Introduction to Horticulture T - okcareertech.org...Introduction to Horticulture greenhouse Types The main purpose of a greenhouse is to provide an environment protected from extreme

Introduction to Horticulture

Unit 1 Introduction to Horticulture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 History of the Horticultural Industry • Classifying Plants • The Horticultural Tree Values of Horticulture • Standard Measures • Basic Formulas: Area and Volume Mix Ratios • Slope Ratios

Unit 2 Safety Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Accident Causes • Job-Safety Rules • Personal Protective Equipment

Federal Safety Code Colors • Types of Fire Extinguishers

Unit 3 Chemical Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Pesticides • Chemical Controls in Horticulture • How Chemical Controls Work

Types of Chemical Control Applications • Pesticide Poisoning • Types of Pesticide Exposure Chemical Safety Precautions • Pesticide Labels • Chemical Storage and Hazard Disposal Chemical Spray Equipment • Hazardous Material Classification

Unit 4 Hand and Power Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Hand Tool Safety • Hand Tool Uses • Hand Tool Maintenance and Storage

Power Tool Safety • Power Tool Uses and Safety

Unit 5 Growing Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 Structural Parts • Greenhouse Types • Frame and Covering Materials

Heating, Cooling, and Ventilation Systems • Benches and Beds

Unit 6 Plant Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 Plant Cells • Vegetative Structures • Monocots and Dicots • Reproductive Structures

Unit 7 Plant Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Plant Processes • Plant Growth Regulators • Plant Responses

Cultural and Environmental Factors

Unit 8 Plant Growth Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 Soil Formation • Soil Composition • Soil Particles and Texture • Soil Water

Soil pH • Plant Medium • Soil Media Materials • Soilless Mixtures

Unit 9 Fertilizers and Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Nutrient Requirements of Plants • Commercial Fertilizers • Application Methods

Fertilizer Storage and Handling • The Fertilizer Bag • Guaranteed Analysis of Fertilizers

Table of Contents

UPFRONT iii

Free sample provided by CIMC 800.654.4502 - www.okcimc.com

Unit 10 Greenhouse Watering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 Watering Systems and Equipment • Environmental Factors

Irrigating Greenhouse Crops • Watering System Fertilization

Unit 11 Plant Propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 Propagation Methods • Seed Germination • Methods of Seeding

Types of Available Seeds • Root Promotion in Asexual Propagation Methods of Asexual Propagation

Unit 12 Deciduous and Evergreen Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 Identifying Deciduous and Evergreen Plants • Plant Forms

Tree and Shrub Landscape Uses • Selecting Plants for Landscape

Unit 13 Cultural Practices for Trees and Shrubs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 Pruning Trees • Tools Used in Pruning • Care of Pruning Tools and Equipment

Pruning Schedules • Tree Structure • Pruning Specific Parts of a Tree Transplanted Stock • Transplanting Trees and Shrubs • Mulching

Unit 14 Plant Pests and Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 Plant Pests • Controlling Pests • Pest Treatment Safety • Integrated Pest Management

Unit 15 Landscape Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 Benefits of Landscaping • Elements of Design • Principles of Design

Selecting Plants for a Landscape • Steps to Develop a Landscape Design

Unit 16 Indoor Plant Care . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 Plant Containers • Hanging Baskets • Specialized Containers • Lighting Requirements

Repotting • Common Plant Disorders

Unit 17 Floral Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 History of Floral Design • Tools and Materials in Floral Design • Wire and Ribbons

Floral Containers • Color in Floral Design • Principles of Floral Design Elements of Floral Design • Floral Design Shapes

Appendix A – pH Availability Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269

Appendix B – Periodic Table of Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287

iv UPFRONT



Objectives

• Match structural parts of a greenhouse to their descriptions.

• Match types of greenhouses to their descriptions and pictures.

• Compare materials used for greenhouse frames and covering.

• Describe greenhouse heating, cooling, and ventilation systems.

