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Gnats in Potting Soil

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Suddenly have an insect infestation after using potting soils? Tiny little gnats flying out of the soil in pots and your garden? Yeah, me too. I found out that they’re called fungus gnats, and they are certainly annoying!

flower pot with flowers and gardening tools against white backgroundI was so ecstatic to have put together my first raised bed for a vegetable garden. It’s nearly full with mushroom compost received from a neighbor, who got a huge haul at a local mushroom farm. The final touch was to add some garden soil to the top of the bed and plant some seeds.

Tiny Fungus Gnats in New Potting Soil

A special sale at a major home improvement store meant that organic Miracle-Gro soil was just $5 a bag – a pretty good deal. I got two and immediately added it to my bed.

(While this is my experience with this brand, I also tried EcoScraps potting soil and had the same fungus gnat problem. And plenty other people – see the many comments below – have also had issues with other brands, too.)

The next day, I went out to check on my raised bed and noticed the soil teeming with tiny little flies with white wings.

These insects were NOT in the compost before I added I the soil, yet appeared in droves within 24 hours of dumping the bag of soil into my raised bed.

I checked the mound of mushroom compost that I still had in another garden bed that was delivered the same day. Nope, the insects weren’t in there. I asked my neighbor if he had any problems with the tiny flies in his piles of compost. It was the same compost from the same delivery. That was a negative, too.

So I determined that the organic soil that I bought to complete my vegetable garden actually caused a HUGE problem that now I have to deal with.

Miracle Gro Organic Soil Gnat Infestation

Potting Soil Killing Plants

I bought Miracle-Gro soil (the conventional kind) last year. I had three healthy houseplants that I had bought from the store and kept in pots for a few weeks that were fine. When I decided to finally repot them I bought one bag of soil. All three plants were planted in this same soil, and then placed indoors and outdoors in different locations.

ALL of the plants started developing problems and were infested with gnats. I lost $30 of plants, tons of time in taking care of them, and time spent to return the stuff to Home Depot where the cashier looked at me dubiously as to how my soil could have caused this.

Problems with Fungus Gnats and Potting Soil

Now, fast forward another year, and I’m researching gnat insect infestations online (I have SO much time in my life to do this, by the way) and finding out that this is a very common problem with bagged soils, as evidenced in this stream of negative reviews.

This is such an issue that the first comment for these gnat bait traps on Amazon speaks directly about using the baits to kill gnats on houseplants brought in due to bagged potting soil. Apparently these will work, but I haven’t tried them out.

The solution in review comments is that there is a money back guarantee. How do I put soil back into a bag ripped in half in order to get the soil out? How do I return this nasty stuff to the store without getting it everywhere all over my car?!? Most importantly, what about MY time??? The time spent in researching this problem, in tending to plants at risk, to monitoring insect populations and in applying remedies? Isn’t my time more valuable than the $5 that I spent on the soil??

Check out my course on easy to grow, hard to kill houseplants to add to your home right now! These gorgeous plants will start detoxing your indoor air immediately:

Best Houseplants to Detox Your Home

house plant in pink pot close up

How to Kill Fungus Gnats

Responses to fungus gnat infestation complaints generally say that the gnats are not a problem to humans. And they cause little damage to plants.

The University of California Integrated Pest Management says differently. They state that a large infestation can kill seedlings or young plants.

The company’s response is also that adding 1/2 inch or more of sand to the top of your pots will help control the fungus gnats.

Which is good news for those of you who were wanting the look of houseplants planted at the beach or love the feel of the Sahara desert in your garden bed.

P.S. If you don’t mind the look of sand or rocks on your houseplants, here’s a recipe for how to get rid of fungus gnats using sand.

Also great for those of you who want to spend more money on unnecessary products when all you really wanted was a simple bag of potting soil and to be done.

But hey, now you get to go back to a garden center and buy sand and plant sprays and plant amendments. YAY!!!!!!

I had tried soaking my garden bed with insecticidal soap, which apparently doesn’t work on killing fungus gnats.

Adding sand to my garden beds was not an option for me. I was not going to buy a bag of sand, nor did I want to mess with this issue any more.

I basically just lost the entire garden bed and never went back to try again.

Related Posts:

Potting Plants in Compost

After this experience, I don’t buy potting soil at all anymore.

I use straight mushroom compost to pot my plants. I buy mine at Lowe’s, where the price is comparable to a bag of potting soil, but you can buy mushroom compost online here).

Everyone says never to plant your plants directly in compost. Maybe that’s for rich compost straight from the backyard. Or only cow compost. I don’t know. But what I do know is that I’ve never had problems planting any plant in mushroom compost or worm casings. It costs a little more, but I don’t have to buy soil amendments, fertilizers, insect sprays from bringing in gnats in potting soil, etc.

If you don’t want to avoid potting soil and use compost, then I suggest you don’t try to pinch pennies like I was. Go to your local garden center and get your potting soil from them.

 

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Rebecca Cullen

Saturday 30th of April 2022

I had the same creepy problem, but as long as I use the mosquito bits and yellow sticky traps it keeps them to just a few. I got lazy the past few times I watered, and they started back again. I will say it did take time but I had only a couple once in a while, as long as I continue with the bits. Thanks for advise on Miracle Grow...what a loss for so many of us gardeners. Now, if I could get my Indian Rope Hoya to bloom, I'd be happy.

Dawn

Sunday 30th of January 2022

NOT FISH LIQUID SORRY THAT IS DISH LIQUID A NATURAL ONE. SPELL CHECK IS MY NEMESIS

Dawn

Sunday 30th of January 2022

I had big problems with fungus knats from any potting soil i used. My house my swarming with them flying in my face ahh so annoying. Here is what i did to get rid of them. I bought mosquito bites soaked them overnight and watered my plants with it. I used neem oil mixed with fish liquid ( very little) i rubbed it on all my leafs under and over EVERY LEAF i bought the yellow sticky thing and put one in every pot and hung them above the plants. I also bought a small bug light and leave it on and hear that light just snapping them bugs. Its a battle. Be vigilant. It took me a whole year to be pest free and i put any new soil in the microwave or i let it dty in the sun and coat it with pesticide. So ALL POTTING SOIL IS INFECTED WITH BUGS.

Jay

Friday 1st of October 2021

I have gardened for 50 years and my fungus gnat problem started this year. 6 different potting soils infested. Please everyone, start Sending complaints to the USDA so this problem gets fixed. We should not have to lose plant or spend additional money to solve this problem that is caused by companies cutting corners by not treating soil correctly

Sheryl

Sunday 9th of May 2021

I have always had large beautiful house plants. I didn't even know house plant gnats existed... until i bought a large bag of Miracle Gro. What a NIGHTMARE. I had gnats everywhere. I called Miracle Grow customer service, no help. I called the upper Management. They told me to pay for a plant specialist to come out & help me!! The gnats were so bad, i lost several plants. In addition, the cost to find a way to get rid of these really added up. Miracle Gro did not give me a refund. I will NEVER buy any of their products again. I wouldn't even allow their products in my house, if they paid me. Really disappointed in this company. I wouldn't buy anything that was sitting close to Miracle Grow!!