OCTOBER 6, 1997
Area Extension Agent
by Mary Robson
Cool nights bring refreshing sleep---misty mornings when the temperatures have dipped into the 40's really mean fall is here. But for tropical houseplants, temperatures dropping signal "winter." Many, such as schefflera, philodendron, and dieffenbachia, are native to tropical climates where they live as understory plants in tropical zone forests. Some may even defoliate when temperatures drop.
So it's time to bring houseplants indoors before they suffer cold damage, getting them settled back inside the house before the end of September. Any plant that has been summering outside should be carefully inspected and washed before it returns to the indoor world. Tip the pot up and look at the drain hole. Slugs and other soil-dwelling creatures like sowbugs will often set up housekeeping under the pot. Get rid of them.
Immersing the pot up to the rim in a bucket of water will also help to eliminate any soil-borne pests. Leave it submerged for about 6 hours, then let it drain thoroughly.
Inspect the leaves carefully for aphids, spider mites, mealybugs, and other hitchhiking insects or mites. Any resident population that survives on leaves and moves indoors will certainly multiply in warm, sheltered indoor conditions. Get a magnifying glass or hand lens to help with observation. Spider mites, a common houseplant pest, are no larger than the period at the end of this sentence. Their presence on plants causes a stippled, powdered look on leaves. Shine a flashlight into the plant to highlight fine, visible spider mite webbing. Mites have 8 legs, as do spiders, which makes identifying them simple once you have magnified them enough to see them at all!
Try washing the leaves thoroughly with water. If mealybugs and scale infest, wipe the individual pests off with alcohol. You may decide to use an insecticide. Be sure to get one registered for use on houseplants, and test a small area before spraying the entire plant.
Wear proper gloves, goggles, and long sleeves when treating houseplants. Registered houseplant insecticides contain chemicals such as insecticidal soap, horticultural oils, or pyrethrins which are derived from a natural botanical source, the pyrethrum daisy. If the plant must be treated to reduce a pest infestation, do the spraying outdoors. Let the leaves dry fully after applying insecticides before bringing the plant in. Don't use an insecticide for garden plants on the houseplant problems..
If a plant is severely infested, with twigs paved in scale (a frequent symptom on ficus plants,) or heavily laden with aphids or mealybugs, discarding it may be more sensible than bringing it indoors to infest other plants. Separate (or quarantine) all plants newly brought in for about a week for further examination before snuggling them next to your existing indoor plants.
As days grow darker, indoor plants also slow their growth. Water less frequently, and do not fertilize as often. When spring light returns, repot plants if needed and increase the fertilizer rate.
Poinsettias, the tropical plants that now symbolize winter holidays, should be brought inside and given careful management if bloom is desired for late December. One way to thoroughly appreciate the skill of nurseries is to attempt getting a poinsettia to set buds at home. Get started on this by the end of September to allow about 8 weeks of a strict light-dark routine.
Poinsettias bloom only after "short days." Arrange a routine that places the plant in bright light 8 hours a day, and in complete darkness for 16 hours the rest of the time. The dark period, which is managed in nurseries by using shade cloth to cut off all light, is vital. The dark should not be broken by flashes of light. Drop a light-proof box over the plant, or put it into an unlit room or closet. Keep it in the dark 16 hours a day from late September to about Thanksgiving. The plant should have begun to form buds which will open to the colorful bracts appreciated for the holidays. Once buds show, after Thanksgiving, stop the dark periods and simply provide as bright a light as possible during the day.
Keep the poinsettia warm. If the temperature in the house drops below 60 F, or it's drafty, the plant will suffer. Water regularly so that it doesn't dry out, and put it in the lightest place possible during its 8 hours of light. This process resembles managing a demanding pet. Even with success, the plant may not be as beautiful as one brought fresh from a commercial producer!