Spraying for gnats in the garden

What are Beneficial Nematodes?

Let’s start with how to pronounce “nematode.” Is it Neema-toad or neh-ma-tode? Well, according to dictionary.com, it’s….
What is a nematode? They are tiny, non segmented, cylindrical worms. They live in large numbers in places like water and soil. There are beneficial nematodes that help your garden, but there are also nematodes that can destroy it (roundworms).
If you don’t have the right mix of  microorganisms in your garden currently, beneficial nematodes might help your garden like I hope that it helps mine.
I mentioned in the blog post about the Garden of Eden Gardening Method, that I was getting a large number of fungus gnats around the new beds. Apparently, they are really attracted to the wood chips. It’s a great place for them lay their larvae.
The gnats aren’t harmful, just annoying, but their larva are a problem for gardens. The larvae eat plant roots and can kill young plants from the soil up. It’s hard to control the gnats in the air. I even tried putting out a bright neon paper with glue on it to try to catch the gnats, it didn’t work. I also put a few pieces of raw potato in the soil as the gnats supposedly like potatoes and will lay their larva there, and then you can dispose of the potato. That didn’t work either, they just love the wood chips.
So I ordered some nematodes on Amazon (these kind):
…to help combat the gnats. It wasn’t too expensive for the pack. And one package of nematodes should take care of my whole garden (about 100 sq. feet).
The nematodes are supposed to go after a number of unwanted species of insects that can live in your garden, including fungus gnats. In the package from Amazon, there was a cold pack to keep the nematodes cold. Then, to keep the nematodes alive, you are supposed to store them in the refrigerator upon receiving. Here’s what it looks like – a white powdery substance:
The Sf means Steinernema feltiae, which is the type of nematodes in the package.
The instructions stated to mix the package of nematodes with 1-5 gallons of water and then spray it on the garden. I mixed the pack of nematodes in a cleaned out milk gallon jug.
I then used a hose sprayer container like this one and turned the dial all the way up. If your sprayer has a tight filter, be sure to remove it so that the insects don’t get stuck inside and clog it up.
Spraying nematodes through hose sprayer
My spray container did not hold a full gallon of water, so I just filled it up a few times with the milk jug of nematodes, and sprayed it on all of my garden areas.
The nematode pack instructions say to keep the soil wet for two weeks after application. I’m crossing my fingers that this helps with the gnats. But if you read the reviews on the nematodes on Amazon, there were a number of people that didn’t even mention gnats, but said that their gardens looked better than ever after using these. I have high hopes! And I’ll update you all here on the blog.


It’s 2/12/2020, this post was initially written on 4/2/2019.

The gnats did go away about a month after I sprayed with the nematodes. However, it also got warmer at that point and the soil and wood chips dried out a lot (it was a wet spring).

In the fall, the gnats came back :(. I’m not entirely sure if the gnats larva couldn’t survive in the dry and hot conditions, or if the nematodes were active and did their job. When they came back in the fall, did they just re-multiply more than the nematodes could handle? Or did just get cooler?

I also added a large amount of wood chips again in the fall, and perhaps they are coming in on the chips. Or at least are just really attracted to wood chips. I won’t need wood chips for another couple of years, so I’ll update this post again later.

I also wanted to mention that I learned later that the soil temps do need to be warmer than freezing for the nematodes to survive, so it is best to apply them in the Spring when the temperature has warmed.

***End of Update***


As always, let me know if you have any comments or questions below. 

Happy Gardening!

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  1. Will this work for container/box gardening as well as larger, in ground gardens? I’ve never heard of nematodes, so thanks for sharing!

    1. Yup! I sprayed them on both my raised beds and in ground beds. You can actually apply nematodes to container plants in your house to combat fungus gnats. So, they help at any size.

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