Gnats, especially fungus gnats, can plague your houseplants. The bugs not only eat away at parts of your plant and weaken it, but they may also create swarming clouds that can become a significant nuisance. Houseplant owners can use commercial insecticide sprays to quickly eradicate the gnats, but these products may rely upon potentially toxic chemicals. Individuals who want to avoid chemicals can take steps to kill gnats naturally using organic insect control techniques.
Pour a quart of fresh water into a plastic spray bottle. Add 2 to 3 tbs. of organic liquid dish soap. Close the spray bottle and shake it vigorously to mix the soap with the water.
Spray your houseplant with the soapy solution. Mist all exposed surfaces of the plants, focusing on new growth and stems where the gnats tend to congregate. The soap suffocates the bugs and kills them naturally, while coating the plant with a soapy residue that deters future insect pest infestations.
Dry out your plant. Gnats need moist conditions to propagate. Allow the surface of the potting soil to dry out to a depth of 1 to 2 inches between watering sessions. This kills the gnat eggs and soil-based larvae, breaking the insects' life cycle.
Add gnat-eating nematodes or mites, such as the Hypoaspis aculeifer mite, to your houseplant. Gnat-control predators are available as powders or vials for purchase from specialty garden stores and some nurseries. Nematodes prey upon eggs and larvae in the potting soil, while predatory mites attack mature gnats. Apply the predators according to the specific product's guidelines, as predator insect volume and concentration varies by product.
Build a gnat trap. Color a piece of white cardboard or paper with a yellow marker or yellow paint, a color that attracts gnats. Allow the cardboard or paper to dry, then coat with petroleum jelly or vegetable oil. Place the paper or cardboard near your affected houseplants. The gnats will fly at the yellow color and stick to the oil or jelly. Discard the trap when it is covered in gnats.