Indoor Plants

Environmental factors affecting plant growth

• Light - most houseplants are understory plants• Water – very tricky• Nutrients- match to the needs of the plant and time

of year• Temperature – warmer days cooler nights ( tropic to

subtropic) • Air – clean, not too dry

LIGHT/ Photosynthesis

• Light descriptors: intensity, duration, quality• All green living plants need light to grow• When grown in too little light plants will be

etiolated (spindly)• The brighter the light the more color develops

in leaves ( coleus, begonia)• Flowering usually depends on light levels and

day length

Light intensity

• Light intensity is measured in Foot Candles, Lux or Lumens. 1 foot candle is the light cast by a standard candle at the distance of 1 foot.

• Light intensity influences:– Photosynthesis– Stem length– Leaf size and color– flowering

Light Intensity

• Factors that influence intensity of sunlight– Curtains, trees in the landscape, uv filters on

windows, weather, season, cleanliness of the glass, low E glass, paint color of the room…

– Too much light can sunburn a plant

Houseplant classification

• Houseplants are listed as High, medium or low light, and some plants can be in several categories.

• In a Duluth house, the south windows with have the strongest sunlight, E and W = 60% and N=20%

• The southern exposure also generates the most heat followed by W, then E, then N

Light Duration

• Most plants need some darkness at night 3-4 hours.

• If the light in the house is a bit low longer hours of illumination can compensate.

• Plants are generally divided into long day, short day and day neutral when describing initiation of flowering

Light Quality= wavelength

• Photosynthesis required red and blue light• Sunlight has all the right parts of the spectrum• Electric lights may or may not– Incandescent lights lack blue, and add too much

heat– Fluorescent “Grow lights” are more expensive

than they are worth– Cool white fluorescent or a mix of cool white and

warm white are the best deal – 12 “ above plants

Coping with low natural light

• Choose “low light” plants: Philodendron, Pothos, Aglaonema, Cast Iron Plant

• Rotate your plants into the better lit areas for a few weeks to rev them up

• Put plants outdoors in summer in a “bright indirect” light place

Watering

• Let your plant tell you- Observe closely and the plant will let you know when it is at “incipient plasmolysis” ( the leaves turn a little dull colored)

• Check the weight of the pot, lighter=less water in the soil.

• Scratch the surface if you see no damp soil down ½ inch, it may need watering

Watering

• Plant roots do not function when a plant is overwatered ( the roots need Oxygen)

• Symptoms of over or under watering:– Lower leaves and scattered leaves turn yellow

from root rot ( over watering)– Oedema ( corky bumps on the leaves) usually on

succulents when the plant is overwatered– Adventitious roots on the soil surface =

overwatering

Watering

• Leaves will wilt if the plant is in dry soil OR in saturated soil

• Letting plants wilt then snap back when watered can cause slow growth, flower drop and leaf drop.

• Make sure you have drainage in the pot- a hole in the bottom. Don’t let the pot sit in water ( in a full saucer)

WateringThe general rules

• use air temp water• water until excess water comes out the

bottom of the pot, then dump out the saucer.• Don’t use softened water• Some plants are bottom watered, however

you should remove the pot once the wetness reaches the surface of the soil

Potting Soil

• Potting soil needs more air than garden soil• A good mix contains a combination : peat,

vermiculite, perlite, compost , sand, loam• Soil mix may contain nutrients ( plant food)

but that will be used up in a month.• If your mix is mostly peat, it can shrink away

from the sides of the pot and be heard to re-wet.

Nutrients

• Plants make their own food from photosynthesis but they need a source of essential minerals. You will learn these later.

• Most house plant fertilizers are water soluble salts

• The label recommendations are usually too strong so use ½ of the label directions.

• Fertilize most houseplants in spring and summer only

Nutrients

• Time release fertilizers will last for several months

• ORGANIC fertilizers take longer to become available in the soil and less likely to “burn”.

• INORGANIC fertilizers are immediately available to the plant but more likely to burn.

• Only fertilize when plants are actively growing.• Don’t fertilize a bone dry pot

Fertilizers are salts.salts can accumulate in potted plants

• If you see a whitish or yellow crust on the surface of the soil it is probably a salt buildup

• You can scrape off the top ¼ to ½ inch of soil and replace with fresh soil.

• You can leach the soil in the pot with fresh water to remove excess salt( run water through the pot).

Temperature

• Most house plants like people temps 75 day and 65 night, most can adapt a few degrees either way.

• Respiration (burning food) in plants happens 24hours a day and high temps speed up the process. Light allows photosynthesis to make more food.

• Houseplants suffer when they have low light and high temps

Temperature

• Most flowering plants will have higher qualit flowers if they have cooler nights (55-60)

• In Duluth the temps next to a window can be quite cold on a winter night, you may have seen house plant leaves frozen to a window.– Move plants farther into the room and off a cold

floor

Cleaning plant leaveslets in more light

• The leaves will get dusty• Wash with warm water and a soft sponge• Don’t use wax products or mayonnaise

Air quality

• Plants use CO2 and O2• Air circulation is beneficial• Gas leaks can kill plants, products of

incomplete combustion ( ethylene) can make houseplants grow strangely or drop flower buds

• If all your plants twist up at the same time –– It could be an air quality problem

Insect pests

• Observe plants closely• Prune the worst looking parts of the plants• Spray plants with products that won’t kill you

or your pets, insecticidal soap, Ivory soap, alcohol

• Keep checking the plants because insect eggs are usually un affected by sprays