Cold frames are wonderful places to produce transplants to set out in your garden. They are most often made of wood, but not necessarily. The one you see in the photo is made from 1½” thick pine that has been primed and painted. It is 3’x6’ because that’s the size of the piece of glass I had available to make the top. The new one I’ve built is 4’x8’ and has four 2’x4’ lids that are easier to manage. The design I followed is in Eliot Coleman’s Four Season Harvest. My cold frames stay in one place and are part of my garden design. I painted them white because it looks nice and to keep anyone from stumbling into them, particularly in the evening as the sun is fading. Set on top of 3½” thick solid cement blocks so they don’t get waterlogged in the early spring, my cold frames are “landmarks” in my garden.
Coleman has a new design that is shown in The Four Season Farm Gardener’s Cookbook. It is for a 4’x4’ model that he suggests moving around the garden as needed. In that case it is used to cover a whole crop, not necessarily different varieties of seedlings for transplanting. If you had a small movable cold frame you could have it in one bed for the year and move it once each year with the rotation of crops, or you could move it around every few weeks. If you did that, rather than have a whole frame to move, you might want to have wide boards that hold together with hooks and eyes. They would be easy to move and, when not in use, the boards would stack in one pile. The tops can be made from wood frames covered with plastic.
I use movable season extension made with hoops and plastic for cold weather greens, but for growing transplants, I prefer my wooden cold frames that have an established home in the garden. With the tops off for much of the year, there is no build-up of pests. Whenever I plant a new batch of seeds, I add compost to keep the fertility up and to give the seedlings the probiotics they need for a good start. The planting season begins in January or February, with the first round of seeds being onions, the cabbage family, and sugar snap peas, all for transplanting. Whatever had been in there before, needs to be out by that time, so this is not the place for winter harvested greens, which would still be going strong. Lettuce, planted in September and held into the winter, would be past its prime by that time. If roots — carrots, beets, and parsnips — had been planted there earlier, they would all have to be harvested by the time the first seeds go in after the New Year. These root crops do not need the protection of a cold frame in my Zone 7 climate.
By late winter, and the cool season crops have come up, and the lid can be opened. By the time these seedlings are ready to be planted in the garden, the top would have already been off the cold frame for an extended time. Next would come the warm weather crops, such as tomatoes and peppers. I start these seeds in the ground in the cold frame about a month before my last expected frost. Of course, the covers for the cold frames would need to be back on. I like to have two cold frames in operation so that I can treat them differently—cover on for the warm weather plants and cover off for lingering cool weather crops. Otherwise, I would transplant the cool weather crops into wooden flats, before adding warm weather crops to the cold frame, if they still needed some time before transplanting in the garden.
It is after the warm weather crops have been transplanted out, that cold frames might fall into disuse. I want to encourage you to keep planting. As room opens up in your garden throughout the summer, you can fill it with transplants from the cold frame. By then, the covers would have been put away for the summer and you are only using it as a dedicated space for starting seeds. If my summer seedlings can benefit from some shade, I will put plastic hoops over the cold frame and attach a piece of shade cloth with plastic clips that will hold shade cloth or plastic sheeting to round pipes.
You can find more information about getting the most out of your cold frame at Homeplace Earth. With some experience, you can develop a rotation for your cold frame, just as you would have a rotation for your garden beds, so you know what to expect and how many cold frames you might need. With a little planning, you can have a never ending supply of transplants.
Learn more about Cindy Conner and what she’s up to at www.HomeplaceEarth.wordpress.com.