Over-Watering Indoor Plants & Gnats

Overwatering plants can attract gnats.

The nonbiting fungus gnat is most often found around indoor plants that have been overwatered. These gnats feed on fungus that grows on plants such as the salvia or geranium. Fungus gnats are pollinators that feed on decaying organic matter. Although they're an annoyance, the adult gnat does little harm. Instead, it's the gnat's larvae that causes trouble.

Overwatering

The process of overwatering an indoor plant simply means the amount of water provided to the plant exceeds the amount of water it can absorb. When this happens, the excess water remains on the soil, creating favorable breeding conditions for gnats. Gnats thrive on rich, moist soil, where larvae can feed.

Identifying Gnat Invasions

The most common way people find gnats have invaded their plants is when they see an adult gnat fly out of a plant or gnats swarming around indoor plants. To confirm the invasion, look for signs of the gnats' presence, such as a small, narrow slime train in the soil. In some cases, you may also find the larvae, which are white with a black head and can be about ¼-inch long.

Life Cycle

An adult gnat has a short life of about one week. Though they do not live long, they can lay up to 200 eggs in that time. The larvae will hatch after four days, feed off your plants for two weeks, spend three to four days as a pupae and then become an adult. Because the larvae are small and hard to detect, gnats can cause plenty of damage to houseplants before you know they've entered your home.

Problems

Because adult fungus gnats don't bite, they're mostly harmless to humans and plants. Larvae, however, feed on the roots and root hairs of plants, This can cause root rot. Larvae can also get into the stem and leaves of a plant, causing it to wilt.

Prevention

To prevent fungus gnats, do not overwater indoor plants. Let the soil dry. Keeping it well drained destroys the gnats' breeding ground. Consider using a fungicide, as this will remove the gnat's food source. Screen and caulk leaky windows or areas where adult gnats can enter a home. If necessary, use yellow sticky traps on the soil surface to catch adult gnats before they lay their eggs.

References

• Do-it-yourself Pest Control: Fungus gnats
• Oregon State University: Do your potted plants have fungus gnats