poly tunnels

Any of you built or used poly tunnels? I kind of like some of the ideas in eliot colemans book on gardening such as: using rebar slid into pvc for frames tying the frames to a purlin with rubber from discarded intertube. Possibly sliding the entire structure over 2-3 differant beds. Using row cover or cold frames inside the tunnel to lower the need for heat heating only to keep plants above freezing staying away from heat demanding plants like tomato in the coldest months. Adtionaly in warmer weather i may want to use screen ends to keep insects out humidity in and temps down as much as possible i live in zone 6 and could come close to no heat in most years maybe a few days of heat and should be able to use winter for salads any brascia carrot pea beet potato. As previously stated i would just foget the tomato eggplant pepper corn squash bean etc. december jan feb are realy the only realy cold season here. warm crops could probably survive the rest under poly tunnel or outside in summer. I am thinking about a 10-12 foot wide 6-7 foot high whatever the 20 foot ribs would give maybe about 12-20 foot long.
It is quite windy here and i am thinking maybe increase the rib size by at least 1 diameter maybe 2 over standard and possibly uising closer spacing as well as nylon grid reinforced plastic that is often used around here to tent construction sites for brick work in winter. Since it takes 2 ends no matter what i would likely go the 20 ft long.

[Windy in Kansas]

Zone 6 may be enough warmer to give more of a wet snow or ice than a zone 5 location would. I have lived in both zones and found the snow in zone 6 to be much wetter and heavier.

Having said that, a local greenhouse decided to add additional units. They built their own frames to save on costs. End result----they collapased under the snow load the first year. These were double layer inflated poly units. Because of the air insulating pocket the snow doesn't melt off like you might think. Even though the poly is slick the snow will build up. What I found was that slapping the inflated side would usually break the snow loose and it would slide off to the ground where it could be removed to prevent build up there.

I do like what I read recently in several books about growing during cold weather. I think we should probably be eating broccoli, cabbage and other such plants much more than we do. They do well in chilly environments.

Best of luck and keep us posted on your results.

i am down near wichita and for the last several years we have seldom had snows that could have collapsed anything. we normally get wind and that is more of an issue than snow load the wind will make the snow drift but seldom allow much piling i may have to dig to get any light to speak of after a heavy snow but don't anticipate snow load to be near the problem of wind load. we have averaged about one snow in the 3-12 inch category per year for the last 10 years. i would say about a third of our snow is wet but often if any quantity is involved it is over night and is mostly dry. sometimes a couple more 0-2 inch snows per year. More days than not we get up in the 40's for daytime highs during the winter months. getting rid of heat and staying tight over night may be the biggest challenge.

[Mike in Ohio]

We use plastic tunnels (no heat) over our raised beds. We only use single 10 foot PVC pipes on our 4 foot wide beds. So, not high enough to stand within. We are near Cleveland OH and we will still be picking tomatos in late november.

Greens like Kale overwinter quite nicely. I haven't totally overwintered root crops like carrots and turnips but they have kept nicely till late December/early January.

I've thought about larger ones but with the small ones we don't have to worry about wind load, snow load, whatever. At some point we plan on adding a glass greenhouse against the south end of one of our barns.

Mike