Gnats are attracted to houseplants, and they will often lay eggs in the top 2 to 3 inches of the potting soil. The gnat larvae feed off organisms in the potting medium and they can destroy the plant roots. Gnats also spread diseases and fungi that will damage the houseplant. Kill the gnats to keep them off your houseplants so that the plants remain healthy. If you do not kill the gnats, they will continue to multiply and infest the houseplants.
Allow the top 2 inches of the soil to dry between each watering. Letting the soil dry will slow the growth of fungi and kill larvae in the soil. Gnats are also attracted to damp spots so they can lay their eggs. The dry soil will discourage them.
Combine 2 tbsp. of organic liquid dishwashing soap with 1 qt. of water in a spray bottle. Shake the bottle and spray the plant with the solution. The soap will suffocate the gnats, kill them and coats the houseplant with a residue that will keep the gnats away from the foliage.
Remove the top 3 inches of soil when you notice a heavy gnat infestation. Remove the soil carefully so that you do not destroy the roots. Replace the soil with fresh, sterilized potting soil and then add a thin layer of peat moss.
Fill a bowl with white distilled vinegar. Add two to three drops of dishwashing soap and place the dish near the plant. The vinegar attracts the gnats but they will drown due to the dish soap. Change the solution periodically when it fills with the gnats.
Purchase commercial sticky traps. Hang the traps next to the houseplants to capture the adult gnats. Replace the non-toxic adhesive traps when they become covered or unsightly.