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Winter temperatures: Greenhouse V Potting Shed

Hi. I have a greenhouse in which during spring, summer and autumn, I keep a large number of plants which are almost frost hardy, but not quite. (Cacti, Mediterranean plants etc) In winter at the moment I either have to keep them in the greenhouse and heat it when temperatures drop really low (very expensive and not really cost effective for the number which die) or move them into my conservatory (unsightly and very inconvenient).

I am thinking of getting a potting shed, thinking that in winter, the temperature would be just sufficiently high to keep these plants without any heating. In summer, of course I would use it for other purposes. Can anyone give some rough indication of the difference in winter temperature between an unheated greenhouse, and an unheated wooden potting shed which has half the roof and one side, plus the door windowed. If a rough indication can be given I would be able to guage whether my particular plants would survive OK. NB: I live in Essex.

Many thanks in anticipation. Alun

Last edited: 29 August 2017 12:09:14


  • PosyPosy Isle of Wight.Posts: 2,801

    I can't tell you the difference but I can say that I do not believe a wooden shed will be warm enough. The half hardies need as much bright light as possible but the cacti need to be dry and sheds are dim and damp. Greenhouse heaters can be fairly inexpensive and will protect the Mediterranean plants but even in Essex it may be too damp for cacti.

  • Posy, thanks for the suggestion, but would the shed really be damp? I would not need to water during the months the plants are in there, certainly as far as the trays of cacti (the main occupants) are concerned, so unless there is humidity derived from water seeping in through the wood, I think I should be able to keep it dry (I'd keep other plants elsewhere if necessary).

    And the potting shed I'm considering (Swallow - Rook ) is quite light - probably more than a third of the surface area is glass. If the minimum temperature reached in such a shed is at least 5 or 6 C warmer than an unheated greenhouse, then where I am, it should be OK temperature-wise. Cheers.

  • Singing GardenerSinging Gardener EssexPosts: 1,176

    I have a wooden shed with windows down one side and the temperature definitely drops below freezing in the winter. My prefab garage stays above 5 degrees but is too dark for plants. I have an electric heater on a thermostat in the greenhouse for my overwintering plants. I have quite a few plants that go in there now so use the whole of the greenhouse but when I didn't have so many I use to create an interior mini-greenhouse using bubble wrap and that was cheaper to heat.

  • Thanks for that Singing Gardener. It's not what I wanted to hear, because I was hoping the temperature in a potting shed like that would stay above freezing in this part of the world, but I'll take it on board. I'll have to think what's best for me. Cheers, Alun

  • PosyPosy Isle of Wight.Posts: 2,801

    Interesting. I think England's high humidity causes the damp rather than the nature of the shed. Central heating can support cacti which don't mind cold so much as wet.

  • hogweedhogweed Central ScotlandPosts: 4,025

    Depending on how many plants you have in the greenhouse, you could always make a greenhouse inside the greenhouse with bubblewrap, keeping the size to the same as the no. of plants packed in and lowering the roof height to just above them. It would be more economical than heating the whole greenhouse floor to ceiling. Or you could make a bubble wrap structure over a soil warming cable.

    'Optimism is the faith that leads to achievement' - Helen Keller
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