Pour one-quarter to one-half inch of apple cider vinegar into a clear or semi-opaque plastic cup, creating an effective fungus gnat trap. Add a drop or two of liquid dish soap and stir to combine thoroughly. Cover the top of the cup with transparent tape, leaving a one-eighth-inch opening in the center of the taped area.
Modify your watering practices. Allow the houseplant’s soil surface to completely dry out. Withhold water as long as you can without causing injury to the plant. Fungus gnats require a moist environment, so the larvae will die when the soil dries out.
Take the houseplant out of its pot gently if you have discovered fungus gnat larvae. Remove as much soil as you can without disturbing its roots. Seal the infected soil up in a plastic bag and discard it; do not add it to the compost heap. Clean and disinfect the plant container. Repot the plant in a good commercial sterilized potting soil mix.
Place the vinegar trap near your houseplant and check it daily. Don’t disturb it if you see gnats congregating on top of the taped area; they’ll soon find their way into the hole and down to the vinegar.
The presence of fungus gnats, or fruit flies, hovering in and near your houseplant is annoying. Adults are harmless to houseplants unlike their larvae, which can cause severe root system damage. Often drawn by unrefrigerated ripening fruit or even beer and fruit juice containers stored in recycle bins, these tiny flies seek the intoxicating essence of fermentation and are also attracted by damp areas such as household drains. Fungus gnats are particularly fond of depositing young in moist potting soil to feed upon fungi and decaying plant matter. However, instead of throwing the plant out, you can get rid of pesky fungus gnats using household vinegar.
Set up some yellow sticky traps around your houseplant to attract hovering adults to the area.
Cut a fresh raw potato into chunks. Place a few pieces on the houseplant’s soil for two or three days. Pick up the potato pieces and look to see if anything has been chewing on them.
How to Use Vinegar to Get Rid of Fungus Gnats on a House Plant
Remove debris and dead plant material from the soil surface daily to eliminate an adult fungus gnat attractant and larval food source.
Plants that are overwatered are susceptible to fungus gnats and their larvae can damage roots, but fortunately, vinegar works well in attracting the annoying pest.