Fungus Gnats on Indoor Plants

Q. I have noticed tiny dark insects flying around my indoor holiday plants. What are they and will they damage these plants?

A. Fungus gnats are tiny insects often seen hovering above moist soil of indoor plants. They are attracted to damp soil mixes that contain peat moss or shredded pine bark where they lay their eggs. The developing larvae tunnel into plant roots or small cuttings and seedlings where they can do extensive damage, particularly in greenhouse propagation situations. To reduce the gnat population, change the environment they prefer: avoid overwatering indoor plants; space your plants farther apart if they share the same pot; reduce the use of high-nitrogen fertilizers, especially in winter; and allow the top inch or two of soil to dry out before watering your plants. Some gardeners cover the soil with an inch of sharp sand to deter egg laying. Insecticides are available for professional greenhouse use but are not normally recommended for the occasional home problem.