If you’re the type of food gardener that wants to enjoy a 4-season harvest, you need learn about cold frames, ASAP. That is, if you’re not already using them.
Cold frames aren’t complicated, mystical or difficult to use. They are nothing more than a basic raised bed with an old door, window or other piece of glass placed on top. These humble boxes are true gardening wonders. They can extend your salad season by months. And, cold frames will allow you to sow some of your hardier seeds directly outdoors while spring is still chilly, freeing up your indoor space for starting other, more fragile crops like tomatoes. Which is great, because seedlings get a better start when they have real sun versus artificial light. Best of all, cold frames give you the ability to grow food year round, no matter what the weather is doing outside!
What can you sow and grow in a cold frame?
There are plenty of options for growing in a cold frame but these are some of the most popular:
- Lettuce – all kinds!
The veggies above are easy to grow and can be directly sown in cold frames, even in late winter. As your days get longer as spring nears, you can even grow and sow crops like bulb onions, tomatoes and potatoes in your cold frame. When the day comes that the cold frame is no longer needed, remove the top and move the cold frame “lid” to another bed or new location. Then you can start another round of seeds under the frame. In addition to direct sowing, you can also use a cold frame to sow hardy crops that are easily lifted and transplanted into rows, such as crops like onions and cabbage.
Options for Building Your Cold Frame
A cold frame can be made out of many things. You can build a simple wood box with a recycled window, door or even a shower door on top. You can use hay bales to make an enclosure and cover it with plastic. I’ve even seen cold frames built with bricks and concrete cinder blocks, using a piece of glass, plastic, or fiberglass on top. Pretty much any mixture of the above items will work, if you’re creative enough to make it all fit together nicely.
Your frames can be wildly different, however it is probably smart to try and make them of the same size, if possible. This way you can move the “tops” around from frame to frame as you need to in the early spring.
It’s best to build your cold frames in the sun, facing south if at all possible.
If you live in a colder climate (say north of Zone 6), you may want to add in extra insulation. Solar insulators are one way to add more warmth to your frame. This is done by placing black containers filled with water around the outside of your frame, and some gardeners like to place them inside the frame in the corners of the box. You can use pretty much any plastic container for this purpose – just paint it black. (I’ve heard of some people using wine bottles as well, though I have no practical experience with them myself.)
You can also insulate the sides of your cold frame with straw bales, piles of soil or mulch, or black garbage bags filled with leaves. On very cold days or nights, you can even use blankets for insulation!
Beware – Overheating
Cold frames will give your plants an extra shelter from the elements, such as ice, snow or cold winter winds. The soil inside the cold frame “heats up” in the sunshine, and will warm up much faster than regular ground soil. But if you’re not careful, your cold frame can overheat and fry your plants. It’s essential that your cold frame be opened a bit to allow excess heat to leave. You can do this by propping the top of your cold frame up with a stick on one side (like opening a lid on a hinged jewelry box). Be sure to fasten it carefully if winter winds are a problem.
On warmer winter days, or extremely sunny days (even if it is freezing outside), you should allow your cold frame to vent. If you can’t be around to open and close your frame, you can cover your frame with a light-blocking blanket during your absence.
Once you start using cold frames, you’ll be hooked, so beware. One little cold frame will multiply into several cold frames, and it’s easy to see why. Using cold frames in the garden allows you to enjoy a 4-season harvest and will bring spring to your garden weeks ahead of schedule.
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