I have a question that may or may not be stupid. Let's see how the answer goes. I have just made a cold frame and am about to build another. I'll be putting seed sowings and some cuttings and all the usual stuff in there. Would it be a brainwave or ridickilis to put black painted bricks in the bottom to act as little radiators for night time? The temperatures got to -7 here for over a week last year but it was bright sunshine every day. My theory is they would heat up during the day and stop the whole thing freezing solid.
Heating up during the day is the problem isn't it? You'd be making a solar powered oven. I once read about Dick Strawbridge's greenhouse project where he built a load of thermal collecting stuff into the ground underneath with a black radiator to circulate air or water through it. I've no idea if it worked though.
If you can keep your head, while those around you are losing theirs, you may not have grasped the seriousness of the situation.
Looks like we might have a spurriment in the making @wild edges. You say oven but with the wittery wattery sun at that time of year it wouldn't be good for biscuits; just enough to take the edge off...and removable and only some of the actual Radiator surface would be exposed.... When Dick was Richard he was a good friend of mine. 😉 If he did it it probably worked.
I had a cold frame on concrete slabs, tucked in a corner against house walls @plant pauper . Made no difference to keeping certain plants alive, but the slabs wouldn't have heated up well enough, so it was the wet atmosphere that was more of a problem. If cold frames are sitting on soil, it doesn't always work either, because the wet cold is what's damaging due to it creating too much mould making moisture in them, so they need to be open, which then doesn't suit a lot of plants either. I found a gravel base better for my cold frames, but it would still depend on what you were trying to overwinter. Anything less hardy/tough just stays inside my house, or I don't grow it! All you can do is experiment. Minus 7 isn't too severe though. It's more about prolonged cold, or prolonged heat that makes the difference to small plants. A pit under it with organic material might work well enough as long as you opened the cold frame during the day.
It's a place where beautiful isn't enough of a word....
I live in west central Scotland - not where that photo is...
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I have just made a cold frame and am about to build another. I'll be putting seed sowings and some cuttings and all the usual stuff in there. Would it be a brainwave or ridickilis to put black painted bricks in the bottom to act as little radiators for night time? The temperatures got to -7 here for over a week last year but it was bright sunshine every day. My theory is they would heat up during the day and stop the whole thing freezing solid.
When Dick was Richard he was a good friend of mine. 😉 If he did it it probably worked.
http://www.reuk.co.uk/print.php?article=Solar-Greenhouse-Heat-Sink.htm
I found a gravel base better for my cold frames, but it would still depend on what you were trying to overwinter. Anything less hardy/tough just stays inside my house, or I don't grow it!
All you can do is experiment. Minus 7 isn't too severe though. It's more about prolonged cold, or prolonged heat that makes the difference to small plants. A pit under it with organic material might work well enough as long as you opened the cold frame during the day.
I live in west central Scotland - not where that photo is...