For at least the last 10 years we have started our seedlings and herbs inside instead of purchasing plants from a garden store. Over the years we've learned how to deal with a variety of issues and pests. The most annoying has to be the fungus gnat! Some years we only notice a few around the time we start hardening the seedlings off. Other years, like this one the gnats have been annoying enough to take action. I know many of you also start your seedlings indoors so I wanted to share with you how to get rid of fungus gnats in plants, organically! Each of these methods can be used for houseplants, seedlings, and even container plants outside.
What is a Fungus Gnat?
Fungus gnats are a grey-winged beast with a slender, black body and are commonly mistaken for fruit flies. Make no mistake, they are equally as annoying as fruit flies. The big difference is instead of taking up residence on your fruit they move in and take hold of your plant soil.
Fungus gnats don't usually harm well-established plants however, on occasion they will snack on the roots of your plants while they are searching for fungus.For those of us with seedlings, the gnats are especially worrisome because fungus gnats can also spread a pathogen that causes damping-off, a condition that kills seeds before they sprout and weakens or kills seedlings just after sprouting.
Fungus Gnat Life-Cycle
In order to cure an infestation, it's important to understand the lifecycle of the gnat. Understanding the life-cycle allows you to see why there isn't one quick and instant way to kill them. Dealing with the infestation will take time but once you do there are ways to prevent reinfestations or at least stop the cycle if you happen to bring them in on a new plant to soil.
How to Get Rid of Fungus Gnats in Plants, Organically!
You'll probably notice them immediately when you add water to your soil. They don't want to drown, so they all buzz to the surface and fly around your plants and/or face. It's incredibly annoying. They must be stopped!! Here's how:
- Let your soil dry. We know fungus grows in moist conditions. If your soil stays wet for over a week, move it to brighter, dryer conditions for a bit. Just don't completely forget about the plant. Sadly I lost two seedlings because I didn't notice the soil had dried out too much.
- Drown them out. This is what I have found to be the easiest way to do break the life-cycle of the gnats. Mix equal parts 3% hydrogen peroxide and water. This will kill larvae and eggs in the soil. This solution is gentle and will not harm the plants. This is best done once the plant has begun to dry out to avoid overwatering.
- Bacillus thuringiensis-Bt is a bacterium that occurs naturally in the soil. Bt var. israelensis (Bti) kills the larvae of fungus gnats. Follow the directions on your product to make a Bti drench and use it to saturate the soil in your potted plants. It will coat the plant roots without harming them and kill fungus gnat larvae that try to feed on them. You can find Bti formulated for houseplants and outdoor plants.
- Hang sticky traps. Adding sticky gnat traps in and around your pots will help catch the flying adult gnats. The gnats are drawn to the color yellow and when they land they become stuck to the sticky paper.
- Monitor daily. Inspect your plant frequently for any sign of survivors. As soon as you notice any signs of the fungus gnats repeat one or several of the above methods.
Now that we have the gnats eradicated or at least under control here are some steps you can take to prevent them from coming back.
- Inspect your plants- Anytime you receive or buy a new plant it's a good idea to inspect the plant and the soil it is in. Most shops and nurseries are vigilant about pest control, but it's not always possible to eliminate all pests. I skipped this step this year and I'm pretty sure the gnats I just had to deal with hitched a ride in on a new aloe vera plant I bought.
- Use pesticides- Neem oil is a natural pesticide that can be safely sprayed on plants to prevent pest infestations. Neem also has anti-bacterial and anti-fungal properties. Neem oil spray can control Powdery Mildew, Spider Mites, Russet Mites, Broad Mites, Botrytis, Grey Mold, Aphids, fungal and parasitic species on plants.
- Covering the soil-If you prefer a less direct approach to Fungus Gnat eradication, covering the soil with sand or rocks can also work. Simply cover the entire top of the soil in either a few centimeters of sand or small rocks. The sand prevents the newly-hatched adult Gnats from reaching the surface and breeding, and similarly, the rocks prevent adult Gnats from reaching the soil to lay eggs. This is not a method I have had much success with once the infestation has progressed but it's one a lot of people suggest so I'm including it.
- Avoid Soggy Soil- Let your houseplants or outdoor plants dry out slightly between waterings to discourage the adults from returning and laying more eggs.
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