How To Keep Fungus Gnats Off Your Houseplants
Fungus gnats are a common and frustrating problem for anyone who keeps houseplants. These tiny flying insects often show up in damp soil, laying eggs that turn into larvae, feeding on roots and organic matter. While they don't usually harm mature plants, they can weaken seedlings and become a constant annoyance. Thankfully, there are several ways to prevent and remove them without harming your plants or bringing harsh chemicals into your home.
Water Less Often
Fungus gnats love moisture, and overly damp soil is their favorite place to lay eggs. If the top layer of your potting soil is always wet, it creates the perfect conditions for them to thrive. Let the soil dry out at least one to two inches deep before watering again. Most houseplants actually prefer this, and it can help prevent root rot too. Keeping soil on the drier side helps break the gnats' life cycle.
Use Bottom Watering
When you do water your plants, consider bottom watering instead. Set your pot in a tray of water and let the soil soak it up from the bottom. This gives roots the moisture they need without wetting the top layer. Over time, this method makes the surface (and your plant overall) less attractive to adult gnats looking for a place to lay eggs.
Add a Layer of Sand
Try covering the top of your potting soil with a half-inch layer of coarse sand. It creates a dry, rough barrier that fungus gnats can't easily move through. They tend to avoid laying eggs in it, and it also dries faster than regular soil. Make sure the sand doesn’t get mixed into the soil though, or it won’t work as well. Keep it as a clean layer on top to block access to the dirt below.
Swap to Gnat-Resistant Soil
Some potting soils hold too much moisture or have high organic content that fungus gnats love. Consider switching to a mix that drains faster and contains fewer ingredients like peat moss or compost. Look for cactus or succulent mixes, or make your own with perlite, coconut coir, and bark. Fast-drying soil helps limit the moisture gnats rely on to breed and develop.
Try Sticky Traps
Yellow sticky traps are an easy and chemical-free way to catch adult gnats. Place them close to the soil surface or hang them nearby. The bright color draws the gnats in, and they get stuck before they can lay more eggs. These traps also help monitor how serious the problem is and can cut down the adult population over time. Just replace them when they start to fill up with bugs.
Use Nematodes
These microscopic roundworms naturally feed on fungus gnat larvae in the soil. They're harmless to people, pets, and plants but deadly to the pests you’re trying to remove. Mix them into water and apply them to the soil. Once there, they start to work right away. This is especially useful if you have a larger infestation and want something more targeted without using harsh chemicals.
Natural Sprays
If you want to kill larvae and deter adults without hurting your plants, try using a mix of neem oil and water. Neem oil disrupts the life cycle of gnats and other pests. Spray the surface of the soil and the leaves, especially if you see adult gnats flying around. Do this every few days for a couple of weeks. Neem doesn't work overnight, but it helps over time and is one of the most classic treatments for houseplant pests.
Repot When Needed
Sometimes the best way to fix the situation is to give your plant entirely fresh soil. If the infestation is really bad, remove the plant from its pot, gently shake off as much old soil as possible, and replace it with clean, dry, gnat-resistant soil. Wash the pot thoroughly before reusing it too. This stops the cycle immediately and gives your plant a healthier start. Only repot if necessary, though, as it can be stressful for some plants.
Fungus gnats aren't dangerous, but they are persistent, and it usually takes more than one method to fully get rid of them. A combination of drying out the soil, blocking access, and killing off larvae will work best. Keep an eye on your plants and the soil, especially during wetter seasons or if you’ve recently brought home new plants. Catching this infestation early will help stop it from being a major annoyance later.