Dealing with houseplant pests
Houseplant pest control combines close inspection, isolation of new plants, physical removal of pests, and careful use of soaps or oils. Check a plant for insects or disease before you buy it, then keep it isolated while any problems become visible. Water, rubbing alcohol, and pruning can remove pests, and horticultural soaps or oils are the chemical options named for houseplants. Soap and oil applications usually have to be repeated, and a plant that is heavily infested and badly damaged may be worth discarding. Read every label and follow the directions and precautions carefully.
When to do it
Start before the plant comes home. Look at the leaf axils and the undersides of the leaves for signs of insects or disease. Newly acquired plants are isolated for one to two weeks to allow any possible pest problems to become visible. New houseplants, and plants brought back indoors for winter, are isolated from other houseplants for about three weeks. Another figure given for new plants is six weeks apart from the plants already in the home. During isolation, examine each plant about once a week. Also check for pests whenever you water, fertilize, or clean a plant. If you detect pests on a plant, isolate it from your other plants.
What you need
A 10X (ten-power) magnifying lens lets you check the undersides of leaves. For washing, you need a bucket of tepid water for small plants and warm water to rinse both leaf surfaces. Cotton swabs and rubbing alcohol or isopropyl alcohol wipe off insects such as aphids and mealybugs. A soft toothbrush dipped in isopropyl alcohol brushes scale insects off. For heavier problems, you need a commercial insecticidal soap, or a horticultural soap or oil, used according to label directions. Do not mix homemade soap products, because they can burn plants. A solution of non-bleach household disinfectant is for washing previously used pots before you reuse them. All gardening tools and containers should be sanitized. Use pots with drainage holes and pasteurized potting soil. That soil has been heated to 180 °F (82 °C) for 30 minutes to kill most diseases, weed seeds, and insects.
Step by step
- Step 1
Check new plants before you bring them home
Look closely at the leaf axils and the undersides of the leaves for insects or signs of disease before you buy.
- Step 2
Keep new plants apart from your other houseplants during a quarantine period
Isolate newly bought plants for one to two weeks so hidden pest problems have time to show up. Growers isolate plants brought back indoors for winter for about three weeks. Some recommend up to six weeks of isolation for extra caution.
- Step 3
Examine isolated plants on a regular schedule
Check them for signs of pests or damage about once a week. Use a 10X magnifying lens so you can see small insects and eggs, especially on the undersides of leaves. Watch for honeydew, too: a shiny, sticky coating on leaves left by pests like aphids and mealybugs, which can lead to sooty mold.
- Step 4
Check plants for pests during routine care too
Look them over whenever you water, fertilize, or clean them. Isolate any plant where you find pests right away. Let the soil dry out between waterings too, since dry conditions kill fungus gnat larvae.
- Step 5
Wash smooth-leaved houseplants on a regular schedule
Wash them every two to three weeks. For small plants, turn the pot upside down and swish the foliage in a bucket of tepid water. For larger plants, rinse both the upper and lower leaf surfaces with warm water.
- Step 6
Wipe off soft-bodied insects by hand
Use a cotton swab dipped in rubbing alcohol to wipe off aphids and mealybugs, or dab each mealybug with isopropyl alcohol for small populations. Brush scale insects away with a soft toothbrush dipped in isopropyl alcohol, or scrape off early infestations with a fingernail. Test any treatment, including rubbing alcohol, on a small part of the plant first, since injury can take at least 48 hours to appear.
- Step 7
Knock pests off with a strong but gentle stream of water
Aim a fine, pressurized stream at scale insects, or direct a gentle stream of water right at mealybugs to dislodge them. Spray aphids outside with a strong stream of water or a soapy water spray, and cover the undersides of leaves. Repeated water sprays also help control spider mites. Misting for spider mites is best done outdoors so mites don't move onto another houseplant indoors.
- Step 8
Discard a plant that is too far gone
If spider mites heavily infest a plant and washing isn't working, discarding the plant is often necessary. A heavily infested, badly damaged plant is usually more economical to discard than to keep treating. Insecticides for aphids are rarely warranted, so try physical removal first.
- Step 9
Prune and remove damaged growth
Remove and destroy any leaves showing leafminer damage. Prune off infested stems and leaves to slow the spread of pests. Scale and mealybugs often need repeated, persistent treatments to clear up. Sanitize gardening tools and containers between plants to keep from spreading fungus gnats and other pests.
- Step 10
Treat stubborn infestations with horticultural soap or oil
A heavy scale infestation is best cleared by spraying with horticultural soap or oil, following the label instructions. These products are a good chemical option for houseplant pests when used as directed. Insecticidal soap is a contact insecticide, so it only works when it touches the insect directly. It has no effect once the solution dries on the plant. Read all label directions and precautions for the product you use, and follow them carefully. Repeat applications are usually necessary, since eggs and hidden pests often survive the first treatment.
Mistakes to avoid
Putting a new plant straight among your others skips the isolation that lets possible pest problems become visible. Spraying insecticidal soap and letting it dry is wasted effort, because the dried solution has no effect against pests. Soap works only when it makes direct contact with the insects. Applying it outdoors in direct sunlight, or to a plant under drought stress, is something to avoid. Mixing homemade soap products can burn plants. Skipping the small-area test also causes trouble, since symptoms of injury may take at least 48 hours to appear. Stopping after a single treatment falls short, because pests may be hidden or in the egg stage. Repeat applications of soap or oil are usually necessary to control pests. Misting for spider mites indoors lets the mites relocate to a different houseplant. Holding on to a plant that is heavily infested and badly damaged is a mistake, because discarding it is necessary and economical. Honeydew is a sticky excretion left by pests such as aphids and mealybugs, and it is a medium for sooty mold growth. Dry conditions kill fungus gnat larvae, so let the soil dry between waterings. Using imidacloprid on bee-attractive plants set outside during the summer is another mistake, since it is toxic to bees.
How this page was made
- Written with AI assistance from the sources listed on this page. AI is never the source of a fact.