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Overwintering in cold greenhouse

BulbbankruptBulbbankrupt Posts: 6
in Plants
Hi everyone, possibly this has been covered before but I can’t dig it up in the old threads. I have a small greenhouse (waist height as opposed to walk in, so maybe a cold frame greenhouse hybrid really) and am wondering about overwintering various cuttings (salvias, agastache, santolina) and tender plants (lobelia, Californian poppies) in there.
Obviously the success somewhat depends on the weather this winter but has anyone tried increasing insulation in their greenhouse using bubble wrap or fleece or something else? I’m in London so it’s not usually too cold (she says…)
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  • CeresCeres Posts: 2,698
    I gave up the bubble wrap insulation decades ago because it tended to make the greenhouse dank and a great place for mould growth. I used the vast cylinder of bubble wrap for many years to pack parcels and the plastic fixings are still in the greenhouse for holding tomato plants to the frame and suspending home-made blinds (not much used this sunless year). So......a waste of money as greenhouse insulation but has many other uses.
    It does, as you say, depend on the weather and in a really bad year even insulation won't help the plants.
  • wild edgeswild edges Posts: 10,497
    Insulation is only really required to keep down heating costs. In an unheated greenhouse the inside temps will be much the same as outside just without so much wind chill and with lower frost risk. The main reason is to regulate weather damage rather than keep things warm. You need to keep air flowing in greenhouses too so the cold air is going to get inside anyway.
    If you can keep your head, while those around you are losing theirs, you may not have grasped the seriousness of the situation.
  • AnniDAnniD Posts: 12,585
    edited August 2023
    I'm in the South West UK and have a small lean to greenhouse up against the house wall.
    I definitely wouldn't use bubble wrap, as previously said it just causes a build up of moisture in such a small area.
    During really cold periods l use a layer or two of fleece over any overwintering cuttings (shrubby salvias, penstemon, that kind of thing), but so much depends on the weather. 

    In previous years l have had a pretty good success rate over of 75% survival, but last year l lost the lot. I think the really cold spell in December had a lot to do with it, the cuttings weren't really acclimatised to the cooler weather and temperatures that low were too much of a shock. 

    You may as well give it a try, you have the "greenhouse" sitting there, and being in London should give you a mild micro climate :) .
  • BulbbankruptBulbbankrupt Posts: 6
    edited August 2023
    Thanks @wildedges and @Ceres I’m sure you’re both quite correct - it was more in hope rather than expectation that I asked  ;)
    Maybe I need to start warming my other half up to the idea that all the window sills will be occupied this winter  :D
  • BulbbankruptBulbbankrupt Posts: 6
    Thanks @AnniD maybe I’ll spilt my babies in half, and try half inside and half outside with some fleece for company. Sorry to hear you lost everything last winter! It was a real cold one by recent standards. I guess we could try to keep a beady eye on the forecast, although I find life often gets in the way and by the time I stage an intervention things are too late!
  • tigerburnietigerburnie Posts: 131
    What I do is "plunge" the pots in the greenhouse border soil, then cover them with a fleece blanket, works for me in NE Scotland
  • JennyJJennyJ Posts: 10,576
    For me, salvia cuttings that are well-rooted and in individual pots overwinter fine in a sheltered spot outside near the house wall. They can lose their leaves in a cold spell just like the full-sized ones but they regrow in spring, so yours should be fine without extra insulation.  Even S. patens which is supposed to be a more tender one was fine last winter.

    Doncaster, South Yorkshire. Soil type: sandy, well-drained
  • BulbbankruptBulbbankrupt Posts: 6
    That’s good to know, thanks @JennyJ
    Fingers crossed there’s some more warm weather and good root growth now before it gets too cold!
  • BulbbankruptBulbbankrupt Posts: 6
    Very interesting @tigerburnie. When you say the greenhouse border soil, is that the soil your greenhouse is built over? Mine’s on a deck but maybe I’ll try similar with some large pots and fleece.
  • tigerburnietigerburnie Posts: 131
    Bulbbankrupt said:
    Very interesting @tigerburnie. When you say the greenhouse border soil, is that the soil your greenhouse is built over? Mine’s on a deck but maybe I’ll try similar with some large pots and fleece.
    Yes my greenhouse is on the soil, this allows me to protect the roots from getting frozen up here in Polar Bear country, using fleece round your pots will help
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