i have a 26x48 single poly high tunnel. you probably don't need the double layer of poly. when the temp is forecast to be below 20 i put row covers on the stuff in the unheated high tunnel. i grow greens and root crops in it all winter.
the inflated layer will help with wind and snow issues. it will also cut down the amount of sunlight.

randy41 thanks for the advice.Do you have snow or wind issues?
I'm in SD an we have pretty stiff winds at times.Do you use it during the summer?

I've got a double layer inflated greenhouse and a single layer sunroom. We have bad winds, about 40-60 mph about once a month and frequent lesser winds. Double inflated does help with the wind but I've held the single in place with an adequate system.

This isn't what I use but I think the Agra Lock would work very well. Wiggle wire might be good but haven't tried it.

Here is a link that might be useful: Agra Lock, wiggle wire

I was at a conference this weekend and the keynote speakers have 2 30 by 154 tunnels that have single plastic on them. They are in zone 4 in upstate New York. I have 6 tunnels and they all have single plastic.

What are your goals with your building? If you are going to be heating it, two layers with inflation will be helpful. If you are in a high wind area, then two layers will help on the
"Slapping" and "Flapping" of the plastic. I just have some patch tape on hand.

The way I look at it, we get too many storms that have hail. If I put up double plastic, then I am spending twice as much as I need to and it will take twice as much to replace it.

Jay

I'm planning to use the high tunnel for season extension to start with,get in earlier with tomatoes, cukes, peppers, etc and keep growing later into the fall.

Than later on I plan to start experimenting with growing greens during the winter months, to see if that's possible to do without heating just using covers and plastic. I don't want to heat the high tunnel.

How bad is the flapping? Can the plastic be tightened enough to completely eliminate the "Slapping & Flapping". I didn't realize hail was a problem. It seems to me that the inflated plastic would be better in that situation as the ballooning poly would provide a cushion for the hail and just bounce of instead of hitting a tight stretched plastic. Maybe I'm wrong.
Jay, what brand tunnels do you have?

If you get the plastic tight, the flapping and slapping isn't bad. I really don't see it as a problem. Small hail isn't going to cause a problem, if it is smooth. When I had a small tunnel, 12 by 18, we had some jagged sided hail. It sliced up the plastic pretty good. I just taped it up and called it good.

I have had hail marble sized up to almost golf ball sized just bounce off. Much bigger than that you will see damage.

Personally, I would just stay with single poly and save money.

"To see if winter growing is possible" It is possible and profitable. If you grow the right produce, winter growing is fun. This mild winter we took tomatoes to Thanksgiving and ate them until Jan 1. We have 6 tunnels full of produce that we are picking and selling now.

My big tunnel is from Stuppy's I bought it used. The other 5 are homemade.

Feel free to check out my website below.

Jay

Here is a link that might be useful: Jay's Jellies website

So were so you get your poly, pipe, and high tunnel hardware from?
g

How do tomatoes, cukes, beans and peppers survive in an unheated tunnel that gets into the 20's or lower. Even with covering, isn't it too cold? Don't they perish? What's the trick?

I ask because I have an unheated greenhouse that basically isn't used during the winter. Am I missing good growing times?

You have to cover things with row cover. That will help protect the tender vegetation. If you grow the correct crops, you can harvest and sell year around out of an unheated tunnel. My unheated tunnel got down to 27.3 last night, it was 11.3 outside. The crops inside will freeze, but they will also thaw out.

Here is a picture of one of my tunnels in early November.

{{gwi:8926}}

The extra cost of film isn't much compared to payback. I used to have only one layer on a 20x96 and 30x96 and was somewhat satisfied but after hearing all the facts on temp. benefits (which I don't have at my disposal) I readily recovered both with not just 2 layers but inner light dispersing,anti drip layer. An extension agent doing tomato research claimed that the light dispersing layer caused tomatoes to grow so well that it caused a potassium deficiency. Also the non-drip film seems to keep leaf mold incidence down.

I don't over-winter any crops but usually heat for all of March and most of April, after planting and often again for the end of October and November. I tried also using inner frame with fabric covering and also covering over short wire hoops but without circulation fan air movement I always lost plants at "Cold Spots". In zone 4 I'd be conserving every last bit of heat possible with the double outer cover. Just my opinion.

jrslick,

You said "If you grow the correct crops, you can harvest and sell year around out of an unheated tunnel. " What do you consider "correct crops"?

bob

Bob,

If you grow winter hardy crops you can grow year around in a tunnel and eat well all year around. Growing warm season crops, in the winter, is going to require added heat.

Crops that grow/hold for harvest well in the winter include, but not limited to the following:

Carrots, Radishes, Beets, Turnips, Rutagbegas, Parsnips, Green onions, leeks, spinach, lettuce, cabbage, Napa Cabbage, Bok Choy, Mustards, Tatsoi, Kale, Swiss Chard, Mache, broccoli, cauliflower, Arugula, and lots more.

Read Elliot Coleman, Four Season Harvest and you will get a better idea of what is possible.

In addition, with tunnels, you can get a jump on the season in the spring.

Jay

Here is a link that might be useful: Four Season Harvest

THX jrslick

Bob, you can also add anything that is winter hardy that goes dormant. I grow all sorts of herbs through the winter. Also overwinter tender perennials such as snap dragons for large plants in the spring.

Surprisingly, I've added Dill to my list. I would have thought they would not survuve but they are doing fine, if a bit slower growing.

This year I have played a bit and wa able to start cuttings of wave petunias and verbena. They do fine and even flowered when it was 2 degrees out.

My gh is 50 x 22 and double layered, no heat. I do not use row covers.

I have overwintered citrus trees in the GH. Died back to the roots when it got to -14F outside last year, but they have come back. Of course it'lll take years for them to get back to blooming size but i thought it interesting they survived.

Poppa

What kind of citrus?

Sometimes I think about what perennials I'd like in an unlimited amount of greenhouse space: everbearing raspberries, a couple peaches (marginally hardy outside here), figs, and maybe olives?? The list goes on every time I look at a One Green World catalog.