Indoor plants aren't immune to pests. Small black flies, called fungus gnats, are minor pests, but they become a nuisance as they fly around the home. While these flies resemble small mosquitoes, they do not bite. Their larvae feed on plant roots and the lower leaves of plants, causing damage if the flies are present in large numbers. While chemical controls are available, manage them naturally by practicing proper cultural care of your houseplants.
Water the plants only when the top 1 to 2 inches of soil feels dry when you stick your finger in it. Overly moist soil, especially near the surface, provides an optimum breeding ground for fungus gnats.
Remove dead plant materials from the soil's surface, including fallen leaves. The gnat larvae feed on this material, so removing the food source minimises the gnat population.
Repot badly infested plants into sterile potting soil. Shake as much of the old, infested soil from the plant's roots. Cut out dead roots, then replant the houseplant into fresh soil. Dispose of the old soil outdoors so the gnats cannot reinfest the new pot.
Set a small pot of wheat sprouts near the infested plant, as female gnats prefer to lay their eggs in the sprouts instead of the houseplant. Dispose of the sprouts after three days, before the eggs have a chance to hatch. Repeat this every two weeks until the gnats are no longer a problem.
If plants are badly plagued by the small black flies, treat the soil with a Bt bacterial drench. This bacteria infects and kills the gnat larvae.