• Identify characteristics of greenhouse benches and beds.

Key Terms

5UNIT growing Facilities

alloycontiguous greenhouseeaveebb and flow benchevaporative coolingeven-span greenhousefog coolinggothic greenhousegreenhouseground beds

hot water heatinfra-red heatinglean-to greenhousemovable benchesnatural coolingpurlinsquonset greenhouseraised benchesridge

ridge-and-furrow greenhouseroot zone heatsash barsolar heatingsteam heatunit heaters


60 UNIT 5 | GROWING FACILITIES

J ust as a car enthusiast can recognize models and makes of cars, a greenhouse worker can recognize common greenhouse structures and equipment. A greenhouse is a building with transparent walls and roof used for the cultivation of plants. Types of growing facilities and

related equipment vary widely. Greenhouses are built from many of the same basic designs, using common materials for construction. Choices for benches, bedding material, and heating, cooling, and irrigation systems are much the same throughout the industry. However, each greenhouse will have a different combination of characteristics.

Structural parts

Greenhouses are just like any house or building, a strong foundation is needed. A concrete footer is typically used as the foundation for the side posts, which are set three to four feet below the surface. Sidewalls are attached to the side posts and support the entire weight of the greenhouse. Along with the side posts, sidewalls also have side ventilators and curtain walls. The sidewall joins the roof at the point called the eave, which runs the length of the greenhouse.

The peak of the greenhouse is called the ridge. To support the roof of the greenhouse and hold the covering material in place, a sash bar runs from the ridge to the eave. There are multiple sash bars based on the size of the greenhouse. For added support to the roof, purlins run the length of the roof and give added strength to the sash bars.

Air movement is essential to providing a productive growing environment. For this reason, greenhouses are equipped with some kind of ventilation system. Roof and side ventilators allow air to enter the greenhouse during light rain, while shutters act like windows. Some greenhouses are equipped with a fan on one end and vent on the other to pull air through the greenhouse. The structural parts and type of greenhouse is greatly dependent on the climate conditions of the region.


Sidewall Side ventilator

Side post

Curtain wall

Concrete footing

Eave

Roof ventilators

Ridge

Sash bars

Purlins

Roof air ventsThinkstock Photos


UNIT 5 | GROWING FACILITIES 61


greenhouse Types

The main purpose of a greenhouse is to provide an environment protected from extreme temperatures, strong winds, heavy rain, and other damaging climatic events. Many types of plants can be grown in a greenhouse including vegetables or ornamentals. The type of greenhouse constructed depends on the space, money and purpose.

Even-span ContiguousRidge-and-Furrow

Quonset GothicQuonsetwith walls

Lean-to

An even-span greenhouse is a self-supporting commercial greenhouse and is the most common type of greenhouse. It is named an even-span because the distance from the ridge to the eave is equal on both sides.

Two or more even-span greenhouses connected at the eaves is called a ridge-and-furrow greenhouse. It contains supports but no inner walls separating the greenhouses. This allows for production of horticultural crops requiring the same growing environments.

Like the ridge-and-furrow greenhouse a contiguous greenhouse has two or more even-span greenhouses connected at the eaves. The difference is that a contiguous greenhouse contains inner walls separating the greenhouses which allows for production of horticultural crops requiring different growing environments.

Ridge-and-furrow greenhouseThinkstock Photos




A quonset greenhouse looks like an upside down half circle. The frame is made of laminated wood or bent pipe and is covered with polyethylene plastic. A quonset can also be found sitting on raised walls. A slightly pointed greenhouse covered with corrugated fiberglass is a gothic greenhouse. Gothic style provides greater load bearing strength to handle accumulations of snow.

A lean-to greenhouse is seldom used commercially and found attached to the south wall of a self-supporting structure. Lean-to greenhouses are typically used to start bulbs or seeds.

