What is the problem?
Fungus Gnats are tiny flying insects that are common in houseplants and seriously annoying to have around. While harmless to people, they are destructive to your plants and can reach plague proportions if not addressed.
Why do I have this issue?
Overwatering, or watering directly to the soil of your plants, especially indoors where the soil receives limited sunlight, means that the top soil cannot dry out and stays overly wet. Fungus Gnat eggs will hatch and thrive in warm and very moist soil.
Eggs and Larvae will have been transported into your home via the soil around new plant seedlings, or in some cases, in infected potting mix. Once the Gnats hatch and mature, they will rapidly spread to other nearby plants and lay new eggs in the top layer of potting mix.
How do I fix it?
If the infestation is new, let the soil of infected plants dry out completely, which kills the larvae. Be sure to water the indoor plants sparingly to avoid soggy top soil, or alternatively only water from below eg. directly to the reservoir of a self watering planter.
If the infestation is established then you need a 2 step approach.
- Remove adult Gnats
- Remove / Prevent Eggs and Larvae
To remove adult Gnats, consider making your own trap. Add a few tablespoons of Apple Cider Vinegar to a jar, and add 2-3 drops of concentrate liquid dish soap. The Gnats will be attracted to the vinegar and become trapped in the liquid. You can also add a small piece of ripe fruit to the trap to help attract them. For best results add a lid with small holes or a paper funnel to prevent them escaping.
There are various other techniques on the web, google it to find more.
To remove the Eggs and Larvae, scoop out the first 40-50mm (1.5-2 inches) of potting mix in affected plant containers and dispose of it. Replace this with fresh, good quality potting mix. For best results you can add some fine sand to the mix, or preferably spread the potting mix out thinly in the sun for a few hours to dry out before adding to your planter.