My friend uses unheated cold frames to extend the season for fresh veggies. Last harvest was Dec 15, 2012 and she plans to start up again in Feb when the days start getting a bit longer. Dec 15 was a high of 5.5ºC/22.1ºF and low of -10ºC/14ºF
I hope she does a workshop.

Bravo for your friend!! I love cold frames. I use a cold frame as well and have a portable/moveable one although was not able to use it this year due to illness. Everything got put on hold. Here people sometimes use basement window wells to achieve the same thing, especially in an older house. Sample below:

http://www.everchanginggarden....

Sounds like a great idea. I wish I had a cold frame.

Mine is "portable" and lightweight but sturdy. Works well for me. I don't have basement window wells or a large cold frame set-up so the smaller one meets my needs. It's also nice to be able to move it to cover things in the ground.

How effective do you think a low hoop poly-tunnel is, as a cold frame?
Assuming the long axis ran East-West.

Does a cold frame totally need the bottom 6-10" as an insulator like thick wood? It always seemed to me that, with a low sun angle, that would guarantee shade when plants most needed light and warmth.

I set up some low hoops, then a tent, where I had a bed I wanted to keep warmer. It was a somewhat sunny spot in the summer, but NOT in January! I can confirm that a mostly-shady plastic-film tent is indeed a COLD cold frame.

(But sealing some leaks better might at least get the forst to melt off the film faster!)

Not sure Rick. I asked my friend to write a little article on her cold frame experience and pointers for our garden club.
This is her 2nd year of growing in late fall and winter.

I've started making note of varieties that people call "very cold hardy". Those are what I'll try first, well, other than plants that have overflowed my light shelf and need to go SOMEWHERE to make room for others.

Personally, I think the hoop frame would probably be fine in your climate. There are differences in a cold frame and a hoop frame. Hoops tend to catch more wind, and, no, you don't need the bottom wood. IMHO, cold frames are better at heat capture. I have heard that light capture can be more important than heat capture and the hoop frame would seem to have the advantage there. Just IMHO.

Ha, I have not been here in an age and there is my photo, what do you know! I used the different kinds of cold frames for different purposes. The transparent ones and hoops are great for wind protection, capturing more heat from the sun, and warming the soil quicker in spring. They really speed things along in the spring and summer for sure. Here in zone 3, I use wood frames lined with thick insulation to keep things alive and growing far into the winter. And yes, I use the most cold hardy varieties of the the most cold hardy vegetables. I just find it a challenge to see what I can keep going when it drops to minus 25, which it does here.

Theresa,

That is an awesome picture of you with your fresh winter harvest. Thanks for the extra info on your successes.

Thanks!

Capturing heat and warming soil in spring (and keeping the rain off) are what I most want. Also, holding seedlings that I started inside while spring is still yo-yo-ing between 30 and 70.

Wind is rough on hoop frames and plastic here. That's the "new tornado alley" for you. Glass and heavy and anchors in the ground are what works here. We don't have anywhere near -25 so things perk along nicely in the lighter weight cold frames without wood and insulation.

I applaud you for going for it, Theresa. I don't know that I would in your climate. Bravo.

Obsessive? Who me? Well maybe a little.....