With the onset of cool weather, it may be time to bring your non-hardy perennials indoors. Unfortunately, this is also a risky time of year for your plant collection because you run the risk of bringing pests indoors where they can infect your entire collection. Simple inspection is often not enough. In this guide, we will learn how to treat pests and keep them from ruining your houseplants as they come in for wintertime.
The presence of pests outdoors does not always manifest as a problem because they have the room to spread naturally. After all, they were designed to exist in nature. As houseplants, they are in an artificial environment. They are limited only to the plants you have in your collection. Whereas you may only get a few bugs on each plant outside, your favorite houseplant might have to support an entire population by itself. Aphids can be especially prolific, coating the entire surface of your plant. Although, we have been able to restore plants from these conditions using the methods in this guide, it is much easier to fight off the population before it explodes. This is especially true for flying insects that do not have wings until they mature.
Pests or even eggs can reside anywhere on your plant, including in the soil. They can be picked up in any environment, and nobody is immune to their wrath. It is important to know how to fight pests in all their hiding spots. Even careful inspection can fail to reveal them. But inspection is still a good place to start your battle. Many pests dwell on the undersides of leaves or in the nodes where the leaves meet the stem. Pests are especially fond of the new growth on a plant, so always focus your inspection there as well. Check up and down the stem for insects like scales. Chewed leaves are an obvious sign of some pests, such as whiteflies. Also be on the lookout for deformed leaf growth. While there are other reasons for this, it can also be a sign of insects. Remove the affected leaves as long as it is not one of the only leaves or does not apply to almost all of the leaves. Also be sure to scrape or pick off any pests you can.
Whether or not you spot pests, it is a good idea to rinse the plants thoroughly under a strong stream of water. Smaller plants can be placed under a running faucet for several minutes. Larger plants can be sprayed with a hose or put under a bathtub faucet. Be sure to concentrate on the undersides of the leaves and any crevice that could potentially house pests. This manual removal of the pests is often more effective than trying to kill them with pesticides, and it does not tend to harm the plant as long as you are careful. If you are lucky, this simple treatment may be all that is needed.
Now that your plants have been washed, and have no visual evidence of pests left, it is time to quarantine them. By keeping plants separated, it allows you to identify which ones may still be infected without any risk of a crisis among the entire population. If you only have a few plants, you can keep them in separate rooms. It is likely that flying insects would have been washed away by this point in the process so you do not have to worry about much cross contamination this way. If you have more plants than rooms, there is another approach.
Individuals in a large collection can be isolated by putting them in terrariums or humidity tents. A humidity tent is usually just a fancy way of talking about a clear plastic bag placed over the top of the plant and secured around the base of the pot with tape or a rubber band. As long as there are no gaps in the bottom or holes in the tent, it contains any infestation inside. Throughout the period that your plants are in the tent, it is important to give them regular doses of fresh air to avoid mold or fungus attacks or you will have an entirely new battle to fight.
After you have given the plants a few weeks to “incubate,” you will be able to identify which plants need further treatment. As we mentioned earlier, in a contained environment, it is more likely for a problem to escalate and reveal itself. It is ideal if you have a separate location to bring the infected plants to at this point just as an extra measure of caution. But you will be keeping them in their tents anyway until they prove safe to interact with the rest of your plant community.
Now that you have identified your problematic plants, it is necessary to provide further treatment for them. Since you have literally grown new pest specimens, you will want to go back to washing the plant. Change the humidity tent or sterilize it with rubbing alcohol and allow it to dry fully before reusing it.
There are a number of commercial pesticides, but we always recommend organic ones that will minimize damage to the plant and avoid introducing chemicals to your home environment. A sprayed solution made of cigarette tobacco soaked in water is effective in many cases. We have also had great success with Safer’s brand insecticidal soap. It works on a large range of pests. A concentrate is available, to which you add water and dilute it to a useable level. There are also various home recipes for insecticidal soap, which typically involve dish soap and canola oil. It is generally considered safe to ingest plant material that has been treated with insecticidal soap of this kind, as long as it is washed well. Insecticidal soap works by coating the bodies of insects and blocking respiration. The only drawback is that it must be applied directly to the body of the insect to be effective. This can be especially tough for plants that have numerous places to hide. Therefore, a regular schedule of washing the plant and applying the soap is usually needed until the problem disappears. You may even opt to make a bath and dip the plant inside if the battle persists. Before intermingling the plant with healthy houseplants, be sure to give it some time by itself without treatment, to see if the problem resurfaces.
A complete treatment of houseplants for pests includes treating the soil. We recommend diatomaceous earth for soil treatment. Diatomaceous earth is a highly absorbent white powder composed of the skeletons of algae-like organisms. The sharp surfaces of the particles act like glass to cut up the bodies of tiny insects. The absorbent power of the particles also sucks moisture from insect bodies. Some growers will mix diatomaceous earth in with their soil before potting. Others will water their plants with a solution of diatomaceous earth and water. However, the most common application is to put a layer of about ¼” across the top of the soil, leaving no spaces for bugs to surface without running into the diatomaceous earth. Diatomaceous earth may be sold as an organic pesticide. There is also a food grade powder, which can be used to kill parasites in the body. Diatomaceous earth is also used to filter swimming pools. Any of these will work fine. Once the diatomaceous earth has been laid across the soil, it has a tendency to absorb moisture from the soil and cake up. This is beneficial because it reduces gaps where pests might escape. It is best to water plants from the base of the pot rather than the top because you are likely to wash the layer away.
Many of us have lost prized specimens to pests. Hopefully, this winter we will all be better equipped to handle these situations. Pests can even be picked up in the house, especially as plant immune systems are reduced. It is important to provide adequate light to keep your plants in good fighting condition. Always remember to isolate and treat. Never leave a plant to be treated while it is still among healthy plants that can potentially be infected. Pests may be persistent. But if you are too, they really don’t stand a chance.