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Frost free greenhouse?

In last weeks GW, Monty said he puts some plants into a frost-free greenhouse, also implying it is unheated! However do you ensure a frost free greenhouse without some heating? Last year I insulated a sub-section of my uninsulated greenhouse with bubble wrap, but the frost still got in.


  • AnniDAnniD Posts: 11,929
    edited October 2022
    The subject of bubblewrap in greenhouses came up on another thread, and someone mentioned using a tealight under an upturned flowerpot. Y'er tis.

    Personally l'm not sure just how effective bubblewrap alone would be at keeping it frost free in a prolonged "Beast from the East" scenario, but a lot depends on its size, location in the garden, whereabouts you are in the UK etc.

    I watched an item on Alan Titchmarsh's Sunday morning show where paraffin heaters were suggested as a cheaper back up than electric heaters in colder spells. One problem with using these is an increase in moisture levels. Added to which, l've no idea where you can buy paraffin these days.
  • FairygirlFairygirl Posts: 53,942
    I think there was a recent discussion about this @sandyv.
    Yes- unheated and frost free aren't necessarily the same thing, although it's often implied.
    Mine certainly wouldn't be frost free without having some form of heating in it, and although it's a small one, and not as protective as a 'normal' greenhouse, your local conditions and climate make a huge difference. 
    Many people use fleece for plants, or even a small plastic greenhouse within the main one to ensure temps are kept above freezing. It may come down to experimenting with what you have, and of course - a lot depends on the type of plant.  :)
    It's a place where beautiful isn't enough of a word....

    I live in west central Scotland - not where that photo is...
  • punkdocpunkdoc Posts: 14,346
    Frost free unfortunately doesn't mean unheated. Where I live, I would regularly need heating to maintain frost free temperatures, and there are far colder places than here.
    How can you lie there and think of England
    When you don't even know who's in the team

    S.Yorkshire/Derbyshire border
  • Monty can afford a wooden double glazed (heated?) greenhouse.
    To heat a greenhouse you either put no effort in and just throw money at it, or put a lot of effort in and do it very cheaply.
  • wild edgeswild edges Posts: 9,909
    I've seen experiments using a combination of insulation, thermal mass, solar heat collectors and solar powered fans to try and retain heat without using fuel. Some have been buried into the ground to reduce the amount of exposed walls. I'm not sure how successful these have been in the worst winters though. Personally my tender stuff comes into the house and the rest has to tough it out. There are worse ways to waste energy these days but the days of heating greenhouses for private use are probably numbered now.
    Tradition is just peer pressure from dead people
  • I live in a cold area but have managed to keep my greenhouse frost free relatively easily. I have just a small fan heater and bubble wrap the roof and all the glass walls, but what helps most is that it is a lean-to with a solid stone wall behind. Whenever the sun shines, even in winter, the stone warms up and acts as a 'hot water bottle' heat reserve overnight. I set the fan heater at the lowest setting and many nights it doesn't need to come on at all. It comes into its own when we have a really cold spell though: we had -12C for two weeks once!
    Recent winters haven't been nearly as bad, but it is the unpredictability that makes life difficult. Last year I tried to manage without the heater, but lost some pelargoniums. This year I will bring them into the house. The other plants, mainly fuchsias and salvias, proved more resilient. :)
  • Nanny BeachNanny Beach Posts: 8,586
    When we moved here, the top green house had a heat may system, electric cables,over a bed of sand,a wool mat,to put the pots on. I understand it's pretty cheap to run. Yes, Punkdoc you're correct,in the very depth of winter,we have a little electric tubular green house heater,on overnight (Economy 7) thick bubble wrapped walls plus an extra layer thrown over the plants,and we're in the mild SE.
  • Have been looking into getting a better greenhouse recently as the polytunnel I use is a bit worse for ware. Getting by OK with just bringing things into the house but the idea of a passive greenhouse using water tanks or other thermal mass to store heat from the day, insulation on the north facing side and preventing drafts seems like it could be an interesting project and might try build one. I found a good lecture presentation about building this type of greenhouse here.

    Happy gardening!
  • nick615nick615 Posts: 1,458
    Endorsing Buttercupdays I understand (never tried it as I don't have a greenhouse) that plastic containers full of water and painted matt black, will absorb enough solar heat during the day to keep the worst of the frost off at night.  His 'lean to' arrangement also lends itself to a row of vertical 'organ pipe' plastic pipes, suitably sealed and filled, but standard models are less suitable for this.
  • There was a couple of mentions tonight of his heated greenhouses so I wouldn't get too excited.
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