Frame and Covering Materials

Two things must be considered when designing a greenhouse frame: 1) the strength and weight of the materials, and 2) the amount of shade cast by the frame. Greenhouses must be strong enough to withstand wind and heavy snowfalls, and must not cast too much shade on plants below. Other factors to consider are the costs to build and maintain.

The frame of the greenhouse, which includes the perlins, sash bars and side posts, can be made of a variety of materials including aluminum, pipe and wood. There are advantages and disadvantages to each type.

Aluminum is a soft metal, and if used in its pure state, it would not be strong enough to construct a greenhouse. Instead it is combined with other metals to create an alloy. The aluminum alloy provides strength and flexibility along with rust and rot resistance, which is necessary for the humid conditions of a greenhouse.

For quonset type greenhouses, plastic pipe is often used to provide a frame. The pipe is typically bent into shape and wrapped with flexible plastic covering. This is an economical method for framing a greenhouse; however, pipe is not sturdy enough to withstand other greenhouse styles and covering materials.

Quonset greenhouseThinkstock Photos

Lean-to greenhouseThinkstock Photos

Thinkstock Photos




Another common framing material is wood or wood-metal combination. Wood used in any greenhouse must be treated with preservatives due to a short lifespan under greenhouse conditions. Wood can decay due to fungi that grow and feed on the wood. Moisture, warmth and air – all conditions within a greenhouse – promote the growth of fungi. Cedar, cypress and redwood are typically used due to their rot resistance. Wood is initially economical to use but may need to be replaced over time due to decay.

Some greenhouses use a wood-metal combination for framing. Iron or steel is used for supports with wood sashes to hang the glass or covering material. Any metal should be treated prior to use to prevent rusting. This could include galvanizing or painting to coat the metal.

After a greenhouse is framed, it must be covered to create an enclosed environment for plants. Plastic and glass are the materials most commonly used to cover greenhouses due to their transparency. All types of covering materials have advantages and disadvantages. It is up to a producer to determine which covering best suits his or her growing needs.

Glass is the best type of covering material for transmitting light to plants. Many conservatory type greenhouses use glass because of it appealing aesthetics. For a long-term investment, glass is the most economical, but it is expensive in the initial installation. It also is easily broken and must be replaced, which is an added expense.

Plastics can come in flexible or rigid forms. A flexible bubble plastic, such as the type used in packing boxes, can cover a greenhouse and provide some insulation. It is inexpensive to install; however, it may not last as a long-term use product. Other flexible sheet-type plastics, such as polyethylene, are used. These pass less light to the plants than glass and are usually considered temporary. They are the least expensive in the short term, but they turn yellow and become brittle, needing replacement in one or two years.

Rigid plastics, such as fiberglass or polycarbonate, also pass less light to the plants than glass. When compared to flexible plastics they will last longer, 5-25 years, depending on the specific materials, but will eventually yellow and weaken. These plastics can withstand the weather elements better than sheet plastic and have less of a chance of breaking compared to glass.

Thinkstock Photos




Biological Systems and Agricultural Engineer

Today’s agriculture is more than cows and plows. It has evolved to light-controlled greenhouses, GPS systems on your tractor to no-till farming. All these practices have changed the way people look at and work in agriculture, and biological systems and agricultural engineers are the ones who continue to create these new, more efficient tools and methods.

Biological systems and agricultural engineers study engineering, physical sciences and biological sciences. They are versatile and work in a variety of areas ranging from the building design industry, the food processing industry, the farm implement industry to the environmental industry. Some agricultural engineers design buildings for animals, equipment, storage or plants. Those in the food processing industry work in all areas of the food industry from farm to table. They may create new ways to monitor the inside of a commercial oven or even design new transportation methods to keep food safe when being delivered to the store. Those in the farm implement industry design equipment such as balers, combines, sprayers and planters. They develop new ways to make farming more safe and efficient.

Engineering jobs are available in about every industry in the country and world. Engineers can work as consultants for private industries or work for government agencies, universities or agricultural experiment stations.

