While running an errand this morning I scrounged a free, clean, 55-gallon steel kerosene drum. My first thought was to use it as a rain barrel, and indeed I might. But then I had a thought.
Filled with water, this drum would create a substantial thermal mass. In the open air, how useful would that be in creating/sustaining a microclimate in my garden, for protecting plants (around the base of the barrel, or on top of it in containers) from frost and keeping them a bit warmer at night for faster growth? (Where I am this would be primarily useful in spring and fall; if anything we have too much warmth in the hot season, even at night.)
I know the drum would be very useful for stabilizing temps in a small greenhouse, but I don't currently have one. But I was thinking that protected seedlings (in, say, mini-greenhouses made from 2-liter bottles) could be put out several weeks earlier if they were huddled close to this sun-warmed-in-daytime thermal mass.
Anybody done this? Is it useful enough to "waste" a good barrel on?
I suspect in open air it would be pretty ineffective. I have some 55 gallon rain barrels that I use to slow water whenever it rains and they all froze when we had a couple day cold snap that got between 20 and 25 degrees. That is a cold snap for Portland so take that for what it is.
If you could isolate it from the wind and get it some sun it might do more good than mine did.
EDIT::: I suppose if it doesn't freeze through completely a 32 degree mass is better than a 0 degree open air. I still think to get some good effect out of it you'd need some kind of shelter to insulate the cold air from the mass, but I'm more than open to being proved wrong .
If you drape a clear tarp over it (make it the "tent pole" in a teepee), it does help.
If it has the lids, you can fill it then lay it on its side and surround it with straw bales to make a cold frame. That is VERY effective. Partially bury it so you don't have to make the cold frame too tall
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There's no doubt that a thermal mass warms the air around it, which is much more effective if that air is captive and can't waft away on every breeze, to be replaced by more cold air.
But there's at least a bit of direct radiant heat from the thermal mass, affecting air (which probably blows away to little benefit) and plant tissues (which don't blow away) alike. My interest is in all those nights spring and fall when the air temp drops below freezing, but only for an hour or two. (These tend to be still air nights, too.)
Ultimately nothing to do but try the experiment, I suppose!
I am embarrassed to say that I only observed one of my barrels, and it was one without much life around it. If I'd have walked around to the other side of my house I could have observed what my rhodedendron (which hides one of my barrels) looked like during the freeze. Curses.
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