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Gnats in potting soil

Posted by 1dahlia4me 7A (My Page) on
Sat, Jun 18, 11 at 8:15

I moved 5 vegetable plants to larger pots yesterday, and used a mix of a couple kinds of potting soil, some leaf compost and a little vermiculite. One of the bags of potting soil must have been old -- had a bunch of gnats flying around as I did this. Now I'm worried that these gnats or their larvae are going to harm my plants. Is this something to worry about? What can I do to get rid of them? These pots are outside, so I'm not worried about the gnats themselves -- just what if any damage they can do to my plants. Thanks!

Follow-Up Postings:

RE: Gnats in potting soil

Read the other thread from this week called Fungus flies.. Neem EM..? They are almost certainly fungus gnats.

RE: Gnats in potting soil

Fungus gnats live in soil with leaf mold as you describe yours, and the larvae do eat the roots of your plants. A drench of BT is effective on the larvae. BT is available either in granules or mosquito dunks, and needs to be dissolved in Irrigation water. Al

RE: Gnats in potting soil

Yes, I did read that other thread after posting this. I'll drench with BT, thanks. I think I have some in the shed under the name of Green Step that I bought for tomato hornworm a year or two ago. It's meant to be diluted and then sprayed on the plant. Anyone know if that would work for this purpose?

I assume irrigation water just means the water I will drench the pots with?

RE: Gnats in potting soil

Green step is the wrong kind of BT. You want the kind for mosquitos and fly larva. The same people who sell Green Step also sell knock out gnats, which is the right kind of BT. Or you could dissolve mosquito dunks in the water you use to water the plants.

Thank you!

Thanks so much for the help! I'll go and get the right stuff.

RE: Gnats in potting soil

quick question, i was wondering if anything kills the bacteria? for instance i was going to drench my pots per the mosquito dunks instructions, but can i also add ferts/vinegar to it as well? or should i just treat the soil and wait to fertilize them?


RE: Gnats in potting soil

You can use hydrogen peroxide mixed with water ,I believe 10-25 % peroxide to water and put in a hand sprayer ,repeat every couple days till they are gone (3-4 times)
(The solution kills the adults ..not the eggs )
And is safe in the soil

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