Gnats in Potting Soil
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!
I 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 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 another organic brand of 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.
Potting Soil Killing Plants
I bought the conventional kind of soil from the same brand 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 and finding out that this is a very common problem with bagged soils.
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.
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 ½ 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.
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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.
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.
Sterilize the soil you are going to use by putting it in a hot oven for a few minutes. Simple. Will give your home a nice earthy smell too. Don’t leave it in too long though. And take it out of the bag first for God sake!
Thanks for the note to take it out of the bag! Could you imagine that melted plastic mess otherwise?!? Yuck!
It’s not just Miracle Gro. It’s any potting mix that has ground wood mixed in. I’m DONE with commercial mixes. Everyone says it’s over watering that causes them. Phooey! I’ve raised house plants for YEARS and never had this problem until they began adding ground up wood. It’s a cheap filler so they can make more $$ pr bag and they are all doing it. I’ve tried everything to get rid of them and always end up throwing my plants out. 1 female can lay over 200 eggs. It’s a losing battle. Say no to ground wood in potting mixes!
Terry, I’m going to agree with you on that. I’ve had so many problems with potting soils of all types, even organic ones. My answer is to use straight mushroom compost. When you are just trying to pot a pretty plant, though, it’s so cumbersome to try to find the perfect potting mix or other soil medium quickly. I feel like you have to plan out your entire gardening plan. And if you run out, then you end up having to go buy the bad stuff at the nearest retailer.
Though it wasn’t miracle grow (it was organic potting soil from home depot) I too found a seemingly uncontrollable fungus gnat problem. I tried everything I could find locally, traps, poison, apple cider vinegar, beer, hydrogen peroxide all with zero success. It took months. Then I ordered some Beneficial Nematodes (S.feltiae) off of the internet. The first package came in the heat of summer and they may have been dead (I didn’t have a microscope to examine) so I contacted the company on a cooler spell and got a new package sent out. Within a very short time no more fungus gnats. I probably had spent a year trying different solutions never really believing that the Beneficial Nematodes (S.feltiae) would work. Once again I was wrong. Now looking for the correct temperature to kill them from potting soil before I start some new plants I came across this article. Though I didn’t read through ALL of the comments I did not see anything about Beneficial Nematodes (S.feltiae) and figured it was my public duty to share my experience! Just another FYI there are supposedly different types of Beneficial Nematodes and from my research that is the “S.feltiae” I didn’t try any of the other types so I would stick with these.
Kevin, Thanks for the great tip! No, I don’t think anyone has discussed nematodes as an answer before. We all really appreciate you helping us out! It seems that it could potentially be a problem with any type of brand, so thank you for the heads up!
OMG my plants are doing good and now these bugs Micracle Grow was the best to buy. I came right in to look this up went to 3 sites before yours. Thanks for talking about Peroxide mixture I will try it tomorrow.I thought the mold was from using rain water from roof sometimes.
Hi Carol! Glad you found this site! I can’t believe that rain water would ever cause mold. It seems like it would be the purest water! Hope you find success!
I’m not sure when your post originated but, 2018 I’ve had the biggest mess with Miracle grow! Today I finally figure out it’s the potting mix. I cannot believe the amount of time & $$ I have wasted! . I’ve been on a viscous cycle. Gnat infestation. Figure out what kind, where coming from. I had them in my house during the winter! Id just bought my house so everything here is new to me. Plumbing issues? Sounded like drain gnats. Put out fruit traps. Bleach in drains etc. Then try this. Then this. More gray hair. Loose several plants…start fresh again and again and buy a few new plants to replace the ones that are almost dead. Of course, buy a couple new pots and try a new plant of some kind. In other words, when i go to Lowes or HD…Cha ching! And repeat. And repeat. I did not know what the eggs looked like until today! I didnt know the larvae I was seeing was gnats. And they have done more to my roots than a “little” damage! Just lost my largest sago this week! Its been hot since February it seems with high humidity and lots & lots of rain. I’m trying one more thing…mosquito bits. If that doesnt work I’m done! One gnat lays 200 eggs. I will never buy a miracle grow product again!!!
I’m exhausted! Hope you can decipher my rant!
Kimberly, Yikes! That sounds so expensive. And losing a sago has got to hurt! This post originated about 5-7 years ago. So sad you’re having the same problem.
I had this problem with miracle gro a few years back and thought perhaps it was just a bad batch. I decided to take a chance and purchased orchid bark and had no problem. I was convinced then that the issue must have been a one-time deal so I bought two bags of potting soil and repotted all of plants. All of them. Not only have I lost my house plants, but the orchids have been infested as well. I’m so disappointed that a company who puts itself out there as a name that people can trust can be so callous and cavalier about the damage they cause. Shame on you, Miracle-Gro. Shame on you!
Jennifer, I’m so much happier planting my plants in mushroom compost. It is so expensive to buy bad potting soil and then have the plants die!
I found a way to get rid of them. After drowning my soil with peroxide and Dawn and other remedies which didn’t help, I took tiny bottles and stuck the bottles in the soil away from plants and filled with apple cider vinegar. The gnats love the vinegar and drown. It took awhile but they are almost extinct in our house. One has to repeat the vinegar each week. I also placed a cup of vinegar under a light which is always on. I caught many this way.
Jackie, This is brilliant! Thanks for sharing this gnat killing tip! I hope others have great success, too!
I had the same problem with fungus gnats. I bought organic miracle grow potting soil for some new indoor plants. I researched the growing infestation and learned about fungus gnats. I spent money on pots, soil and plants, only to have to move everything outside, spend countless dollars on food safe pesticides for my herbs and cat grass. Miracle Grow Organic Potting soil…..now trying to figure out a way to decontaminate my soil…..high heat?