To become an engineer, one must have at least a bachelor’s degree from an accredited engineering school. Many jobs require a master’s degree or Ph.D. The average salary for those in an entry-level engineering position is $42,000 a year, while those with more education and experience can make between $60,000 and $75,000 a year.

If you’re interested in becoming a biological systems and agricultural engineer, begin taking classes in math, biology and physical sciences. If you choose to become an engineer, one day you might be responsible for developing a new type of technology used in agriculture.

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Heating, Cooling and Ventilation Systems

The method of heating and cooling a greenhouse will depend on the intended use and the availability of utilities. If only bedding plants are to be sold in the spring, there is no need to install a summer ventilation system. If you are planning on growing all year long, a heating and cooling system will be required. There are many ways to heat a greenhouse, but not every method is safe, reliable or easy to use.

Some people heat with wood burning stoves, but not many people will stay up all night to keep a wood stove burning. Some of the most common methods of heating include unit heaters, hot water heat, root zone heat and steam heat. Unit heaters also call forced-air heaters, have three major parts: a combustion chamber, a heat exchanger, and a blower. All of the parts are enclosed in one unit and can be independently replaced or repaired. The grower has the option of locating the heater wherever he or she chooses. Natural gas or propane is required to operate this heater, and electricity is needed for the blower to operate. Heaters are available in different sizes and energy efficiency ratings. This is the most common method of heating.

The hot water heat method uses recirculated water that is heated to 160-180° F and then pumped through a system of tubes or pipes. As the water circulates through these tubes it gives off heat, and the greenhouse environment is warmed. The grower has the option of running tubes along the greenhouse walls, in the floor, or on the benches. If the heat is put on the bench, rubber tubes are used. If the heat is placed along the walls, aluminum fan radiators are typically used. Small scale boilers are good for heating the water. There are also European type tankless water heaters on the market, and they have been used with success. Generally, typical U.S. water heaters will not work because they heat too slowly. With the boiler system, several greenhouses can be heated with one unit. Boiler systems do require maintenance and are initially expensive. Tankless water heaters are less expensive, require less maintenance, but are not as long lived as a boiler. Tankless heaters do provide the grower with some protection since the entire range is not heated with the same heat source. If the boiler breaks down there is no heat in any of the greenhouses. If a tankless heater goes down, only that greenhouse has no heat. Natural gas and propane are the best fuels for boilers, but coal, oil or wood will also work.

Root zone heat is a unique name for hot water heating that places rubber tubes on the bench in intimate contact with the root zone of the plant. This is an economical method because only the area near the plant is heated and not the entire greenhouse environment.

Greenhouse heaterThinkstock Photos




A steam heat system works on the same principle as hot water heat, but steam is circulated through the pipes. These pipes may only be placed along the walls or floors and not directly on the bench. Water must be heated to 212- 215° F to produce steam, and the steam is then circulated through the greenhouse. Heat is released and the steam condenses to water and is then reheated. This method of heating requires large boilers and someone who is knowledgeable of their operation. Very few greenhouse operations find steam heating an economical method.

Infra-red heating warms solid objects like plants, employees and benches but the air is not heated and remains cool. This system of heating was originally predicted to be very energy efficient since the entire greenhouse environment is not heated. These heaters are expensive, require a lot of maintenance and are short lived, so they have not gained widespread use.

A solar heating system traps the sun’s radiant energy in water filled solar collectors. This heat is released into the greenhouse by running the hot water through tubes in the greenhouse. This system is basically a hot water heating system that uses the sun as the heat source. Unfortunately, solar energy technology has never been completely developed. There are a few greenhouses that use solar heat for a portion of their heating needs, but it is not total heating system.

