If you notice little gnats flying out of your potting soil every time you water your houseplants or container garden, you have a problem with fungus gnats. While these small bugs can seem insignificant, they can be an irritation if you have plants indoors. Meanwhile, the gnats’ underground maggots may start to feed on your plants’ roots, causing damage and plant stress. Killing fungus gnats using a combination of cultural controls and insecticides can quickly render your potting soil gnat-free in a few weeks.
Reduce the watering of your potted plants to the minimum each plant needs. This gives the potting soil time to dry out between waterings, which kills the gnats’ maggots and begins to break the bugs’ life cycle. Because the gnats’ eggs hatch every six days, it will take a couple of weeks to fully bring the gnat population under control.
Turn and mix the top 1 to 2 inches of potting soil with a hand trowel. Repeat daily. This increases air circulation, hastens the drying of the top surface of the potting soil, and exposes the gnats’ larvae to the air, which in turn helps kill the underground gnat problem.
Tidy up your potted plants and container gardens, removing any organic matter from the soil surface. This includes fallen leaves, broken stems and similar matter. This organic debris harbors the gnats and also serves as a food source for the insects.
Place yellow sticky traps near the plant pots. The gnats are drawn to the yellow color and will get stuck and die. The combination of killing the underground larvae while trapping the adult gnats effectively disrupts their life cycle and eradicates the problem over the course of two to three weeks.
Apply a soil pesticide if your gnat infestation is so problematic that a few weeks of changes to your plant care and cultural practices doesn’t effectively remove the gnats from the soil. Common pesticides effective against soil gnats include acetamiprid and bifenthrin. Spray the pesticide onto the soil surface according to the pesticide’s manufacturer-specific guidelines.
Things You Will Need
- Hand trowel
- Yellow sticky traps
- Petroleum jelly
- Soil pesticide
- Chlorine bleach
- Gnats generally appear in your houseplants and container gardens due to potting soil contamination and unclean gardening tools, which can hide gnat larvae and gnat eggs. Always use sterile potting mix — if you’re using garden soil, bake it at 250 degrees Fahrenheit for 30 minutes to sterilize it — and rinse all pots and garden tools in a solution of 1 part bleach and 9 parts water.