Houseplants are not immune to bugs merely because they are being grown indoors. Many types of insects, from fungus gnats to mealybugs, are common houseplant pests. New plants in the home are often the culprit, with insects hiding among the foliage or in the soil. Whenever you bring a new plant home, keep it isolated from your other houseplants until you can inspect it for pests and to allow any in the soil to hatch. Agents with Cornell University's Cooperative Extension Service recommend keeping new houseplants isolated for at least one month.
Insecticidal soaps are safe and effective for use on mealybugs, aphids, spider mites and whiteflies. The soap washes away the bug's protective outer membrane, which causes dehydration, eventually killing it. Insecticidal soaps are easy to make at home with regular dishwashing soap such as Ivory Liquid and Dawn Liquid or, for an organic solution, organic soaps such as Dr. Bronner's or Desert Essence. Combine two teaspoons of detergent with one gallon of water. Pour it into a spray bottle and apply it to both the top of the foliage and the undersides. Allow the soap to sit for an hour and then rinse it off with clear water. You may have to retreat the plant every week until the infestation is brought under control.
Horticultural oils essentially smother insects by blocking their breathing holes. It is especially effective when used on whiteflies, thrips and aphids. It is easy to make and any leftovers can be stored in the refrigerator. To make your own horticultural oil, combine one cup of vegetable oil and one teaspoon of dishwashing liquid. This is the insecticide base, so pour it into a jar or squeeze bottle for storage. When you are ready to treat a plant, pour one tablespoon of the oil mixture into a spray bottle and add two cups of water. Shake the bottle until the mixture is combined and spray the infested parts of the plant. The oil and water will separate, so shake the bottle frequently during application. Repeat the treatment every week until the bugs are dead.
Limonene is a substance found in the oils of many plant species, including citrus fruit. Lemon spray is a safe alternative to chemical pesticides for use on all houseplants, including indoor herb plants. Lemon spray is effective in the control of whiteflies, scale and mealybugs. To make lemon insecticidal spray, boil the peels of four small lemons in one quart of water for 10 minutes. Allow the solution to sit overnight, covered. Remove the peels from the water and add one teaspoon of organic soap. Pour the mixture in a spray bottle. Spray the infested portions of the plants until the insects are completely covered with the solution. Repeat the application in one week, if needed. Keep the plant out of direct sun immediately after treatment to avoid burning the foliage.