Quick and Easy Coldframes

Panel bed vented LAHWe all want to plant our veggie gardens now, but winter hasn’t quite let go of the Rockies. While last week was in the 60s, it’s snowing as I write this, and snow and frost are distinct possibilities for several more weeks.

This is the time of year when we suffer most from greenhouse envy. Yet, for a minimal amount of money, time and effort, you can build a mini-greenhouse right over your garden beds. Here’s how I went about it.

If your garden beds have enclosed sides, it’s easy to convert them into a coldframe. Corrugated fiberglass panels are available that are specifically made for greenhouse use, and they’re not terribly expensive. I purchased several 8-foot lengths, cut them into 4-foot pieces, and simply laid them across my boxed beds. Add some weights to keep them from blowing away, and you have instant weather protection.

When driving rain, snow or hail threaten, your seedlings are safely covered. If weather turns particularly cold, insulate your covers. A thick layer of straw works well for this. Make sure to seal off the sides—I use additional straw to keep cold winds from sneaking under the covers and chilling my baby plants. Or,  you can cover the entire bed from end to end, so there are no open sides.

On sunny days, plants can quickly bake under plastic, so be sure to vent your covers if the sun is shining. You can simply slide them apart, or just raise one end (see photo). The hot air rises and cool air flows in to replace it.

As your plants grow, you can raise the covers by adding additional supports underneath.

I find these in-bed coldframes to be the perfect place for early lettuce. I have set out transplants (grown indoors under lights) on March 1 and harvested leaves from mid-April on. (Many leaf lettuce varieties are hardy to about 10 degrees!)

I’ve used these covers on most of my crops, from cabbage to zucchini, spinach to beets. Just remember to water, as rain won’t reach your plants.

To add some additional warmth to your coldframes, convert them into hotbeds. Decomposing plants release heat as they rot. You may have the steam rising from a well-built compost pile. We can take advantage of this heat by digging down and layering compostable materials under the surface of the soil. Partially rotted compost works great. Cover with a fluffy layer of dirt, then plant the seedlings on top. The decomposition going on underneath will keep your transplants’ roots toasty, and provide you with an earlier harvest.

You can also use plastic covers to preheat your soil, so the tomatoes, squash and beans you plant later (once frost is unlikely) get off to a good start. Place the panels over your beds a couple of weeks before you set out your transplants.

We may not have the huge greenhouse we’re dreaming of, but with a little ingenuity and a bit of plastic, we can start our gardens now.

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