Growing Plants Indoors: Pest and Disease Management

Growing plants indoors can be very rewarding. Learn how to nip problems such as pest insects and plant disease in the bud so indoor house plants can flourish.
By Helga Olkowski
August 3, 2012

“The Integral Urban House” is a comprehensive guide to achieving a completely sustainable urban lifestyle by creating a mini-ecosystem where residents grow their own fruits and vegetables, raise chickens, rabbits and fish, recycle 90 percent of their waste, solar heat their hot water and use a variety of other alternative technologies — all on a 1/8-acre city lot.
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Growing plants indoors allows you to pick ripe Chile peppers from the pot or snip fresh herbs at your convenience. Learn how to manage your indoor plants, and you can have a lush culinary garden at your fingertips. Prevent an aphid infestation, help plants bounce back from mold and solve other common indoor gardening problems in this excerpt from The Integral Urban House (New Catalyst Books, 2008). This excerpt from Chapter 9, “Raising Plants Indoors.” 

Growing Plant Indoors: Insect Pest Management

Because of the extremely simplified ecosystem, indoor plants may suffer from the lack of biological controls, that is, the predators that would keep plant pests in check in a more biologically complex environment. Insect pests may be even more difficult to control in the house than in the greenhouse, where lacewings and predatory mites can sometimes be maintained on a year-round basis.

The major pests indoors are aphids, scales, whiteflies, mealybugs, and mites. (These first four are all closely related Homoptera, producing honeydew.) The pest insects usually enter the home on the houseplant itself or are brought in with other garden materials and find their way to the house plants.

The first strategy you might wish to use when a few bugs appear is physical: handpick, squash, or rub them off. Cotton swabs or a small brush dipped in alcohol may help you to get into hard-to-reach nooks and crannies where the insects may be found. Washing the plant off in a mild soapy water may also help.

During late spring and summer, when plenty of general insect predators and parasites are found in the garden, putting the afflicted plant outdoors for several weeks may take care of the problem. Either the pests will be consumed, or, as with migratory aphids, the summer generation may fly away to another host.

Twice a small hot pepper plant that grows indoors on our kitchen windowsill and provides us spices for chili and beans has been infested in the early spring with an aphid (Myzus persicae). Infestation became obvious because the aphids’ honeydew (the sweet, sticky sugar protein excreted by many plant-sucking insects) began to shine on the leaves. We usually squished the first few aphids by hand, but invariably the aphid population escaped this control measure and began to spread. Usually by this time, the weather had become so mild that the plant could be set outside in a protected sunny spot on the porch. However, the aphid parasites and predators had not arrived in the area yet, so the pepper plant had to be hosed off vigorously each week. If this was not done, the plant began to turn yellow and drop its leaves. As the season progressed the biological controls appeared. First we would notice parasitized aphids among the colonies; then we would see syrphid fly larvae and adult lady beetles consuming their share. By early summer not an aphid was to be seen. Apparently all had either been eaten by insects or flown off to other hosts. The plant was then promptly moved back into the kitchen, where it lived without apparent insect companions until another spring. How did the aphids get there each year? Since there are a couple of early spring aphids in our area that can live on more than one species of plant, it is easy to see how a winged one might fly or be blown in through an open window or door.

Several years ago, aphids got started on this same plant quite late in the spring, and soon after we noticed their presence parasitized individuals became apparent. Not only had the aphid found its way into the house, but its parasites had too. Since none of the parasites’ parasites found the plant, the parasite proceeded to wipe out every last aphid, ending the problem for that year without our having to move the plant outdoors. But that event has not been repeated, perhaps because we are reluctant to leave the kitchen window open without screens because of house flies.

When moving plants infested with honeydew producers outside, you might wish to place them on stands with ant-excluders around the legs so that ants don’t prevent the aphid predators and parasites from doing a good job.

For bug-infested plants that are too large to move, handpick, or hose off, you can import predatory lacewings or mites just as in greenhouse pest management. After cleaning up the pest insects the predators will die off from lack of food, so for each new outbreak new predators will have to be imported. An excellent book on using biological controls on houseplants is Windowsill Ecology, by William Jorden.

What about using synthetic commercial poisons on house plant bug problems? We have expressed our thoughts on pesticides elsewhere. If you feel that a plant is so valuable that it must be saved at all costs, and have exhausted all safer methods of insect management, then be sure to select the least toxic material that will do the job. Move the plant outdoors, and wear a mask and gloves while handling the poison and treating the plant, washing yourself and your clothes afterwards. Remember, the house plants are supposedly being kept to increase your pleasure and health, not to add one more touch of poison to an urban environment already burdened with substances toxic to humans.

Growing Plants Indoors: Plant Disease Management

When plants look sick, and no insect can be found, the usual assumption is that it is being attacked by a pathogen. Plant diseases are harder to cure than either insect infestations or salt build-up (Another occasional threat to house plants—guests surreptitiously dumping unwanted alcoholic drinks into the nearest greenery—will not be dealt with here.) Read “Preventing Plant Disease” further along in this article as a handy checklist.

A last thought on maintaining house plants: they do grow best with attention. Whether this is a response to increased carbon dioxide from human respiration, to the caretaker’s alertness with respect to watering, bug management, and repotting needs, or to some relationship between humans and plants not yet satisfactorily explained, the authors are not prepared to guess.

Preventing Plant Disease

1. Do not overwater.
2. Do not overfertilize. (Excess nitrogen may encourage aphid infestations indoors as well as out, in addition to creating weak, oversucculent plants more susceptible to disease.)
3. If you or experts you are able to ask for advice cannot diagnose the ailment, try repotting the plant in fresh material.
4. Leaves infested with mold or fungus leaf-spots can be cut off and composted. Necrotic (black) areas on cactus can be cut out with a sharp knife. The cut area should be dusted with sulfur and the entire plant left to dry, out of direct sun, in a light, well-ventilated place until the wound has calyxed over.
5. Where crown-, stem-, or root-rot is the problem, it is best to destroy the plant. Avoid the problem in the future by not overwatering or overfertilizing, and by keeping water off susceptible plants.

Read more: Check out Is the Deep Litter System Right for Your Homestead? for more from The Integral Urban House.


This excerpt has been reprinted with permission from The Integral Urban House: Self-Reliant Living in the City, published by New Catalyst Books, 2008. 


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