These heating methods represent the basic heating systems a greenhouse grower can choose. Regardless of the method there are a few rules to be followed. Always vent the exhaust from the heater. If the combustion process is not complete, carbon monoxide and/or ethylene will be released into the greenhouse, and plant growth problems will occur. The exhaust stack should be at least 8 inches above the highest point of the roof to insure adequate venting. If a power vent is used, this rule can be ignored. A power vent is an exhaust stack that has a fan built in to force the exhaust outside.

The air inside the greenhouse must be stirred while heating, which is generally done running the length of the greenhouse. The warmed air is pulled into the fan, blown through a tube, and mixed evenly throughout the greenhouse. The fan jet is usually mounted near the heater so the warm air can be drawn in and evenly circulated in the greenhouse. One of the newer systems uses several fans but does not use a perforated plastic tube.

Plastic ventilation tubeCIMC Photo




Plants do not grow well if temperatures are too hot or too cold; so cooling a greenhouse is just as important as heating. The only way to cool a greenhouse is to fill it with cool air from outdoors. But, if the outdoor temperature is 90° F there won’t be much of a cooling effect. Greenhouse growers have learned that if water is evaporated from a surface the air temperature is lowered. Because of this the evaporative cooling system was developed and is the most widely used cooling system in greenhouses.

Evaporative cooling, also called fan and pad cooling, is the most commonly used system in the greenhouse industry. This system uses a pad that absorbs water and exhaust fans to pull air through the pad and greenhouse. This pad must be capable of absorbing water, drying out and then rewetting. Originally, the pad was composed of aspen or shredded wood, but this material only lasted one season. Today pads are composed of treated paper that lasts several years. Pads are installed so that water is dripped on top of the pad and the entire pad system stays wet. The exhaust fans, located on the opposite end of the greenhouse, are controlled by a thermostat.

When the interior of the greenhouse becomes too hot, the thermostat causes the cooling system to begin operating. The vent door opens, water begins to drip on the pad and the exhaust fans come on. Air is pulled through the pads and exits through the fans. The air that comes through the pads is cooled by evaporation and replaces the hot air in the greenhouse. The greenhouse remains cool because the fans run continuously and pull newly cooled air inside. Evaporative cooling works well in areas where the outside humidity levels are low. When the outside humidity levels become high, evaporative cooling is not as efficient.

A natural cooling system replaces the air inside a greenhouse with outside air. The outside air may be pulled in by a fan or by natural breezes. This method of cooling is only effective in the early spring when the outside air is cool or in climates where the summer temperatures remain low.

Fog cooling is a newer modification of the fan and pad system in which pads are eliminated. Fog nozzles are installed throughout the interior of a greenhouse and emit a fog. As the fans pull outside air in, the fog evaporates and the air temperature is lowered. Applying shade also reduces the interior air temperature a few degrees but will not cool the greenhouse. This treatment also lowers the light intensity and should not be considered a cooling system.

Thinkstock Photos

Evaporative cooling padCIMC Photo




Benches and Beds

There are many bench types routinely used in greenhouses. Some are commercially available, and many more are designed by innovative growers to fit their own special needs. The most commonly used types are raised benches, ground beds, movable benches, and ebb and flow benches. Producers also often do not use benches at all to store their plants.

Raised benches are those that are raised off of the floor, generally 24 to 36 inches. This is a convenient working height for employees and a comfortable shopping level for customers. The grower has the option of adjusting the height to suit his or her plan.

Ground beds are benches that are constructed directly on the floor and filled with media. These beds are usually 6-8 inches deep and the crop is grown directly in the media. This bench type is mainly used for cut flower production, and only a few growers still use this system today.

Movable benches, also called rolling benches, are a specially designed raised bench that is made to roll sideways. The legs and frame of the bench are stationary but the bench top slides left and right. These benches were introduced in the mid 1980’s and are gaining popularity because they eliminate the need for several aisles in the greenhouse. Movable benches are the most space efficient. With these benches the grower only needs to leave one aisle open for worker access. If the employee needs to get to the middle of the greenhouse, they simply slide the benches over until the walkway is in the desired location. Rolling benches are commercially available in galvanized metal and are generally built to run the length of the greenhouse.

