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Compost gnats on seedlings/pots with seeds yet to germinate

REMF33REMF33 Posts: 478
edited 4 February in Problem solving
I have them. Obviously I can't do the usual of putting gravel on the surface of the soil as seedlings are involved. I am assuming it doesn't really matter, but it's rather annoying as the pots are in my sitting room. Can I spray with soapy water? (Will this actually help?) If so, is it ok to do it when there are tidy seedlings involved?
I think it must be the seed compost I used. There is a similar probelm in the greenhouse with the hardy annual seedlings sown in the autumn. It's Sylvagrow.


  • FairygirlFairygirl west central ScotlandPosts: 46,064
    I don't think there's much you can do. It's when it's warm and wet they emerge.
    Possibly keeping the pots in a cooler room might do the trick - if you have one.
    It's a place where beautiful isn't enough of a word....

  • wild edgeswild edges The north west of south east WalesPosts: 7,483
    I had a batch of Sylvagrow last year that was swarming with gnats. Yellow sticky traps do help but manual removal of the adults is the quickest way. You can use a hoover held far enough away so it doesn't disturb the soil, or make/buy a pooter like I did
    The grubs in the soil can be treated with mosquito dunks dissolved in water apparently but I've never tried that.

    A great library has something in it to offend everybody.
  • FireFire LondonPosts: 13,910
    I used a hoover too and in the end I had such an infestation I used house moth spray in some rooms in the house.
  • REMF33REMF33 Posts: 478
    Ok thanks! I am trying to germinate chilli seeds so they need to keep them all warm. (Only one up so far. And this was my 6-seed packet...) The pooter looks kind of fun...!?! I have put a pot of cider vinegar with washing up liquid in it and have caught a few but it's not the solution (Um...) And there is a bit of a whiff. I am surprised it's such an issue in the greenhouse where temperatures have been getting down to well below zero.
    I might be trying a different brand of seed compost, come the big seed sowing fest that will begin next month.
  • Balgay.HillBalgay.Hill Posts: 607
    Don't buy the larger bags of wet compost that are usually stacked outside on pallets.
    Use the smaller bags of dry compost that are on inside shelves.
    Maybe more expensive, but i've found them to be more sterile, and i use them for house plants.
    Sunny Dundee
  • REMF33REMF33 Posts: 478
    This was a very small bag of seed compost, stored indoors in a small local nursery. Small enough for me to carry the mile home. Being peat free, it's quite dry. (I assume this is a thing as peat free multipurpose - different brands - I bought last year was similarly quite dry in texture.) I have never had this issue before. 
  • zugeniezugenie Posts: 471
    edited 4 February
    The dalefoot wool compost for seeds isn’t a dry one (assuming you aren’t vegan) 

    you could try nematodes for the gnats assuming the pots are inside?

    or diatomaceous earth on the surface of the pots rather than gravel. I will warn it goes a bit manky once it gets wet
  • REMF33REMF33 Posts: 478
    edited 4 February
    Will try to wool compost. I was wondering if it was any good. Thanks. Although the dryness was not really an issue. It wasn't dust-like (as some conventional MPC I bought in 2020 was ;) ) I am sure with peat free in general, it's just a matter of my learning how to use it.
    Will think about the diatomaceous earth. I didn't think it worked once wet. I am not watering them much but do need to everynow and again.
  • Jenny_AsterJenny_Aster Posts: 428
    Think I'd water the compost with a few drops of washing up liquid in it, maybe even dunk the whole pot in the solution then leave to drain.
    Trying to be the person my dog thinks I am! 
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