Rose, I totally understand! I don’t know if high heat would help. How would you get the soil a higher temperature than the ambient air? It’s frustrating, right?
The soil companies use to heat the indoor soil with high heat which made soil perfect for indoors. I guess miracle grow skips this step. I tried heating my own once and the fumes made me very ill. Not worth it to heat. Miracle grow is getting soil from landfills so it’s probably the most toxic soil on earth.
Being we don’t know what is in their landfill dirt, it’s not worth the health risk to heat it and get the fumes in your home.
Well – this has just happened to us too with the organic Mirical Grow soil. Hundreds of gnats swarming!!! I feel the same frustation as all of you do. I made a flower bed about 3 hours ago. I didn’t notice anything until i went out again to continue to work on the bed … then a swarm of these things hovered all around the bed. I had not planted my lantana yet so I shoveled up the soil, put it in my wheel barrel and sprayed it with bleach and wasp spray. I did however use a small portion of this soil to make 2 pots of seeded flowers. I have not checked those yet, i will check tomorrow. What a totally frustrating situation. I will probably put the infested soil in a big garbage bag and return it and the 2 opened bags of soil and get our money back. I’m worried that the gnats might have landed around the bed where I shoveled it all up….. . I will use the peroxide around the bed tomorrow. Ugh!!!!!
Ugh! How frustrating! I know the feeling! All of that work. And so many times the plants and seeds that you started can’t be easily replaced. I hope you find success in returning the soil and not having any more gnats swarming your garden.
It’s not just Miracle-Gro — it’s all brands of potting soil. They all get infested with fungus gnats. I am starting to wonder if the gnats have evolved to be a lot stronger and survive better….I never had problems with gnats back in the 80s and 90s. It’s only been the last decade or so that I just can’t get rid of them. I have even found that sterilizing the soil at the recommended temperature might not kill them. I have to turn the heat up to 300 for 90 minutes. I live in Arizona and maybe the gnats here have adapted to the hot temps. I don’t know. In the 80s and 90s I lived in NY and CA. I have only had gnat infestations in AZ. So, it’s either due to the conditions in AZ, or maybe it’s worldwide/countrywide in last decade or so. The gnats just seem invincible now.
I was about to throw out several beloved plants just now, but I am considering the peroxide solution and seeing if that works. I don’t know. I’m so fed up at this point. I already repotted all the plants with sterilized soil a few weeks ago (for the second time!), but I didn’t remove the old soil from the root ball because the plants are too big and wouldn’t be able to be anchored in the soil properly if I did that. I just replaced the loose soil from the 1st repotting. So, I don’t know if the gnats were in the root ball soil or if the sterilized soil still had viable gnats in it. Extremely frustrating.
I can’t use chemicals/pesticides because I’m chemically sensitive and I have pets.
Fingers crossed for the peroxide to work….
I’m finding the gnats in potting soils, too. I’ve just given up using potting soil and use straight compost instead. I use mushroom compost with no soil and find it works great!
i have the same problem with Miracle Gro in my raised garden. I tried hydrogen peroxide but it isn’t supposed to be used on zucchini and brussels sprouts. They yellowed and some leaves died. Does the sand work? I have an vegetable garden so I can’t use pesticides like the ones that are used on houseplants or outdoor plants. I sprayed with Earthtone organic insecticidal soap today to see if that works. Suggestions for organic vegetable garden?
Cathy, I use organic farming methods, too. I honestly don’t know the best solution. I didn’t try the sand because my plants were already dying. You might want to look at my post on how to get rid of gnats (search in the search bar to to top right on a desktop page or at the bottom on a mobile page). I simply had to start over, unfortunately. I like insecticidal soap the best out of all of the natural solutions that I tried.
So I started my garden with miracle gro soil and experienced the same thing. What a mess! did not realize it was the soil (my garden is on a balcony in containers), till about a month later I had to add more soil. Now, I had already done my research but did not see this about miracle gro because i did not suspect the soil..From my research I knew what the gnatt eggs looked like and had been picking them out relentlessly. So I poured the extra soil I needed to top off what I originally had planted my plants in and guess what…….eggs everywhere. And I know it was in the soil as i had it in a protected tub. I had to go through the plants I topped off and collect the eggs and it was at least 25-30 of them. They weren’t there before as I had just looked through them before i added the soil. I am furious. I trusted them and this has made my growing season just miserable
Kathleen,
That’s horrible! When you can specifically pinpoint the problem (as in a balcony container garden), it is so much easier to figure out what the problem was. Hoping you get some relief from all of those gnats!
I am also in the same boat but have a question… I had purchased the large bag from Costco… Thinking the miracle gro organic potting soil would help my plants. I repotted some herb plants for indoors and a bunch of herbs in window boxes and clay pots outdoors. I noticed my plants were not growing very well in either location and then saw the gnats indoors. I tried vinegar traps and raw potato but when it did not help I moved them outside and noticed some more gnats by the bag of soil and some by my basil plants in the same soil. The next morning there were hundreds of gnats… Soooo glad I moved it outside but I had to trash most of the plants. My question is can the fungus the gnats feed and breed off of also cause fusiliam wilt and kill my basil and parsley? The plants were gorgeous and healthy before repotting with the miracle grow soil. They stopped growing and then showed signs of the wilt. My other herbs and plants using the other raised bed mix or potting soil seemed to have faired better.
Michelle, Yikes! That sounds horrible! I don’t know about the fusiliam wilt. I do know that I, too, had perfectly healthy plants until I repotted them, then it was downhill from there. So who knows?