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Cosmos Seedlings Dying

Miranda 2Miranda 2 Posts: 14



I’m looking for some help with my cosmos seedlings. I’m tending to my joint studio’s container garden but I’m a very novice gardener this is the first time I’ve grown anything from seed.


My cosmos that were looking very healthy and strong and were responding well to hardening off have suddenly gone down hill rapidly. Their leaves are turning silvery and brown and then shivering up and dying.  The bigger seedlings are holding their own but the smaller ones have been decimated and I’m worried the bigger ones won’t last much longer.


I was wondering if it could be powdery mildew and if it was what the best way to treat it is?


Other possible problems I can think of is that they’re in miracle grow compost which I bought as wasn’t sure what to get but it’s horrible stuff with white mould appearing in the soil. I switched to Canna 50L Terra Professional Soil Mix Bag for my sweet peas but cosmos still in the miracle grow.


My studio room that I’ve been taking them in and out of is very hot and humid as I don’t have control of the studio heating and they’re being very slow to turn it off.  It seems worse after leaving them inside my room for a day when I was out.


Been keeping plants in separate pots but in trays together for ease of bringing them in and out. Maybe not enough air circulation.


I’ve been wondering if keeping them outside now would help, I’m in London and been hardening them off for 10 days.


Any advice much appreciated!  


P.S Could anyone tell me when it’s ok to plant out Black Eyed Susan Vine?







  • DovefromaboveDovefromabove Posts: 83,735
    My cosmos seedlings are outside in a little mini greenhouse a bit like a cold frame. If you can rig something up to keep the worst of the wind and rain off them I think they'll do better outside.

    Good luck image

    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.

  • DovefromaboveDovefromabove Posts: 83,735
    I put Blackeyed Susan out after the last frosts - early June here in Norfolk to be on the safe side image

    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.

  • I have mine outside and just pop half a plastic bottle over them at night as a cloche.

  • Kitty 2Kitty 2 Posts: 5,150

    Hi Miranda, they're probably struggling to cope with changing from a hot and humid indoors to the colder drier outdoor environment. Too big a difference in temperature.

    How big are they? If they're only small its still too cold to go outside permanently.

    Won't be putting mine out for a few weeks yet (sown first week in April).


  • PosyPosy Posts: 3,601

    Some cosmos are tougher than others. It has been much too cold here to put any out, even during the day. Mine are in a frost free greenhouse. I had to bring one variety into the house because it was still too cold. If your plants are cold they will begin to look pale - yellowish - and then shriveled but it could be the hot/cold aspect. Aim to get them used to small changes of temperature first and remember that a cold breeze can really knock them back.

  • Miranda 2Miranda 2 Posts: 14

    Thanks for all your replies! Just double posted this by accident on another thread as didn't get any alerts to say you'd replied.

    Sounds like maybe it is the temperature jump. It's a battle between the drafty end of the building and our end between having the heating on or off. We're losing unfortunately.

    The only other thing I'm worried about is that there appears to be quite a lot of white mould in the soil. The miracle grow bag says this is normal but doesn't seem quite right. Just concerned if it could be a bacteria problem if I have them next to my other plants. I'll upload a couple of pictures below. 

    Thanks for the black susan advice. We're pretty sheltered where we are but it still feels pretty cold at the moment especially at night. Don't have any greenhouse or cold frame and very much on the hoof urban gardening, we've made all our raised beds out of old pallets. i used bubble wrap to keep them protected over night this weekend, but looks like very low temperatures over next few nights.









  • Miranda 2Miranda 2 Posts: 14




  • Miranda 2Miranda 2 Posts: 14




  • Miranda 2Miranda 2 Posts: 14




  • Miranda 2Miranda 2 Posts: 14



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