Sure you can. I have a cold frame and hoops (low tunnels) in Denver area and maybe today will go out and pick greens, maybe tomorrow and we've had 8-10 sub-zero nights, two episodes with multiple nights in a row. Not sure you can make green onions work without raised beds and insulation however. Check out Johhny's Seed's latest push and decide for yourself. You don't need to purchase a conduit bender, you can make your own. Also you can have spinach and cabbage and several other greens over the winter.

Dan

I am picking spinach out of my 12 by 18 hoop house. I have not put any heat in the building, just rowcover. I had tomatoes, cherry tomatoes, bell peppers and hot peppers upto November 16th. Would have been later if I didn't pull my plastic to save the structure from extreme snow load.

Go for it, you won't be sad.

If you calculate the fossil fuel used to build a small greenhouse and cover it with plastic, and compare that to the fossil fuel to truck the stuff from California to (in my case) Maine, then the greenhouse is definitely worth it.

We've had a fairly heavy year for snow, and mine has held up well to it. I've tried several designs, and this seems to be the one for me. It's a 16' x 24'wood frame, about 10' tall, made of 1x2 strapping and scrap 2x4 blocks. I've used a lot of scavenged lumber in it too. I've paid for the new strapping, galvanized screws, and little else. The foundation is cedar fence posts and 2x4s. The plastic is slightly used 6 mil greenhouse plastic. I've got about $100 into it.

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It was well worth it. I haven't made the best use of it. Others are harvesting spinach right now, but mine is empty. I'm about to start for the year though. I've got a couple small holes in the plastic and other air leaks, but it still made it up to 80° in there this morning. The ground isn't frozen except for about 2" down when you're within 18" of the east, south, and west sides.

I may be able to change that for next winter by burying some insulation down about 2' along all sides. I also want to bury some kind of metal (junk I'll pick up from the dump, either hardware cloth or old roofing metal) to keep the rodents out.

Dan

Very clever use of inexpensive materials Dan. Nice work.

I agree with arch. Impressive use of repurposed and found material.

I like the doubled arches, allowing an air gap for a second layer of plastic for insulation - maybe even allowing you to forgo a blower. Definitely insulate the ground around the perimeter and you should be able to go most of the year, if not all year.

BTW, here in Denver area I went out the other day to pick greens out of the low tunnel on the raised bed and had aphids on one of my lettuces. As I wrote above, we've had many cold nights, but it wasn't cold enough under the hoops to kill the little buggers..

Dan

It's not the temps that have hurt me (I'm in 5B) but the lack of sunlight. If I were to count all the hours of at least partly sunny skies we have had since Christmas, it wouldn't equal one full day. Sun-loving plants such as tomatoes are doing next to nothing, except growing tall.

Mike

In the US Southwest, lack of sun is rarely a problem. Where there is little sun, often the best you can do is hold things over until the light returns. Spinach will still overwinter in low tunnels, as will the cool season greens, but they will grow s-l-o-w-l-y.

Dan

LOOKS FANNN- TASTIC....

Comment from DH:
You mention that you used 1x2 strapping...However the bottom pic appears to be a 2x4 scrap sandwiched between 1x4's, instead of 1x2. Can you confirm and do you have any plans you can share?

Thanks...

The true dimensions of the strapping are 3/4" x 2 1/2".

There's a guy who does sell plans. I didn't use his. Google "stimson bow top shed" and you should find it. In these parts they're often used as boat storage structures. His version is tall to accommodate a sail boat hull with a deep keel. Mine is shorter to give less wind exposure and heat loss surface area.

The curve I used is tighter at the bottom than at the top. I used 14' strapping, which results in a truss half that's less than 14' long. You have to cut some off the ends to even things up, so you need to allow for that in the design. Planning on perfect precision while holding that curve would be too difficult.

I had a thread on building it, discussing it with my imaginary friends elsewhere. Link below.

Dan

Here is a link that might be useful: The New Greenhouse. Thread in the WoodenBoat Forum Bilge.

Reading the other thread: Is is double skinned? What do you find is the avg night temp? It is very impressive

It is single skinned. There are two collar ties that would make double skinning more complicated, but it could be done.

Since I did nothing after pulling the tomatoes, it didn't really get winterized, and day vs. night numbers aren't great. Last summer I just wanted it a little warmer and a lot drier in order to grow tomatoes. As it is, the low for the winter here has been -4° (so far, which is very mild for here) and the low for the winter in the greenhouse has been 7° (and I doubt it will get lower). With a few rodent holes around the foundation stopped up, extra layers on the north side, and the vent covered over I bet I could increase the temperature difference to 20°.

I just started spinach in the middle beds in the greenhouse. I covered them with scraps of GH plastic laid directly on the soil until they germinate. One local writer says using remay tunnels over the beds gets him a 10° gain.

Dan

I think you can work the second layer around those two ties if you took some time (maybe some foam insulation), and combined with some ground insulation you should be able to grow your cool seasons in winter if you get them started in fall, esp with hoops and row covers. Relatively easy. Again, well done.

Dan

I misspoke. I shouldn't have said Day vs. Night temps. I should have said nighttime greenhouse vs. outdoor temps. It can get really nice in there on a sunny day. It was 84° in there one day last week.

Thanks for all the appreciative comments.

Dan