Admittedly, I had never battled fungus gnats until now. In my opinion, our current problem is the result of quite a few issues. First, we had a very wet winter. Even with our irrigation shut off, the soil stayed wet for days at a time. Also, for the first time we started to incorporate a lot more fabric pots and containers into our garden (mostly because of seedling overflow). Houseplants, containers, and anything with light and fluffy soil mixes are prime territory for fungus gnat larvae to settle in. I’ve noticed that the potting mixes contain a lot of aeration material that makes a great home for these little buggers—light, fluffy, with some wood chips. Also, we freshly mulched our front yard garden during this cooler weather and the moist mulch created a wonderful home for gnats. Yuck!

Why do we not like fungus gnats?

First off, they are annoying. As I bent down to harvest some kale from the front yard garden, these tiny little gnats flew all over. It’s annoying, gross, and it doesn’t look clean to passerby. More importantly, under the soil these gnats can transmit fungus to the roots of your plants and start eating those infected roots. Your plants can start yellowing, dying, and stop growing altogether. Fungus gnats eat fungal growths in the soil which means that, as they work their way from plant to plant, they can easily transmit fungal diseases.

I should specify, we are mostly concerned about the larval stage of the fungus gnats. They are the major transmitters of disease and do the most root damage. The adults don’t cause damage, although they are the most annoying part. Once the adults lay eggs, it can take 4-6 days for those eggs to hatch into the larvae. It’s the larvae that are the main culprits of damage in the garden, and they can wreak havoc on your plants for almost 2 weeks.

Disclaimer: there are different varieties of fungus gnats. I highly recommend researching pictures of fungus gnats native to your area for accurate identification.

Treatment Options↓

Manual Removal

This option should be tried first. Why? Well we always want to try the gentle methods first before adding anything to our gardens.

Simply scoop off the first two inches of soil (put in trash NOT compost) and replace.

Let your soil dry out between waterings to prevent further infestations.

Sticky Traps

For those annoying adult gnats, try these sticky traps and see what you can catch. The more you catch, the less egg laying will occur. Watch vigilantly and see if you notice lower numbers over the course of a week.

NOTE: I was having problems with fungus gnats in my grow bags recently, I simply placed a couple of these sticky traps around the bags and caught so much! I even learned that these traps will also catch those pesky leafhoppers that can leave light colored speckles all over your leaves. That is leafhopper damage.

Hydrogen Peroxide Drench

Sam and I did a hydrogen peroxide drench in our front yard garden (twice) and have seen significantly less fungus gnats. The key here is timing and making sure you let the soil dry out in between treatments. Also, dilute, dilute, DILUTE!!!

Warning: hydrogen peroxide is made up of oxygen and water. If you use too high of a concentration, or too much, you can kill your plants. It’s the same idea for any kind of fertilizer or treatment—using too much of anything can be harmful to plants. Over time, hydrogen peroxide will break down into oxygen and water, making it extremely safe to use in your garden and organic.

Hydrogen peroxide comes in different levels of potency. For this treatment, use a 3% hydrogen peroxide (you can find this listed on the bottle). From there, we will dilute this even more with water. 

This is the hydrogen peroxide I used. Make sure it is 3 percent, topical.

Process

Mix one part hydrogen peroxide with four parts water.

Water around the bases of your plants. The peroxide should kill the larvae on contact.

Do this at dusk so it can absorb and kill overnight.

Do not water your garden after this treatment, and let the soil dry out afterwards. This will ensure the larvae are dead and make the soil less hospitable to adults wanting to lay eggs.

You can repeat this process again after approximately 5 days. That gives any eggs in the ground time to hatch so they can be killed in the larval stage, and whatever adults that are currently alive will have ended their life cycle. Depending on the severity of your infestation, you may need to repeat another drench in another five days.

So that concludes our battle against fungus gnats in the garden. We were very pleased with the results, and might do this drench one more time to really extinguish them. Also, I have been more conservative with my watering in hopes of cracking down on these pests. If you haven’t read my other articles in this organic pest control series, I encourage you to see below. In general, letting your soil dry out in between waterings will actually help deter a multitude of pests because many of them like moist environments.

The Organic Pest Control Series

For the past month I have been performing experiments and sharing what has worked for us in the battle against pests in the garden. I prefer a generally hands-off approach because I believe gardens are a balance of “good bugs” and “bad bugs.” Patience + responsible management is the way to go. We have been employing this philosophy in our own garden from the very beginning and I can see big, beautiful changes over the years as our habitat evolves. To learn more about what it means to garden organically, see the Instagram post below: