Our growing season up here is very short. Spring comes late and is usually cold. Fall arrives early and is usually cold. So in order to try to extend our gardening season, we need help of some kind. (A 50' x 100' heated greenhouse would do the trick.)
We have twenty-six 4' x 8' raised beds that lend themselves to having a 4' x 8' cold frame set on top of the wooden bed frames. This enables us to add weeks to both the beginning and ending of our short "summer" season.
We don't put cold frames over all the raised beds but we do use them on about half the beds especially for starting crops in the spring.
A couple of months ago, Jordan of Blueberry Hills Homestead in New York asked me if I would do a post showing the construction of our cold frames. (Good thing the dear lady said there was "no hurry" as I'm just now getting around to this posting and pictures!)
This is a picture of one of the first cold frames we built. It's shown here sitting on top of one of the raised beds. We built them to slope slightly to the south. The back is 12" high, the front (south end) is 8" high. We used solid wood for the four sides, and it is heavy as heck. Hurtfully heavy. The handles on each end are for ease (ha!) in moving. Since I rotate crops in each bed each year, not the same bed will end up with a cold frame on top of it each season. The cold frame comes off many beds as soon as the weather settles. Also, we store all the cold frames stacked in one area out of the garden for the winter months.
You can also see the arm that holds the cold frame top in various degrees of open or closed. When the top is up more than halfway, it tends to act as a sail that gets hit by the frequent strong winds we have. Therefore, we found we had to secure the cold frame in some way to the raised bed. After trying a couple of methods, the simplest turned out to be good old baling twine tie-downs.
This is just a shot showing the basic construction of the tops of the cold frames. For our first tops, we used rigid, double layered, clear, fiberglass panels. They, too, added to the weight of the cold frames, so then we went to special UV treated flexible (heavy, strong) plastic. This was much lighter and so far has held up well. (Besides being heavier, the fiberglass panels tended to be brittle and crack in cold weather.)
To hold the tops open at various positions, we use a 1" x 2" length of wood bolted to the cold frame side (so it swivels), holes drilled in the 1" x 2", and holes drilled in the side of the cold frame cover. By inserting a good-sized nail through the hole in the 1" x 2" and into the hole in the cover frame (one 1" x 2" arm on either end of the 4' sides), the cover stays securely in position.
After a couple of years of grunting, groaning and straining lots of muscles moving the wooden-sided cold frames, we got a smidge wiser and decided that (duh) if the plastic on the lids made the cold frames lighter, why not use plastic on the four sides? (Double duh.) So we've started replacing all the old frames with new ones made of plastic instead of solid wood.
This gives an idea of possible framing for the plastic covered frames.
We've experimented with different heights for the newer plastic covered cold frames. This one (not being used at the moment) is 3' high and we had it over a bed of tomatoes last year. Big drawback found: By the time it's on top of a garden bed (about 12" high), it's too danged high to reach over and into to pick the tomatoes! We used it this year with a shade cloth lid on top to try to discourage cabbage moths from getting to our broccoli. (Didn't work.)
Besides the slanted cold frames made with the plastic sides, we've also made a few "risers." These are level (no slant to their framing) boxes we use to give more height for plants to grown in. The riser goes on top of the garden bed, then the cold frame goes on top of the riser. Our risers are 12" high. The cold frame in this picture is 18" at the back side and 12" at the front (south) side.
These are the four remaining beds protected by cold frames in the garden today. They're covering cherry tomatoes, sweet green peppers I want to turn red, lemon cucumbers and regular green slicing cucumbers. The lids are closed down tight in the late afternoon and raised the next morning before the sun becomes warm enough to "cook" the veggies inside the cold frame.
Hope this gives you some ideas for your construction, Jordan. And thanks for being patient!
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