Protecting the Garden: Part Three

This is the last of a three-part series on ways to protect your garden. Part One covered cloches and row covers. Part Two covered hoop houses.

And now we come to cold frames. This is probably my favorite method for protecting the garden. Here’s why:

Inexpensive and effective

I’ve written about cold frames before. The are basically a mini-greenhouse that take in lots of heat from sunshine and the soil and keep it trapped overnight, or even for a couple days, to help plants survive freezing weather.

It takes a couple hour’s work to gather the materials and construct, so I put them on a par with hoop houses as far as the time you’ll need to invest. But for price and effectiveness, they can’t be beat. Read my previous articles on cold frames to see how successful they were.

Here are the materials you will need to make your cold frames:

• Wood to construct the frame
• A window to cover the frame
• Hinges to attach the window
• A stick to prop up the window when it gets warm

That’s it.

I found almost all the materials I needed on the boulevard during Spring Clean Up week: windows, wood and even a couple hinges. My total investment to construct three cold frames was the cost of four hinges.

Of course, you can use all new materials if you’re unable to find treasures that others have thrown out. Even purchasing new materials, a cold frame is still relatively inexpensive. The window is the most expensive part, so ask a window installer if he’ll let you salvage the old windows at his next job.

I like to make my cold frames just an inch or two narrower than my raised beds. If you don’t have raised beds, you can make them almost any size. The window size will probably determine the dimensions, but also keep in mind how difficult it will be to move the frame around.

The cold frame in late fall

Site the cold frame in your garden with the sloping window facing south to catch as much sunshine as possible.

Cold frames can protect your crops well into winter. They are lower to the ground and have less room for the air to cool, so they can retain even more heat than a hoop house. But that also means they aren’t good for tall plants like cabbage or broccoli. But they are perfect for low growing plants: leafy plants like collards and lettuce and root crops like radishes and beets.

Vegetables all winter long

You can harvest these vegetables all winter long, provided you can get to the plants and they aren’t covered with a lot of snow. Snow is a great insulator, so don’t remove the snow unless the forecast is for several sunny days so that the cold frame will heat up after you open it up to get to your plants. Even if it’s sunny, don’t open up the cold frame if temperatures are below 20°. Here in the upper Midwest, that means we leave the cold frames alone for the months of December through February. Just let the snow do it’s insulating job.

Will the brassicas and lettuce really survive our frigid winter temperatures? Yes. In theory. If everything aligns just right. I’ve had about a 50% success rate getting plants to survive all winter.

Here’s what I’ve learned to do to ensure the greatest success:

• Make sure there are no gaps at the bottom edge of the frame to allow cold air in.
• Insulate the inside of the box with 1.5″ Styrofoam insulation, cut to fit the box.
• Insulate on the outside with straw or leaves, making a pile around all the edges.
• Plant lettuce, collards and radishes in early September so that they have a chance to

As soon as the snow is gone or mostly gone, set your cold frames out in the garden to start warming up the soil. Start your cold tolerant plants (like brassicas) indoors in late January or early February. By mid-March they will be ready to harden off and transplant out into the cold frame.

When the soil temperature is 60°, plant peas and lettuce directly into the soil. Leave the window up during warm or sunny days and close it when the forecast is for anything below 30°.

Using a cold frame this way will give you a 6-8 week head start on your garden.

Putting it all together

All of the methods discussed in this three-part series will help you prolong your harvest and get more from the garden. Using a combination of all of these methods discussed will ensure that you get the most from your garden and have fresh vegetables for several months out of the year.

Pros and Cons

Using cold frames isn’t for everyone. Here are some of the pros and cons of a cold frame: