Potted plants can be breeding grounds for gnats, especially the pesky fungus gnat. What's worse is that these annoying insects can be incredibly prolific during their rather short lifespans, generally only living a single week as an adult gnat. However, during this week, the gnat often lays up to 200 eggs. Needless to say, if left unchecked, your gnat problem could increase exponentially in a very short span of time. Thankfully, there are some relatively simple methods of dealing with gnats and protecting your potted plants.
Destroy the breeding grounds that attract gnats to your home and yard in the first place. Gnats tend to be attracted to moist organic material. So police your yard for any leaking faucets or rotting wood and tree debris. If the gnats never come around in the first place, then your potted plants have nothing to worry about.
Kill the eggs and larvae before they develop into adult gnats. Gnats like to lay their eggs in the top layer of soil of various potted plants. Dig up this top layer--generally about one inch down--and dispose of it. Be sure to replace the soil that has been removed with a fresh layer of top soil.
Use a family- and pet-safe form of garden insect insecticide on the potted plants. Spray it liberally on the plants as the directions indicate. This type of insecticide should be available at most stores with a home and garden section.
Spray the same family-safe insecticide on all window sills and door jams. This will help to prevent the gnats from making it into the house in the first place.
Blend a drop of lemon essential oil with a drop of lemongrass essential oil and then apply this mixture around the lip of the pots the plants are in. These oils will act as a more organic deterrent for the gnats in homes that do not wish to make use of insecticides.
Add 1 tbsp. of liquid dish soap to the watering container normally used to water the plants. The dish soap will repel the gnats and is safe for the plants it is being sprayed on.