The Q&A Archives: Fruit Flies Infestation Of House Plants

Question: I read your vinegar solution to the fruit fly problem; however, I have fruit flies in the soil of all 20+ of my houseplants (veggies, cacti, tropicals & trees). I've already tried a pesticide spray and that works for a day or two but then they come back. Could I add something to the soil that will kill the fruit flies or what should I do?

Answer: I suspect what you are seeing is a fungus gnat infestation rather than fruit flies. These pests will breed in moist soil so there are several things you can do to discourage them. First, avoid overwatering the plants. Allow the soil surface to dry out between waterings -- many plants actually do better with this type of watering regime. To facilitate this, (or if you have some plants that require an evenly moist or wet soil), simply layer about a half inch of coarse sand or fine gravel on the soil surface. This will drain quickly and dry out and make it impossible for the gnats to breed. In several weeks, as their life cycle progresses and the adults die off without reproducing, they should disappear. You can also use a soil drench for fungus gnats such as Gnatrol.

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