Fungus Gnats

March 1, 2016

I read in your column about the problem of tiny flies in the dirt of flower pots. I have misplaced the article and we are over run with the pests. Would you please tell me what the solution was for getting rid of them?

Fungus gnats are what you are referring to. If you have gnats I would say you are probably overwatering. Fungus gnats are more of a nuisance rather than a detriment to your plants. The small larvae are in the soil and are feeding on the fungi growing in the potting soil, along with some small roots. Fungus gnats are more abundant in old, moist potting soil. As they mature, they turn into small gnats that hang around on the surface of the soil or fly around the plants, especially when the plants are disturbed. Since fungus gnats multiply more rapidly in moist soils, keep your plants on the dry side.  Especially during the cooler, winter months when houseplants aren’t growing very rapidly water no more than once every two weeks for most plants. Frequency of watering will vary by plant type, container size and how hot you keep your house. Top-dressing the soil with sand, using a yellow sticky traps to trap the adults and prevent them from laying eggs, and if they continue, you can drench the soil with an insecticidal soap or BT product.

January 2012

I always repot my plants in the fall to bring around 4 in my house. I repot because my brother brought 11 baby copperheads in the house one fall. Anyway, I always get gnats, several hundreds of them come out of my plants so therefore I have to move them to the garage and cannot enjoy my plants in winter. Do you know what I can do to avoid the gnats? I always buy good soil.

Wow! And I thought the snake story was an urban legend! If you have gnats every year, I would say you are overwatering. Fungus gnats multiply more rapidly in moist soils. Especially during the cooler, winter months, houseplants would benefit from being on the dry side—usually no more than once every two weeks for most plants. Timing of course will vary by plant, plant and container size and how hot you keep your house. Top-dressing the soil with sand, using a mild insecticidal soap drench when you move them inside can also help.

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