How to Get Rid of Fungus Gnats in Outdoor Potted Plants

Fungus gnats thrive in soggy soil.

Fungus gnats are tiny flying insects that look like small flies. They thrive in the damp soggy soil of potted plants and are often the result of infected potting soil or a plant from a nursery that had a fungus gnat infection. They occur in both indoor and outdoor plant pots, but are more noticeable indoors. Getting rid of fungus gnats in outdoor potted plants requires that you eliminate the damp soil conditions and trap the adults.

Things You'll Need

• Yellow sticky traps
• Bucket or pitcher
• Water
• BTI tablet
• Sand

Instructions

1. Stop watering the potted plant and move it to a covered outdoor location so that rainfall does not dampen the soil. Allow the soil to dry out for at least three or four days, which causes the adult gnats to leave.

2. Hang a yellow sticky trap on the potted plant to catch any adult fungus gnats that remain near the pot. Some sticky traps have stakes you can insert into the soil. These traps are available at any hardware store or garden center. Check the traps every two days, and replace them when they are full of insects.

3. Fill a bucket or pitcher with 1 gallon of water and insert a BTI tablet into it. The BTI tablet contains bacillus thuringiensis, a substance that kills fungus gnats. Wait until the tablet dissolves completely, and then water the outdoor pot with the solution until it runs out the bottom of the pot. BTI tablets are available at any store that sells pond supplies.

4. Spread a ½-inch layer of coarse sand on top of the potted plant to prevent any new adult fungus gnats from laying eggs onto the soil.

References

• Garden's Alive: Fungus Gnats -- Tiny Flying Houseplant Pests
• "Weekend Gardener" Magazine: Fungus Gnats -- Get Rid of Them Organically