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hardening off advice requested

REMF33REMF33 Posts: 720
I have grown a lot of flowers this year having grown mainly veg for years, including some hardy annuals, such as calendula, penstemons and am a little unsure of myself regarding when and exactly how to harden things off. Can I start hardening such plants off now? And if so could they go straight into a cold frame or do they need something more gradual? (i.e. out in the day and back in at night.) They are currently in an unheated lean to. It has been down to 4C in there, although since I last reset my thermometer a few days ago, the lowest it's got has been 9C.
The calendula are about 7 inches tall. Penstemons not far behind.
I am in SE London. Nothing lower than 7C forecast for the next 10 days.

I also have some Rudbeckia hirta that are pretty strong and getting quite big... (and I desperately need the space!)


  • REMF33REMF33 Posts: 720
    While I am at it, is it too early to harden off tomatoes? I am going on holiday in a couple of weeks so it would be good to get them out by then. Some of them (in 18-20cm pots still so need potting on) are flowering.
  • WilderbeastWilderbeast Posts: 1,415
    If you had a cold frame that would be fine you could also start lifting them outside for the day in a sheltered spot then back in at night. I'm not obsessed with doing days and days of hardening off and after 5/6 days I'd have them out (dependant on the weather). I'm not sure on your Tom's as I'm from the frozen wastes of Yorkshire and we are getting frosts most nights. 
  • REMF33REMF33 Posts: 720
    Thank you very much. Will start doing that with the hardy annuals.
    re tomatoes, I am really tempted to start soon with them as some of them do desperately need potting on. 
    The guide for last frost date here, is, apparently, mid April. We have not had a frost here for a while, but it did dip down to 1C about a week ago. I chose to go on holiday in the third week of May rather than the usual July or August partly to avoid watering issues (cat sitters do it, but understandably don't have time to do it very thoroughly) but I didn't take into account hardening off and monster-sized flowering tomato (and tomatillo) plants! (I suppose I must have sown them a bit too early.)
    Thanks again.
  • This is useful; what's the watering regime when you're hardening the plants? I've been doing nights in the shed and day outside but now has min temps are consistently 6/7C I'm just going to leave them outside.
  • DovefromaboveDovefromabove Posts: 86,996
    I wouldn't leave toms, squashes or runner beans outside until night time temperatures are consistently above 10C and preferably mid teens  :o

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

  • cats_and_dogscats_and_dogs Posts: 71
    edited May 2021
    oops, replied to the wrong post!
  • REMF33REMF33 Posts: 720
    I think below 10C they stop growing but would otherwise be ok? Over the next 5 days, the lowest night temperature (met office) forecast is 7, but it's 10 -12 most nights. It could conceivably be consistently 10 and over by the last week of May so I could start hardening off sooner rather than later, or at least have them outside for a it during the day so that I feel less hemmed in :) But I think realistically I am not going to risk putting them out it until I get back from my holiday, just in case. Probably easier or my cat sitters to water in the sitting room too. 
    Of course today it's too windy to want to put anything out.
    My current jungle situation:
  • DovefromaboveDovefromabove Posts: 86,996
    In my experience, if the tomatoes etc sulk at 10C and below, it takes quite a while to get them going again ... they get really set back.  I've found it better to put up with the inconvenience of keeping them indoors just a bit longer :)

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

  • REMF33REMF33 Posts: 720
    They may also sulk from being pot bound though? But I shall follow your advice and keep them in until the bank holiday weekend, assuming it's warm enough then. This is just the sitting room. It doesn't look in the photo as it does in reality! I am going to have to pot on the ones on my kitchen window sill soon too.
    Lessons have been learnt... :)



  • DovefromaboveDovefromabove Posts: 86,996

    My studio ... and I started well after you did. 😉 

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

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