Any time there is a change in environment the plants need to be hardened off - slowly adjusted to - that new environment. Moving from out of the house into hoop houses is still too big an adjustment to do it cold turkey. :)

Dave

I have used the row covers for years for different things. The row covers allow 85% of the light through and raise the temperature under them by about 2 degrees. It will protect plants with a light frost but if you get a heavy frost your plants will freeze. I suggest you plant only frost hardy plants that early. Why risk losing plants that are killed by frost.

Yes your plants will have to be hardened off so they get used to the UV light

Row covers can also be left on some plants to keep the bugs away. I use them over onions and carrots all summer to ward off the carrot rust fly and onion maggot. If they can't get to the plant they can't lay their eggs

Great advice all around. I will stage the little seedlings out into the cold frame and then under row covers as the weather indicates. I was really hoping the covers would protect more than 2 degrees, and now i'm glad I asked. Last year we had 17" snow on May 22nd, so will try to curb my enthusiasm when the time comes. Patience is so hard when the gardens are calling to me!! Thanks again.

That 2 degrees make a big difference in plant growth once it's on because it also warms the soil. The first year I got mine I wanted to test it out. I cut off a piece and covered 1 of 2 like varieties of perennials. I can't remember which variety but I know they were the same variety and about the same size. I put it on a little while before my frost date and left it on for about 3 weeks. When I took it off that plant was 3 times as big as the one left uncovered

I read about them in Eliot Coleman's books, and was interested in what he was doing both out in open fields and in his high hoop greenhouses. I figured with my northern climate and the challenges of predicting last frost dates it might be just the right thing to help extend the season. I have altered my seedling starting dates a little and will get them out into the cold frames about the time I get the row covers in place. Then when they are ready I can get them under the covers a little earlier than I would have felt comfortable previously. The experiment with identical plants covered and uncovered is so encouraging to me. I think this is just what I've been looking for! What other uses have you found for them? Do you extend the fall season with them? What plants have you successfully protected then? Thanks for your help!

Just thought I would post a little update about my original question, harden off in cold frame or put directly into the raised beds with row covers: I tried both. I am in far northern wisconsin, true zone 3. We were still getting wet snows 2 weeks ago and are still experiencing frosts. About 4 weeks ago I put row covers on my 4' x 16' raised beds. 2 weeks ago I moved my seedlings out into the cold frame, and that same day I planted several rows of lettuce and put some chinese cabbage plants and broccoli plants directly out under the row covers, with no hardening off. I had extras so was just experimenting. My row covers are agribond, not sure which thickness. The hoops hold the covers about 18" off the surface and I have the edges weighted down to prevent blowing off.
To my amazement, the lettuce is all up and growing, and the plants have shown no sunburn or ill effects of not hardening off first. I got brave today and planted a few less than cold tolerant plants under there like some tomatoes. I have cut worms so all of my tender plants get protective collars around them, but I haven't done anything else to protect them. So far a successful endeavor!

Nice update! Always nice to see experiments. I encourage it.
And encourage back-up 'insurance' starts/plants. : )
Those of us in northern climates need to try various methods as every spring can bring crazy temps and late winter-like storms. Prevents 'hysterical' gardening. Enjoy the challenges, makes it interesting. Accept failures and let it roll of with acceptance.
I noticed two different fabric weaves in my garden shed last weekend. Not planned. Just bought-it-when-i-saw-it. (A few yrs ago).
I may have to 'speed' plant a few things early this coming weekend due to work. (may be out of town a few weeks)
Might just hoop and lay over double or four fold a dozen toms and let nature/weather decide the outcome.

Frost predicted tonight and snow flakes tomorrow. Can't wait to see how the warm weather crops handle it under the row covers. Close to 70 predicted in 2 days. Spring is a crazy ride!