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Dahlia growers - which of these approaches do you vote for?

Hi all, I’ve just potted up my dahlia tubers which were kept in an unheated shed over winter. Now I have a choice:
(1) keep them indoors - they’ll get less light but consistent conditions - before hardening off once they shoot.
(2) leave them in a cold frame from the off (no greehouse). They’re the pots in the back half of the CF pictured - a removable lid goes back on the front section BTW. They’ll get more light, won’t get frost where I am, but temperatures will fluctuate more and I’m not sure if it means they’ll get too much warmth.
What do you dahlias aficionados think? No 2 is less work but I rarely hear of starting newly-potted dahlias in a cold frame.
Thanks as ever, Johnny



  • WonkyWombleWonkyWomble Posts: 4,509
    I would go for option b, as I like to breed tough plants. I have a greenhouse but unheated and the door is left open for a stray cat to sleep in. 
    I'm also growing dahlias from seed which are hardening off outside unprotected all only about 5 inches tall but doing fine.
    As an experiment I also left some sweet peas out through the snow,  hail and frosts, all have survived. Best of luck 👍😎
  • NollieNollie Posts: 7,512
    Option 2. The cold frame will be fine, just open it during the day. Mine are in an poly tunnel and the door and windows are left open all the time, unless a bad frost is forecast, then I shut it up at night. When they are sprouting well, usually coinciding with when risk of frost has passed, I move them outside.
    Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
  • AnniDAnniD Posts: 12,483
    Another vote for option 2  :)
    Smart coldframe by the way.
  • FireFire Posts: 18,996
    I kind of do the second - I keep my dahlia tubers in pots over winter and cover and fleece them to keep the frost off. I've never lost any over the years. Mine have just started sprouting - I'll take the covers off next week. 
  • newbie77newbie77 Posts: 1,825
    Option 2
    South West London
  • PosyPosy Posts: 3,601
    As long as the chance of frost has passed, outside is my choice. Do you intend to plant them in the ground later? I tend to start mine off in a frost-free GH but I will be planting them out any day now. They are just hardening off.
  • FairygirlFairygirl Posts: 54,895
    If they were big enough, and the conditions were suitable enough, they could be hardened off and outside for a while each day, and in a cold frame at night.
    Not if they haven't started shooting yet though, which is what you're asking in question 1. 
    Or did you mean they're already in growth a good bit?  I couldn't have them outside here without decent protection just now - not unless they had a decent amount of growth on them, and the weather was favourable enough, and they were inside at night for a good few weeks. They'd be shredded by the weather very quickly.

    If your temps are high enough consistently, they would be ok. Some people can leave them in the ground all year round.

    Sweet peas are different. They only need protection from rough weather, and severe conditions, ie heavy rain, wind and proper snow, ice and frost. They don't need warmth, the way dahlias do.
    It's a place where beautiful isn't enough of a word....

    I live in west central Scotland - not where that photo is...
  • KeenOnGreenKeenOnGreen Posts: 1,831
    Ours are kept in an unheated cold frame and greenhouse. Despite any frosts, they always survive.

    It can get very warm in cold frames and greenhouses at this time of year, it's important not to let your tubers dry out. We are regularly watering ours now, not soaking the pot, but definitely moist, especially now that we can see the leaves growing.
  • Hi all

    Thanks for the responses. I’ll go for option 2 with a few brought inside until they shoot by way of insurance and for comparison’s sake.

    @Fairygirl, the tubers were lifted from the ground late autumn wrapped in newspaper and kept in a cool shed over winter. They have just been potted up so they’re not shooting yet. Usually I keep them inside until they shoot, then start to harden them off.

    But this year I have my spanking new cold frame, and in central London it is warm and frost-free, so I’d love to be able to simply leave them out in the cold frame, taking the tops off during the day to air them. My main concern, as @KeenOnGreen pointed out, is that they may get too warm. So far they’ve just had a light sprinkling of water to start them off.

    So this is a kind of lesser-of-the-evils question - it’s cooler indoors (arguably), but there’s far less light.

    Cheers, Johnny
  • Thanks @AnniD, I’ll be posting about the ups and downs of creating an all-singing-and-dancing cold frame using polycarbonate in case it’s useful for anyone who comes trawling these forums in the future.

    AnniD said:
    Another vote for option 2  :)
    Smart coldframe by the way.

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