Anyone heating their greenhouse in Fall temps?

[Joel_BC]

We've had a below-freezing night now and again over the last three weeks or so. We've got some kale and some lettuce (several varieties) in the greenhouse, and they will probably be okay for another week or so anyway. The kale probably will make it through the winter, actually.

In spring, we have early radishes & greens in the GH, along with starts in flats. We put a small electric heater in there (at the lowest setting) in April. Haven't done anything like that in fall, so far in any previous year.

What are you doing as far as supplemental overnight heat in your greenhouse?

If you are using some, how do you look at the economics of the electricity (or other fuel) involved?

 

[moolie]

No "supplemental" heat per se, in terms of powered heat, but we have heat sinks in ours. We use buckets of water and piles of bricks/cinder blocks that heat up during the day and keep the space around them warmer than the ambient air temp during the night. Our winter temps/conditions are way too wonky to do much else--it would be prohibitively expensive to truly heat the space when it is as cold as it gets here (and we only have a polytunnel at present, not a real greenhouse, so we'd just be throwing away money).

Our greenhouse is done now, but we probably could have kept greens going until early December as we've only gone down to around -10C so far, but we had quite a cold start to October, a couple of big snow dumps (mostly melted now with the recent Chinook) and between keeping busy with house guests and being out of town for a bit we ate it all before we got too busy to care for it. Still have parsnips in the garden that we'll need to dig before the ground totally freezes, we're hopeful that our cardoon will come back in the spring, and everything else is pretty much cleaned up for the winter.

 

[Joel_BC]

No "supplemental" heat per se, in terms of powered heat, but we have heat sinks in ours. We use buckets of water and piles of bricks/cinder blocks that heat up during the day and keep the space around them warmer than the ambient air temp during the night. Our winter temps/conditions are way too wonky to do much else--it would be prohibitively expensive to truly heat the space when it is as cold as it gets here (and we only have a polytunnel at present, not a real greenhouse, so we'd just be throwing away money).

Thanks, moolie. As usual, an upbeat and informative post.

We're using remay over the lettuce beds - but not with the kale.

I'd be interested to know more about how you've incorporated heat sinks in your polytunnel... I'm guessing, but thinking they're probably quite near where you had the plants themselves? Actually in the beds, dug into the soil some way? The heat sink principle makes sense. We had an earthen floor, up until this summer when I laid down some concrete blocks - but they run between our raised beds, so the influence would be pretty general and diffuse.

Perhaps I missed it, but I'll ask: did you upload any pics of the interior of your GH that might show where the heat sinks are situated?

Of course, as the air temperature begins to get consistently around the freezing mark, I don't see how heat sinks can pick up enough heat during the day to contribute anything at night.

 

[moolie]

Hey Joel, nothing very complicated--just 3 and 5 gallon buckets of water and piles of bricks close to the plants. Kept our tomatoes, bell peppers, and celery alive through a few frosts. We put old bedsheets over a few bigger tomato plants but some we left open at the top and both methods worked fine.

Trying to think of a permanent way to install the blocks/bricks (we have a pile of assorted bricks beside our house). At the moment we do have blocks along the curved side walls of our greenhouse that we plan to fill with sand, but as you say I'm not sure how much of a difference that will make once our daytime temps are below freezing.

Here's a photo I just took of the north-west corner of the greenhouse showing the blocks in place:

We had several 3 and 5 gallon buckets full of water placed around the plants we were saving from early frosts, but most have been emptied and put away now.

Here's an old photo of the greenhouse just so you know what the whole thing looks like--it is 10' wide by 8' long, height about 6' or a bit taller at the center.

 

[baymule]

Joel, I heat my greenhouse in the winter, but it is a whole lot warmer here than where you are! The greenhouse is a PVC frame wrapped in plastic with a small electric heater for the freezing nights. We just don't get a lot of freezing weather here. Lettuce, greens(turnip, mustard, collard, kale), broccoli, cabbage, onions, brussel sprouts, all live and produce all winter. I have tomatoes in my greenhouse so we can enjoy them all winter. I just have to keep an eye out for freezing weather and plug in the extension cord.

 

[Joel_BC]

Joel, I heat my greenhouse in the winter, but it is a whole lot warmer here than where you are! The greenhouse is a PVC frame wrapped in plastic with a small electric heater for the freezing nights. We just don't get a lot of freezing weather here.

Hmm... Yeah. Actually, it may not be as cold here - even in an ordinary winter - as you're imagining. In mid winter, our daily temps generally sit a degree or two below freezing during the day, and maybe 10-15 degrees below freezing at night. But not every winter night is that cold, although we can get a cold spike down to 0* F once in a while during winter. Still, I suppose it's probably a little colder here than where you are, baymule.

