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greenhouse frost protection/heating

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marcros

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I have a very small greenhouse (actually a tall cold frame) about 6ft x 2ft footprint, 4ft tall (bottom 12" is wooden). It isnt bubble wrapped but I plan to do so before the first frost.

I want to protect the contents from the frost over the winter rather than to try and keep it at full growing temp all year. It will be used to protect some seedlings for planting out next year and for storage/protection of some tender plants until they can go back out.

I have an external socket, so I think that a small electric heater is the way to go (with an rcd).

is this enough? Dimplex Thermostatic Tubular Heater IPX4 1ft 40W

alternatively there are small paraffin units, but I am more concerned about not having paraffin when I need it, the flame going out, etc. I have seen things made with nightlights and flowerpots, but again I am slightly concerned that if it goes out one night, everything could be wiped out as a result.
 

Trainee neophyte

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Depending on how much room you have, thermal mass is the way forward. Big barrels of water will help keep the temperature static. This will work with or without a heater, and will help you keep hold of any solar energy you might pick up during the day.


Other fun methods involve moving the compost heap indoors or making a cob wood stove batch heater. I like the water barrel plan because you can move them out in the spring, when you no longer have room for them.

Edit: I have now read your OP, and feel a bit silly. No room for thermal mass, obviously. My excuse is that it is a tad early. Any chance you could put your seed trays on top of a barrel? Other than that, bubble wrap insulation would be the obvious fix, wouldn't it? Incorporate it into the frame, so you still have access. (I'm not helping much, am I? )
 
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clogs

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I use a tiny oil fired rad in my caravan to keep it dry over winter....it's prob 16"x16"x 5"......
u can dial the temp right down....I keep it around 5deg.....
bubble wrap on the glass as well will help....
 

Tris

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What species are you trying to overwinter?
Pelargoniums/geraniums want to be 8 degrees C or above, fuchsias about the same although the roots will survive if the top growth gets frosted.
If your seedlings are biennial they tend to be pretty hardy anyway.

I'd suggest putting polystyrene insulation around the insides with a double or triple layer of fleece over to roof it then the dimplex heater should be OK.
Paraffin heater in that small a space will produce a lot of water and then you'll be more likely to lose the plants to fungal disease than cold.
 

Robbo3

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After insulating, if you find the tubular heater insufficient, perhaps a divider to make two sections.
 
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