Forum home› Problem solving
This Forum will close on Wednesday 27 March, 2024. Please refer to the announcement on the Discussions page for further detail.

Sterilising potting soil at home (fungus gnats - argh!!!)

Mr. Vine EyeMr. Vine Eye Posts: 2,394
in Problem solving
Morning all, this year we’ve had a major problem with fungus gnats in the house - they started from the chilli plants we had growing inside, and then spread to every other plant in the house. Had never had this problem before.

Had sticky traps everywhere, peroxide washes of the soil and regular clapping of them out of the air 👏🏻 

Finally got on top of them. But they’re starting to surface again now - from a new plant that I’ve grown from a cutting.

They must have originated from the same bags of compost I used last year. Curse you cheapo Aldi bags!! Curse youuuu!!!

So I’m thinking that this year I only want to be using sterilised soil for house plants/seedlings/cuttings growing on indoors, just to try and reduce the risk of it getting so bad again and introducing new pests into the house.

Has anyone done this? I know one option is to oven bake the soil - this would obviously cause a stink, just wondering how quickly it dissipates. Any experience from people who’ve successfully done it.

thanks


East Yorkshire
«1

Posts

  • FireFire Posts: 19,096
    Last year was terrible for fungus gnats in my house - infestations - and I have never had this before. Baking the soil before use is an interesting idea.
  • Mr. Vine EyeMr. Vine Eye Posts: 2,394
    @Fire - just read online that you could steam it, sun sterilise it but that’s obviously going to be patchy, or oven bake in trays covered with foil on a lowish temperature (100ish)

    But I don’t want to cause a massive stink that doesn’t shift from the oven!
    East Yorkshire
  • purplerallimpurplerallim Posts: 5,287
    Would pouring boiling water over a tray of compost work? It could be left until cold then drained ( would be a laborious job, and I suppose the water could be kept so nutrients weren't lost🤔) I too have them in the house after potting up coleus cuttings
  • Jenny_AsterJenny_Aster Posts: 945
    How about using a bbq to steam the compost? 
    Trying to be the person my dog thinks I am! 

    Cambridgeshire/Norfolk border.
  • Pete.8Pete.8 Posts: 11,340
    I don't think it will make any difference if you sterilize the compost.
    If the compost is suitable for them to lay eggs, they will sniff it out and appear as if from nowhere.
    Even at this time of year I can see plenty of them in my compost bins.

    I've found the best way of keeping them away is to put a layer of gravel on top of the compost in the pot.


    Billericay - Essex

    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • REMF33REMF33 Posts: 731
    I noticed I have them on my seedlings in the greenhouse. I am new to greenhousing. Will this be a problem? (Beyond being irritating.) Does putting gravel on things retrospectively help? (Can't really do it with the seedlings though as they are autumn sown and very small.)
  • thevictorianthevictorian Posts: 1,279
    I don't think sterilising the soil will work out longterm either as they will just make their way into the soil later. There are things like sb invigorator that you can spray onto the soil and plants (you need to repeat it to keep on top of them) or other products (I think mosquito pellets) which reduce the numbers but because they move about like aphids it's hard to eliminate them. I have some but find that don't do much damage and by keeping the soil less wet they are much reduced.
  • Pete.8Pete.8 Posts: 11,340
    REMF33 said:
    I noticed I have them on my seedlings in the greenhouse. I am new to greenhousing. Will this be a problem? (Beyond being irritating.) Does putting gravel on things retrospectively help? (Can't really do it with the seedlings though as they are autumn sown and very small.)
    I don't sow anything until late Feb, but I also see plenty of them around my seed trays in the propagator. They don't seem to cause any problems as the seedlings grow quite fast.
    There's some advice here from the RHS - 
    https://www.rhs.org.uk/biodiversity/fungus-gnats

    Billericay - Essex

    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • Pete.8Pete.8 Posts: 11,340
    thevictorianzFH0qqPW said:
    I don't think sterilising the soil will work out longterm either as they will just make their way into the soil later. There are things like sb invigorator that you can spray onto the soil and plants (you need to repeat it to keep on top of them) or other products (I think mosquito pellets) which reduce the numbers but because they move about like aphids it's hard to eliminate them. I have some but find that don't do much damage and by keeping the soil less wet they are much reduced.
    SB Invigorator does work from what I have read. It's not something I've used though.
    It's basically Neem Oil and works by covering the insect in an oily film (that is harmless to plants) and the insect dies, but it does have to be used regularly to be effective. I just don't like the idea of spraying oil onto plants and whilst the gnats are annoying, they don't seem to cause any harm.

    Billericay - Essex

    Knowledge is knowing that a tomato is a fruit.
    Wisdom is not putting it in a fruit salad.
  • Mr. Vine EyeMr. Vine Eye Posts: 2,394
    @Pete.8  Hi, the thing is that we've never had a problem with them before despite having lots of seed trays and potted on plants indoors. I'm convinced that they came from this particular batch of compost because they appeared after that came into the house. The larvae must have already been in it when I potted the plants up. Because they hadn't been there at any earlier stages.

    It got to the point where it was a major issue, they'd spread to every room in the house regardless of whether there were plants or not. Getting in our faces at all times of the day. Proper plague.

    And that's despite following all the advice for reducing their numbers.

    If this happens again my wife won't let me have any plants in the house at all!
    East Yorkshire
Sign In or Register to comment.