But compared with where I'm located, it is colder where moolie lives - in winter.

 

[moolie]

Lol, yup!

It's not predictable when we'll get the cold temps, but starting anytime from mid-November through April we can get daytime temps around -20 to -25 C (14C)-4 to -15 F) and night time temps down as low as -30 (same in C and F).

But more typically our winter daytime temps are around -10C (14F) and night time temps around -15C (5F).

Unless we have a Chinook (strong warm winds that roar down from the Rockies) which happens every couple of weeks or so, and then the temps can shoot up to "go outside in shirt sleeves" type weather for a few days.

So where most gardeners in "cold winter" regions can rely on snow cover for garden protection, we cannot due to our extreme freeze-thaw cycles. Mulch mulch and more mulch, and then just hope anything perennial actually makes it through

Sounds way worse than it is, as they say around these parts, "it's a dry cold".

 

[k15n1]

No "supplemental" heat per se, in terms of powered heat, but we have heat sinks in ours. We use buckets of water and piles of bricks/cinder blocks that heat up during the day and keep the space around them warmer than the ambient air temp during the night. Our winter temps/conditions are way too wonky to do much else--it would be prohibitively expensive to truly heat the space when it is as cold as it gets here (and we only have a polytunnel at present, not a real greenhouse, so we'd just be throwing away money).

Thanks, moolie. As usual, an upbeat and informative post.

We're using remay over the lettuce beds - but not with the kale.

I'd be interested to know more about how you've incorporated heat sinks in your polytunnel... I'm guessing, but thinking they're probably quite near where you had the plants themselves? Actually in the beds, dug into the soil some way? The heat sink principle makes sense. We had an earthen floor, up until this summer when I laid down some concrete blocks - but they run between our raised beds, so the influence would be pretty general and diffuse.

Perhaps I missed it, but I'll ask: did you upload any pics of the interior of your GH that might show where the heat sinks are situated?

Of course, as the air temperature begins to get consistently around the freezing mark, I don't see how heat sinks can pick up enough heat during the day to contribute anything at night.

If you want to build a solar greenhouse, there is general information here:

http://builditsolar.com/

 

[Joel_BC]

If you want to build a solar greenhouse, there is general information here:

http://builditsolar.com/

Thanks for that link, K15n1. Do you have a solar GH that you operate? If so, how have you handled thermal mass, heat sinks, etc? And how far into your cold season are you able to operate it without supplemental energy (electricity, propane, whatever)?

I doubt that we will build another GH. We might make modifications to the one we have, though.

 

[Daisy8s]

We just finished our greenhouse this week so I cannot tell you how our heating methods will work...I can only share what I learned from others and have implemented to try out.

1. I spray painted several large tubs black on the outside and then filled them with water. These will be both heat sinks and provide water for plants since I don't have running water out there. Personally I'd rather haul a lot of water on nicer days than a little water each day, and, providing these tubs don't freeze I can fill them on those nicer days.

2. Our greenhouse runs from east to west, and the back of the greenhouse faces the coop so, not only does it face the north but it'd also get a lot of shade. Therefore, since there'd be little light coming in on the north side we decided to make it a solid wood wall. Then, I painted this whole wall white so that it will reflect the light that comes in elsewhere. I think this solid wall will also help the greenhouse retain heat since the cold wind comes from the north and now that cold wind will hit solid wood instead of thin plastic.

3. Horse manure and lots of it! I sunk a tub into the ground and filled it with horse manure and worms in order to keep a worm bin going year round. I have the bin covered with a large board so I can walk over it and it takes up no space in the greenhouse. But, after just a few hours I was amazed at how much warmth was being generated (I was a little worried about cooking the worms!) It occurred to me that if I had a few tender plants that needed extra warmth I could remove the board, set the pots right in this manure, add some straw for insulation, and keep that warmth right in contact with the plant.

I don't know yet how often I'll need to renew the manure in order to keep it generating heat, that'll be an experiment. But, it's a perpetual system since I can remove the worm castings and use them for planting, remove extra worms and feed them to the chickens for winter-time protein, then just add more manure to the left-behind worms and repeat!

4. I'm contemplating two more options. a) I might paint all the wood shelving black--except I'm concerned this may make them too hot to touch in summer. b) I made a huge planting bed (12 in high, 18 in wide, 5 feet long) and put horse manure in the bottom 6 inches and then filled the rest with dirt. My plan is to plant things in there and add rocks and bricks between the plants. I just have this vague idea that a large, deep bed of dirt will retain heat longer than little flats and pots, but I have no proof of this.

These are my ideas. I'm interested in other's ideas, too.