Bringing plants indoors for winter - Ask Extension
I have dozens of potted plants that I take outside every summer. What’s the best method for treating the soil and the foliage prior to bringing the ...
Knowledgebase
Bringing plants indoors for winter #920310
Asked October 20, 2025, 2:21 PM EDT
I have dozens of potted plants that I take outside every summer. What’s the best method for treating the soil and the foliage prior to bringing the plants indoors for winters so I don’t bring in insects.
Montgomery County Maryland
Expert Response
There is no practical or effective soil treatment, though if you are concerned about fungus gnats, you could use a product that is labeled for indoor use that controls the larvae with Bti. The linked page has more info, but it's basically the same ingredient used to treat water sources (like fish ponds) for mosquito larvae. Follow all product label directions for use, as repeat doses may be needed.
Which insects you are concerned about bringing in on the foliage or stems will determine what preventative measure to take. For most houseplant pest insects like aphids, caterpillars (mainly only on certain ferns), thrips, mealybugs, and whiteflies, plus mites, one or more topical sprays with either horticultural oil or insecticidal soap may help, but they need to contact the pest directly. (Do not use substitute ingredients like household detergents or soaps, which can damage the plant or not work as well.) If pests are not visible when a spray is applied, it will provide little benefit. Only a few insecticide ingredients labeled for indoor use have longer-lasting residues, but not all of them are safe to use in areas that may be accessed by pets or children. If a particular pest does appear later, feel free to share photos for identification and management recommendations.
The last-resort option would be to apply a systemic that is absorbed through the roots. How long the chemical persists in the plant's tissues is hard to predict, but might be several weeks at a time. Here too, though, if children or pets are around which might put leaves of any of the treated plants in their mouth, this approach would not be practical to try and potentially unsafe. (Similarly, if any of the plants coming inside are edible herbs or fruits like citrus, they might not be able to be treated with that type of product.)
Generally, the active ingredient used for systemic indoor treatments is imidacloprid, a type of neonicotinoid-class chemical. That group of chemicals may cause harm to pollinators if the residues persist in a plant that later flowers where pollinators can access it. (If it's something you were to treat late in winter and the plant goes back outside in spring and soon flowers, for example.) There are a couple products containing imidacloprid on the market that are specifically labeled for indoor use, as neonicotinoids are otherwise not legal in Maryland for someone who is not a certified pesticide applicator to use outdoors. In this context, the imidacloprid is in granular/pelletized form, sprinkled onto the potting mix and watered-in, where they slowly dissolve and the chemical is absorbed by the roots. Some insect pests have already become resistant to that ingredient, however, so if a treatment fails to prevent a pest outbreak, that might be why.
Miri
Which insects you are concerned about bringing in on the foliage or stems will determine what preventative measure to take. For most houseplant pest insects like aphids, caterpillars (mainly only on certain ferns), thrips, mealybugs, and whiteflies, plus mites, one or more topical sprays with either horticultural oil or insecticidal soap may help, but they need to contact the pest directly. (Do not use substitute ingredients like household detergents or soaps, which can damage the plant or not work as well.) If pests are not visible when a spray is applied, it will provide little benefit. Only a few insecticide ingredients labeled for indoor use have longer-lasting residues, but not all of them are safe to use in areas that may be accessed by pets or children. If a particular pest does appear later, feel free to share photos for identification and management recommendations.
The last-resort option would be to apply a systemic that is absorbed through the roots. How long the chemical persists in the plant's tissues is hard to predict, but might be several weeks at a time. Here too, though, if children or pets are around which might put leaves of any of the treated plants in their mouth, this approach would not be practical to try and potentially unsafe. (Similarly, if any of the plants coming inside are edible herbs or fruits like citrus, they might not be able to be treated with that type of product.)
Generally, the active ingredient used for systemic indoor treatments is imidacloprid, a type of neonicotinoid-class chemical. That group of chemicals may cause harm to pollinators if the residues persist in a plant that later flowers where pollinators can access it. (If it's something you were to treat late in winter and the plant goes back outside in spring and soon flowers, for example.) There are a couple products containing imidacloprid on the market that are specifically labeled for indoor use, as neonicotinoids are otherwise not legal in Maryland for someone who is not a certified pesticide applicator to use outdoors. In this context, the imidacloprid is in granular/pelletized form, sprinkled onto the potting mix and watered-in, where they slowly dissolve and the chemical is absorbed by the roots. Some insect pests have already become resistant to that ingredient, however, so if a treatment fails to prevent a pest outbreak, that might be why.
Miri
