Fungus gnats prefer warm, moist environments. Remember, only water houseplants as needed rather than on a regular schedule to avoid oversaturating plants and creating a fungus gnat haven. Determine if the plants need water by inserting your index finger into the soil about one inch. If the soil is dry, it’s time to water. During winter plants tend to use much less water so you can expect to be watering less frequently than during the summer. Dump water out of the saucer once it drains so plants are not in standing water.
If fungus gnats are already present in your plants, allow the soil to dry at least through the upper three inches. You may even consider repotting the plant in fresh soilless media. Remove as much soil as possible from the plant roots to eradicate the eggs and larvae of the gnats.