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When I first started experimenting with season extension, I discovered that a cold frame is an invaluable tool in a vegetable garden. Our cold frames allow us to jump-start the spring harvest months before most gardeners begin to sow seeds and stretch our harvest throughout winter. If you want tips on how to garden with a cold frame, read on. Here’s an excerpt on cold frames from my award-winning book, The Year-Round Vegetable Gardener.
Learn how to garden with a cold frame:
If I could pick only one season-extending device, it would be a cold frame. Incredibly useful, a cold frame is the key to increasing the production in your garden from three seasons to year-round. The more I garden in my cold frames, the more cold frames I want to have! It’s such an invigorating feeling to lift the lid of a frame in the middle of January and find it filled with fresh, leafy greens, crisp carrots, and aromatic herbs, just waiting to be harvested. At its most basic, a cold frame is simply a box with a clear or translucent top. Its purpose is to trap solar energy and provide protection from the elements — cold temperatures, excessive rain, wind, and snow. The back of the box is typically taller than the front (usually by 3 to 6 inches), which lets the top of the cold frame (often called the light, sash, or glazing) sit at an angle. This slope allows maximum sunlight to enter the structure and will help it shed rain and snow.
Cold frames are easy and inexpensive to build (even for a nonhandy person like me) and can be constructed from simple, often recycled materials: use scrap wood, straw bales, bricks, and old windows. My husband, Dany, built my cold frames out of simply cut pieces of lumber and a few sheets of Lexan.
A cold frame can be constructed as a portable device, moved from bed to bed whenever a bit of protection is needed. It can also be a permanent part of the garden, multitasking as a seeding bed, a spot for hardening off young seedlings, getting extra-early crops in the ground at a time when the unprotected garden is still frozen, creating a microclimate for heat-loving crops like peppers and eggplants, and extending the harvest of cool and cold-weather vegetables into the depths of winter.
When you garden with a cold frame you move your plot the equivalent of about one gardening zone to the south. My south-facing, slightly sloped vegetable patch is located in Zone 5b/6. Growing vegetables year-round in unprotected garden beds is still rather limited in that zone, but with our simple cold frames, we’re able to create the conditions of Zone 7, extending both our season and the variety of crops we can grow.
A cold frame can be used alone or in conjunction with other season-extending devices, such as a greenhouse. Adding several cold frames to the interior of an unheated greenhouse will enable you to garden as if you were two zones to the south, further increasing the variety of crops you can cultivate in winter.
Types of Cold Frames:
There are three main types of cold frames — portable, permanent, and temporary. They can be built from a wide assortment of materials such as wood, aluminum, polycarbonate, cinder blocks, and straw.
A portable cold frame is usually smaller and more lightweight than a permanent structure is. Kits for portable cold frames, which are available through catalogs and garden centers, often have frames constructed from aluminum with polycarbonate tops and sides. This allows for easy transporting from bed to bed. They’re ideal for protecting spring and fall veggies from light frosts or a brief cold spell but aren’t generally insulated enough to protect cold-season greens over the winter. They can, however, still be used to insulate root crops like carrots and parsnips when filled with a thick layer of leaves. In mild areas, however, a portable frame may be all you need to successfully winter-over cold-hardy vegetables. Many store-bought kits are easy to assemble and take apart, so you can store them during the summer months. You can also make your own portable cold frame from wood and clear plastic or polycarbonate.
Most of our cold frames are permanent, in-ground structures that provide us with insulated and sheltered spots for growing a variety of crops throughout the year. Because they cannot be moved, they must be placed in the right location to ensure maximum solar exposure. Unlike a portable cold frame, the box of a permanent structure is typically constructed from a solid material like wood or cinder blocks and the only light that reaches the plants enters the structure from the top. We like to sink ours into the ground because that offers better insulation and helps protect the crops.
A temporary cold frame is an easy way to experiment with cold-frame culture, without actually going to the trouble of building a permanent structure. I use temporary frames to cover some of our taller cold-tolerant vegetables like kale and leeks. With just a few straw bales and an old window or a sheet of rigid plastic, you can quickly construct a temporary cold frame. Come spring, use the straw as mulch in the garden beds or along pathways.
For more on cold frame gardening, check out this video tutorial.
Excerpted from The Year-Round Vegetable Gardener © by Niki Jabbour. Used with permission from Storey Publishing.
Do you want to learn about how to garden with a cold frame? For more information on building a frame, caring for cold frame crops, and harvesting all year long, check out my book The Year-Round Vegetable Gardener.
Other books by the Savvy Gardening experts:
- Container Garden Complete by Jessica Walliser
- Attracting Beneficial Bugs to Your Garden by Jessica Walliser (Winner of the American Horticultural Society Book Award)
- Good Bug, Bad Bug by Jessica Walliser
- Raised Bed Revolution by Tara Nolan
- Groundbreaking Food Gardens by Niki Jabbour
- Veggie Garden Remix by Niki Jabbour
- And both Jessica and Tara contributed to the new book, Gardening Complete