Fungus gnats (probably) in bagged compost

SueAtoo · October 2023

I have a recently opened bag of MPC in the garage which has loads of little flies which I assume are fungus gnats flying around. Should I dispose of it or will the grubs die off over winter if it's cold enough? I've used nematodes previously on my indoor plants.

Fire · October 2023

Are the gnats a problem in the garage? Getting into the house? If the compost is being used outside in future, I don't imagine they would be a problem. If the MPC is being used inside, forum people have recommended in the past: putting small batches of compost in the oven on a low setting for a while; or boiling and draining it; feeezing it or microwaving small batches for houseplants. Mosquito dunks/bits are also an option to treat the compost - a little goes a very long way.

Personally I put up with the gnats in the house, as plants are constantly coming in and out. I use a small handheld vacuum to hoover them up when I get irritated with them.

Dovefromabove · October 2023

I’ve rarely opened a bag of compost that didn’t have some gnats. I s’pose the fact that I open it outside is the reason I don’t worry about it. I do start some seeds etc off indoors and occasionally see some gnats inside but they usually disappear in a few days.

We have got a load of fruit flies in the house at the moment … now they really are annoying, and I can’t track down where they’re coming from … 😖

GardenerSuze · October 2023

I think it is more of a problem if the compost is wet.

Fungus gnats (probably) in bagged compost

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