Cold Frames 101

Note: this post orginally appeared in December of 2010. It was the first missive from Beth Gellman, AKA The Garden Coach, who still blogs for us. She'll have a new post next week. In the meanttime, enjoy this rerun, which has plenty of good advice for gardenders in any year.

I know what you're thinking. Did you just say COLD frame? It's logical to think about planting and harvesting when temperatures are still in the 90s, but doesn't it sound delightful to be thinking about seeing green in your garden in January or harvesting greens in early March?

When winter's approaching, and if you want to continue growing and harvesting vegetables, you had better have your cold frame ready. In fact, many cold-hardy vegetables will be ready to be transplanted or directly sown in the fall months.

So what is a cold frame? It's nothing more than four walls to trap heat and shelter plants, and a transparent lid that lets in the sun. You can make the walls from any sturdy material - plywood, concrete, even bales of hay. An old window works perfectly as a lid, but you can also use Plexiglas or plastic sheeting tacked to a frame.

How do I get started? I built my cold frame with the help of a friend last fall. There are many ways to approach it. I followed instructions I found in the book "Four - Season Harvest" by Eliot Coleman. Instead of using all new material for a lid, I went with what Eliot suggested which were used storm windows. I picked mine up at ReStore on Forest Park Parkway. Really neat place if you've never been there. It's an entire warehouse of used building materials.

Here is the illustration from Eliot's book and a picture from the book of a cold frame in use. I used the illustration to help get a feel for dimensions. Of course, I ended up building the frame to fit the size of the storm windows. The back side needs to be higher and it's best to place the frame facing south for maximum sunlight.

You can put the frame right on top of the ground or bury it slightly. I ended up mounting mine on top of some used landscape timbers. It's best if you can find wood that has been untreated with chemicals. Bad news if toxins leech into your plants (Eeeeewww!).

What about the soil? Prepare the soil to a depth of 12 to 18 inches, mixing compost, aged manure, peat moss or other forms of organic fertilizer with your existing soil to create a good fertile soil. Or, if your soil is quite poor you may want to start with a premixed commercial planting soil. Just add it right on top of the soil, as you would into a raised bed. You can also set potted plants in the frame as well, but I would make sure they are insulated with straw so they don't crack. I saw this demonstration on the web, not sure if this works with St. Louis winters. Experiment.

Added protection: if winter weather gets exceptionally cold, say down into the low twenties or teens, you will need to cover the cold frame with old burlap bags, old blankets, or any type of cloth material to provide added protection during the cold spell. Then once the weather has subsided, the covering material should be removed.

Warm weather: on a warm sunny day, during the fall, winter or early spring it will be necessary to open the window sash for ventilation. You can use a stick or wedge, or any similar material to prop it open.

Watering: you will have to experiment a little to determine how frequently to water your cold frame because the watering requirements will vary from day to day and season to season. Generally, during the winter season the cold frame will only need to be watered once a week. Or you can let Mother Nature do the job by opening the top of your cold frame on a rainy day.

Fertilizer: if the soil is prepared properly, there should be little or no need for feeding during the winter.

Best cold season veggies: leaf lettuce is undoubtedly the best crop to grow. It grows rapidly and abundantly in a cold frame. And, there's nothing like fresh, nutritious greens, picked from your own garden during cold winter weather. Spinach is also an excellent green to grow. Other crops that grow exceptional well in cold frames or hot beds are green onions, radishes, and chard, round or little finger carrots, endive and other greens. As you become more familiar with using your cold frame/hot bed, you will undoubtedly want experiment with other vegetables as well.

In addition to growing vegetables, a cold frame is an excellent place to start new seeds in springtime or to take cuttings in the fall and winter months of your favorite evergreen plants.

If you don't feel up to the challenge of building your own cold frame, specialty firms such as Johnny's Seeds offers a nice looking wood cold frame kit.

Beth Gellman is an EarthDance Farm Alumn and a landscape designer specializing in edible food gardens and community gardens. To contact The Garden Coach, please email Beth at gellmandesign@yahoo.com.