This is an ambitious cold frame. It measures 13 1/2 feet by 9 1/2 feet. It features a network of boards which hold up the glass and also allow the gardener access to the plants without stepping onto the dirt. This prevents compaction of the soil.
This cold frame is also permanent, not portable. This violates a rule of cultivation that tells you to rotate crops, and there is good reason for this rule. To compensate, I have tried deep turning of the soil at the end of the growing season (early summer), and I've also tried taking some soil out and bringing in soil from other parts of the garden. I am on my fourth year with this cold frame, and so far, I've harvested a great quantity of delicious spinach from it, so I guess it works. (I tried several varieties of lettuce one year, but the spinach was higher quality and more productive.)
Procedures
The first step in building any cold frame is to acquire the glass. The dimensions of your glass dictate the dimensions of your cold frame. In this example, six standard 36 inch sliding glass doors serve as the glass cover. The doors are 78 inches tall.
The second step is to acquire the wood. The 2 X 6 boards in this cold frame began their lives as planks in a deck, and they came to me through my local building materials recycler, EcoStores Nebraska. I was lucky to get these boards because they had already been treated to retard moisture soaking into them, and they had also aged. I found several perfectly straight boards in the batch, two of them were 16 feet long!
Next, mark out a rectangle on the ground and make sure your corners are square. At the corners, sink corner posts into the ground. I used short, treated 4 X 4 boards and buried them 24 inches deep with 6 inches extending above the ground. Next, clamp the ends of the long boards to the posts and adjust them so that the two long boards are parallel with each other.
Next, dig a 16 inch hole at the mid point of the two long boards and bolt a length of scrap 2 X 8 to the boards so the 2 X 8 goes down into the hole. Fill in the hole and tap down the dirt. Next, drill holes through the corner posts and the ends of the long boards and bolt the boards to the posts.
The long boards are now secure at the ends and the middle, and they won't twist with age. Finally, secure the short boards to the corner posts, lining them up with the long boards to form a consistent top. Your rectangle is now complete. A little dirt shoveled around the edges will seal out cold drafts from the growing plants inside.
For the network of boards supporting the glass, I chose to keep all the boards flush with the top of the exterior rectangle. To accomplish this, I had to create a central cross piece with cuts in the board to support radiating boards to hold up the individual glass doors. If you get this far, the problem will be obvious, and you can implement the solution that matches your skill, tools, ambition, and materials. You're creating a flat surface over which your glass doors can easily slide into place and over which you can move freely. When you're done, you'll have 6 small gardens, each the size of a 36 inch sliding glass door.
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