360 BTU/Hr/Deg. (1-Story 1150S.F.)Design temperatures: house 70° F.. . greenhouse 60° F.Heating period of greenhouse: April 1 to June 30Heat available for heating greenhouse:

Outside Temperature DifferentialTemp. House Greenhouse(Deg.) (Deg.) (Deg.)

Heating Requirement (BTU/Hr.)Net House Balance GreenhouseAvail. Reg'd Avail. Reg'd

50403020100

-10-20

2030405060708090

1020304050607080

66,00066,00066,00066,00066,00066,00066,00066,000

7,20010,80014,40018,00021,60025,20028,80032,400

58,80055,20051,60048,00044,00040,80037,20033,600

3,0806,1609,240

12,32015,40018,48021,56024,640

In this particular example the household heating plant is of sufficient size to heat theresidence to 70° F. and the greenhouse to 60° F. at an outdoor temperature of-20° F. Theminimum recorded temperature for Homer during the period (April 1 — June 30) was -9° F.Table G, However, one must be extremely cautious about operating the exhaust fans, as theventilation heat loss (1236 BTU/Hr/Deg) would be nearly 75 times as great as the totalstructural and infiltration loss of the greenhouse (17 BTU/Hr/Deg), paragraphs 4 and 5.

10 RadiationType radiation:

Size radiation:

Fin tube or unit heater (circle one)

1" tube, 3" x 3 3/4", 2-7 1/2 cc, 38fins,1267BTU/Lin, Ft Table E

Boiler water temperature: 180° F,

Length = 24.640 BTU/Hr = 19.5 Lin. ft.1267BTU/Hr/Lin. ft

There is sufficient side wall length on the two sides of the greenhouse to install thecalculated length of fin tube radiation in this particular example. Also a projection-type unitheater could be selected as shown in Table F, Appendix. The 1/30 H,P. unit heater wouldhave a heat output of about 38,5000 BTU/Hr based upon 180° F. water, based on Table D.

O

NOTE: Copies of the form used to estimate heating requirements may beobtained from the Cooperative Extension Service, University ofAlaska, College, Alaska 99701

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TABLE I LIST OF GREENHOUSE PLANS

The following greenhouse plans may be ordered from this office, There is a minimumcharge of $2.00 for 1 to 3 sheets and 50 cents for each additional sheet.

4926 Portable Plastic Greenhouse, 1 sheet. 8'-6" width X 12'-0" length X 7'-0" height,1" X 8" treated wood base, curved laminated arches @ 3'-0", for either plastic film or rigidplastic covering.

5189 Sash Greenhouse, 1 sheet, 10'-4" width X 18'-8" length X 3'-0" eave, 6'-0" ridge,concrete masonry wall, wood sash bars, hinged roof, raised benches, for either glass or rigidplastic cover.

5941 Plastic Covered Greenhouse-Coldframe, 2 sheets, 5'-0" width X 7'-8" length X 5'-7"and 7'-7" side walls, roof may be removed and used as coldframe, 2" X 2" wood structural members,for either plastic film or rigid plastic.

5971 Hotbed and Propagating Frame, 1 sheet. 6'-0" width X 6'-0" length X r-8" eave X3'-4" ridge, 1" X 8" treated lumber base, rigid arch frames of 1/2" thin-wall electrical conduit,for either plastic film or rigid plastic.

5980 Plant Growth Chamber Roomette, 2 sheets. 2" X 2" wood frame treated plywood shell,48" width X 96" length, 48" height, combination fluorescent and incandescent growth lamps,100 CFM blower.

6029 Greenhouse Framing, 2 sheets. 22'-10" width X 48'-0" to 96'-Q" length, 6'-3" eave,12'-Q" ridge, treated timber or pole foundation, 2" X 6" rigid frames @ 4'-0" o,c, with plywoodeave gussets, for either plastic film or rigid plastic.

6080 Mini-Hotbed and Propagating Frame, 1 sheet. 3'~6" width X 5'-0" length X I'-IO"ridge, 2" X 8" treated wood base, 6 X 6 No. 8 welded wire roof support, soil heating cable,for plastic film,

6094 Plastic Covered Greenhouse, 4 sheets. 16'-0" or 26'-0" length, concrete pier founda-tion, 2" X 4" or 2" X 6" rigid frames = 4'-Q" o.c. with plywood gussets, for either plastic filmor rigid plastic,

6181 Home Greenhouse, 2 sheets. lO'-O" width X 12'-0" length X 7'-4" height to ridge,2" X 4" gambrel rigid frames, corrugated plastic cover. Reduced size plans available.

6185 28' Greenhouse, 3 sheets. 28'-0" width X 96'-0" length, 7'-0" eave, metal or woodtruss with 6/12 slope, double plastic film cover with air inflation. Reduced size plans available.

6197 Greenhouse Heating and Ventilating System, 3 sheets. Suspended gas fired unitheaters. Reduced size plans available.

6198 Soil Treating System, 3 sheets. Reduced size plans available,

6206 Hotbed, 2 sheets. Electric heating cable. (For Alaska install 2" rigid insulation onside walls and 2" rigid insulation 12" under soil). Reduced size plans available.

6251 Plastic Greenhouse, 2 sheets, 12'-0" width X 16' - 9-1/2" length X 5'-9" eave, straightwall and gable roof, 2 X 4 wall posts, gable roof sash panels with 1-1/2" thin wall conduit tie chords,Reduced size plans available.

734-286 Greenhouse Heating System, 2 sheets. Five 21' X 100' plastic greenhouses, centrallow pressure steam with condensate return pump, above ground steam and return, baseboardradiation or suspended unit heaters. Reduced size plans available.

NOTE: In heavy snow belt areas, the greenhouse roof must be supported in winter bycolumn at center, see SNOW LOADS, page 15,

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TABLE J LIST OF GREENHOUSE PUBLICATIONS

O1. J .W. Courter, Plastic Greenhouses, University of Illinois, Urbana, Illinois, Extension Circular

905, March, 1965.

2. H.E, Gray, Greenhouse Heating and Construction, Florist Publishing Company, 343 S, DearbornStreet, Chicago, Illinois, 1956,

3. M, Marshall, et al, A Gothic Greenhouse For Town and Country Homes, Virginia PolytechnicInstitute, Blacksburg, Virginia, Extension Circular 892, March, 1966,

4. J.W, Courter, A Simple Rigid Frame Greenhouse For Home Gardeners, University of Illinois,Urbana, Illinois, Extension Circular 880, April, 1964,

5. J .W. Courter, Home Greenhouses For Year-Around Gardening Pleasure, University of Illinois,Urbana, Illinois, Extension Circular 879, February, 1964.

6. R.J. Sheldrake, Jr,, Planning, Constructing, and Operating Plastic Covered Greenhouses,New York State College of Agriculture, Ithaca, New York, Cornell Miscellaneous Bulletin 72,June, 1966.

7. K.F. Baker, et al, The U.C, System For Producing Healthy Container Grown Plants, Universityof California, Manual 23 ($1.00).

8. J.N. Walker, et al, Painting Greenhouses and Greenhouse Equipment, University of Kentucky,Lexington, Kentucky, Experiment Station Bulletin No. 64-10-45,

9. Dr. Ray Sheldrake, Jr,, Air Makes the Difference, (plastic insulated by two layers of poly-ethylene separated by cushion of air), Dept. of Vegetable Crops, Cornell University, Ithaca, N ,Y ,

10. North East Regional Agricultural Engineering Service, Hobby Greenhouses and Other Gardening s~~^Structures, NRAES-2, price $2.00, Cornell University, Ithaca, N,Y. 14853, V_

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