An ebb and flow bench is another type of raised bench that is approximately 3-6 inches deep and capable of holding water. The growing containers are placed on the bench as usual and when the crop needs irrigation, the bench is flooded with water. The pots sit in this 3-6 inches of water and absorb moisture through the bottom. When the pots have been thoroughly watered, the plug is removed and the water drains from the bench into a storage tank. These benches are becoming very important in areas of the country where waste water must be reduced. Ebb and flow benches are commercially available and some manufacturers produce rolling ebb and flow benches.

Some producers choose to grow bedding plants directly on the greenhouse floor; however, few potted plants are grown this way. This is an unsanitary method that causes disease problems and poor plant growth. The grower places the pots and flats in groups on the floor as if they were

Wood and wire mesh benchThinkstock Photos




on a bench. This can create unpleasant working conditions for employees and is unappealing to the customer. It does, however, save the cost of constructing or purchasing benches.

Greenhouse bench construction is limited only by the imagination. A grower interested in the rolling or ebb and flow systems will generally purchase them. There are other pre-made benches commercially available but many growers choose to construct their own. Some of the materials commonly used in bench construction include concrete blocks, wood, wire mesh, expanded metal, and metal piping.

Concrete blocks are universally used as the legs of any raised bench. They are durable, inexpensive and can be easily moved and reassembled. A wooden or metal frame is constructed and then some type of small mesh wire or expanded metal is nailed or welded on top of the frame. Wooden pallets can also be used as beds. They provide a very strong bench top and can usually be obtained free of charge.

The benches in a greenhouse are usually arranged in one of a few different patterns. Parallel benches run the length of the greenhouse and have several aisles. This method is not space efficient. The peninsular bench arrangement has one major aisle in the center of the greenhouse. Other short aisles run perpendicular to the center aisle. This arrangement is more space efficient than parallel benching.

Thinkstock Photos

Plants grown on the greenhouse floorThinkstock Photos

Parallel Bench Arrangement

Peninsular Bench Arrangement

Parallel Bench Arrangement

Peninsular Bench Arrangement




Unit Summary

With the right temperature, moisture, humidity and sunlight, plants can thrive. Greenhouses are the ultimate growing facility for plants because all conditions can be regulated and adapted to fit the needs of a variety of plant species. All greenhouses are made of basic structural parts; however, not all greenhouses have the same parts. The parts depend upon the type of greenhouse built. A producer determines the type of greenhouse that best suits his or her needs. Along with determining the type of greenhouse, producers must also know if a heating or cooling source is needed in the greenhouse. Climates in the north may not need a cooling system; rather ventilation is used to bring in cool air from outside. The producer must also choose which type of bench system fits his or her growing needs. Many plants can be grown directly on the ground, but if the greenhouse is used for retail sale, the producer may want benches to allow for shopping ease of customers. With the right preparation and selection of materials, a producer can use a greenhouse for many years and grow a variety of plant species.

Unit review

1. What is the difference between an eave and a ridge?2. What do the sash bars and perlins do for the the greenhouse structure?3. Why might a producer choose a contiguous greenhouse over a ridge-and-furrow?4. What advantage does a gothic greenhouse have over a quonset?5. Name the types of materials used in greenhouse framing.6. Outline the advantages and disadvantages of greenhouse covering materials.7. Why are unit heaters the most common heating method?8. When might a producer choose to use root heat rather than heating the air?9. Why has solar heating not caught on as the sole heating system in a greenhouse?

10. What is the purpose of a pad in evaporative cooling?11. When is natural cooling the best method?12. Compare the advantages and disadvantages of raised benches and no benches.


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Introduction to Horticulture T - okcareertech.org...Introduction to Horticulture greenhouse Types The main purpose of a greenhouse is to provide an environment protected from extreme