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Gnats or flies in soil

Posted by mwolfson (My Page) on
Sun, Nov 12, 06 at 16:48

I am getting little gnats or they may be small fruit flies developing in the soil of some of my houseplants. Any suggestions on how to get rid of them and prevent them?

Follow-Up Postings:

RE: Gnats or flies in soil

They are most likely fungus gnats.
Allow the soil to dry out completely for 24 hours before watering again.
The larvae can't survive in thoroughly dry soil, but the plant will.

RE: Gnats or flies in soil

1.) Increase air circulation around the plant 2.) allow the soil to dry more 3.) use yellow sticky traps to capture the adults 4.) if plant has tons of larvae- you can also stick a couple pieces of raw piece of potato in the soil to attract and kill them. Another choice for abolishing the larvae is to place diochatemous(sp?) eart on top of the soil. The sharp pieces cut up the little maggoty bodies. BUT, DE should not be sprinkled without a mask covering your nose. It poses a potential hazard if not used properly.

RE: Gnats or flies in soil

Gh, what is diochatermous? LOL And how does a potato help? That's a new one. If my plants ever get gnats, I'll have to remember your home rededy. Where did you hear about the potato?
If DE shouldn't be used w/o wearing a mask, I'd apply it outside, depsite the cold. Toni

RE: Gnats or flies in soil

I wouldn't use DE if you have pets, either.

Drying the soil is the easiest way to go. Fungus gnats should not kill a healthy plant...the larvae eat new roots, usually those of seedlings.

RE: Gnats or flies in soil

Below I'll like to the wiki on DE.

On top of allowing the soil to dry if you can find some carnivorous plants like bladderwarts to help keep the pests down without the use of chemicals or DE.

Here is a link that might be useful: DE

RE: Gnats or flies in soil

R- thanks for providing that informative link to DE.

Toni- I'll provide a link for the potato slices. There's ton of info out there on it and has also been discussed last year on this forum.

Happy reading everyone!

Here is a link that might be useful: One Potato, Two Potato

RE: Gnats or flies in soil

DIATOMACEOUS EARTH is safe to use around animals as long as they, too , are not allowed to INHALE it while it's being applied. DE (horticultural grade/food grade...NOT pool filter grade) can be fed to animals (and people), used as a dust, etc. It just must not be inhaled. You can find DE in any decent garden department or garden center. Once applied to the surface of the containers, it's perfectly safe. BTW, we all ingest DE practically every single day. If you eat any grain or seed product (flour, cereal, peanut butter, rice, beans, pasta, bread, etc.), DE is a part of your daily intake. It is also in pet food, bird seed, etc.

You should consider changing your potting medium to one which cannot support fungus gnats, as well as monitor your watering regime. I (personally) opt for a very coarse textured potting medium and have not seen a fungus gnat for many years.

But let's not forget the tried and true fungus gnat larvacide, Gnatrol. The same active ingredient is also found in mosquito dunks, Bacillus thuringiensis-i. Following the directions on the product, you water it in on your normal watering cycle. After a few applications, all of the larvae are well as the adults, which live for only a few days.

I think I figured out the best solution.

Go to the beach, or go to Home Depot and buy some sand. Take a cup or scoop and spread a layer of 1/2" to 1" of the sand over the top of the soil in your potted plants. The sand serves as a barrier that traps existing gnats and larvae underneath. It kills them all. It also serves as a barrier to keep the gnats out as well.

I've dealt with this problem on multiple occasions. I think every damn bag of soil must be infested with the gnats or larvae, because it seems that every time I buy a bag of soil and pot my plants, over the course of the next few weeks my home ends up infested with gnats.

This solution, of course, will change the look of your plants. But, it's kind of a nice look. It's clean and if you put a few shells and rocks in the sand, it's kind of a nice designer look. I've included a link to a photo I took. I just did this yesterday after getting fed up with all the gnats.

Works like a charm. You will notice, after putting this layer of sand on the soil, that over the course of the next week or so, the gnats will be gone.

Believe me. This works. Every plant in my house has a layer of sand spread on the top of the soil. Any time I have done it, the gnats were gone shortly afterward.

Here is a link that might be useful: Photo of Sand in Potted Plant

RE: Gnats or flies in soil

I have a question for johnyblaze about the sand, how does this effect the watering? Wouldn't it just turn muddy and still attract the gnats or would it not because the sand wouldn't produce fungus?

Also, I have read on a few sites and magazines that using dish liquid and vinegar will attract and kill the gnats but it hasn't worked for me yet. I have tried the past 2 months to get rid of them. Also my plants are growing a lot of the fungus on top of the soil. I have grown up with house plants and have never had this problem until this year. Is it the soil I am buying, the plant food I use, the town I moved to, the water, the old home I now live in? When I planted new seeds in the spring I used the starter mix and the organic pots and went by my normal routine, fungus had grown so rapidly in them that none of the 60 survived!! Some of them grew very skinny up to about an inch then died! The fungus had completely taken over the pots!!! I have never had this problem in the 20 years although it has been about 5 since I have grown....the differences were the town, house, city water, and the soil. before I just used the soil from outside or regular dirt and no fungus grew....and no gnats!!!


RE: Gnats or flies in soil

I think they have new and improved the soil to the point that its worthless. I purchased a bag of miracle Grow potting soil as Ive been for 20 years and its like a dark brown saw dust... after repotting several plants I went to water them and the potting soil floated right out of the pots..I also have a problem with the gnats now too.. I know the Miracle grow I had been buying for years was dark in color almost black with the white balls in it.. what happened to that .. It was the best.. why do they keep fixing things that aren't broken..

RE: Gnats or flies in soil

I've only had problems with these when I used potting soils with lots of peat or vermiculite.

Repotting is the easiest way to get rid of them immediately. Remove plant from pot, throw the dirt in the garden and replace with new. Rinse roots. Avoid them in the future by letting the soil spend more time dry. If you put compost in pots, let it bake in the sun until completely dry and crispy before using it, bagged or homemade.

tinaham, I totally agree! But have always hated having the perlite (white balls) since they look so unnatural and tend to "float" to the top. I also don't like to waste space in the container on non-organic filler.

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