Fungus gnats in the garden

Fungus gnats illustration

In late Spring Scott and I noticed the soil in the raised beds was crawling with little black flies. And not just a few, there were thousands. I have a quick scoot round the garden almost every day and didn’t see a hint of this problem the day before. It’s like they all hatched and crawled up to the surface at the same time. Feeling itchy? Me too!

We identified them as Sciarid Flies (fungus gnats). We’re still not completely sure where they came from but they like damp conditions and we’d recently had lots of rain and heavily leaky guttering from next door draining into our raised beds. 90% of the advice I found online was related to indoor plants, the prime cause being overwatering. But if your fungus gnats are in the garden the problem is much harder to tackle due to uncontrollable factors like rainfall. So I decided to write a post about controlling fungus gnats in the garden.

We wanted to try and tackle these flies naturally. We garden organically and don’t use any pesticides or insecticides. Here’s what we tried and how well it worked.

1. Vinegar traps

After reading lots of success stories about these traps it seemed worth a shot. I filled a container with vinegar, dropped a piece of banana in, made and funnel at the top and waited. In 2 days we caught 3 flies. And given how many there were, that was pretty poor. During the 2 days I was waiting for these traps to perform a miracle, even more flies surfaced. Which brings me to solution 2.

2. Yellow paper with Vaseline

I read about this online. It was a total waste of time because the little buggers walked off the Vaseline.

3. Bug spray

A few days later we declared an infestation. I bought some ‘natural’ bug spray containing Pyrethrumin – suppose to kill the flies. I sprayed it over the raised beds and the next day noticed it said not to use it near bees. I felt awful 🙁 Not only had I potentially harmed bees but it didn’t do a thing (our bee area is in the front garden so hopefully it didn’t get contaminated). I later realised this spray was a waste of time because it wasn’t going to kill the larvae anyway. Fail.

4. Flypaper

Fly paper brands

Magical, magical flypaper. A little sadistic but it worked a treat. The papers we used were chemical free, insecticide free and non-toxic. We put quite a few out and within 24 hours they were all full. I think this photo shows you the extent of our problem.

Fly paper covered in fungus gnats

Flypaper after 24 hours

We noticed a definite reduction in numbers after using fly paper. Success! All the flypapers were good in their own right. The Zero paper was good value for money and perfect for putting around the edges of the raised beds but I got glue all over my fingers every time I opened one. The Neudorff were easy to use and good for poking into the soil and The Buzz trap could be moved around the raised beds easily.

5. Gnat off

Reducing the number of flying gnats was all well and good but we needed to stop the larvae turning into flies too. We chose Fungus Gnat Off – a soil drench made from natural extracts suitable for use in organic gardening.

Fungus Gnat Off soil drench

I applied one soil drench and that was enough to stop things getting worse (stopped larvae developing into adult flies) and the remaining adult flies gradually died off or got stuck to the fly paper. It’s a little pricey at £22 for 250ml but it works and is one of the few products to specifically target fungus gnats. Worth every penny.

6. Soil drying

Hand cultivator in raised bed

The gnats don’t like dry soil so I’ve been using a hand cultivator to rake over the top couple of inches in order to dry it out. Its worked really well and the gnats moved away from the dry areas very quickly.

Good news!

The good news is that we no longer have fungus gnats in the garden and haven’t seen any in weeks. They didn’t get into the house and mummify us in our sleep. We lost a few younger plants but luckily everything else was okay.

Humans 1 – flies 0.

Do you have any methods that have worked well for treating this problem in your own garden?


  1. Don’t forget to warn users of the sticky paper the hazards to small birds. I do love your blogs Gemma they make me giggle 🙂

    • That’s good thinking! Those tapes are very sticky. Glad I give you some giggles 🙂

  2. Thank You for the help. I’m going to the store now! The nasty gnats are taking over my lil garden bed outside.

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