Cold Frame Gardening: Your Own Mini Greenhouse

What Is A Cold Frame?

A cold frame at its simplest is a bottomless box placed over garden beds to insulate plants from inclement weather. They are made of transparent panels that allow sunlight in, and often have a hinged top that can be opened and closed to modify the inside temperature of the cold frame.

Even though their name suggests that cold frames are for cold temperatures, they can actually be used in any season. They are most often used to protect growing plants from the cold, wind, and frost in spring and fall, however, cold frames can also be used in the summer to create microclimates for plants that are better suited for more mild zones than Utah’s.

DIY Cold Frame Vs. Prefab Cold Frame

Cold frames are a very popular DIY project because the idea behind them is pretty simple. A home gardener could use any number of at-hand materials to construct a cold frame: old windows, gardening cover, sheets of transparent plastic or glass, wood planks, bricks, and screen materials. All of these can be used to make a DIY cold frame, or other cover structures, like low-tunnels or hoop houses. 

If you’d like to learn more about hoop houses, check out our hoop house and low-tunnel blog post: https://www.pbsutah.org/blogs/modern-gardener/how-to-build-hoop-houses/

In Ashley Patterson’s garden, she opted to buy a pre-fabricated cold frame, rather than embarking on a DIY project. One reason for that is DIY cold frames are often bulky and difficult to store. The materials of Ashley’s prefab cold frame are light, easy to assemble, and easy to put back into the shed.

Ashley’s cold frames are manufactured by Juwel and are available in a few sizes and options. The sides and lids are made of lightweight, clear polycarbonate, with an aluminum frame, plastic brackets, and metal pins and screws. The polycarbonate is coated with a no-drip coating to prevent heavy condensation. 

With this information about the differences between DIY and prefab cold frames in your garden tool belt, let’s talk about what plants can be grown in a cold frame next!

What Grows Best In A Cold Frame?

Ok, you’re excited about extending your gardening season so that you can have fresh veggies to eat during wintertime, so let’s get into what veggies you could grow in a cold frame.

When it comes to choosing what plants to grow in a cold frame, the first consideration is the size of the plant. Crops that vine out or grow tall are not suitable for most cold frames, simply because they won’t fit in the cold frame. Keep the height of your cold frame in mind when planning your winter garden.

The hardiness of the plant is the next consideration. Cool-weather crops are what you’ll see most people using their cold frames to grow.

Here’s a short list of cool weather crops to get you inspired: 

These plants are hardy and will grow throughout a typical Utah winter under the protection of a cold frame. See this article for a detailed list of cold-hardy plants!

Although cold frames are most often used for half-hardy and hardy plants that thrive in cooler temperatures, don’t rule out using a cold frame to help warm-season crops too.

As an example of using a cold frame on warm-season crops, Ashley showed us how she used cold frames to extend the life of a basil plant and an eggplant that were adjacent to beds that she had been preparing for winter growing. These warm-season plants wouldn’t survive in a cold frame over winter, but because she had strategically planted them next to her winter beds, she was able to include them in her cold frame placement, protecting them from the early frost we had this year.

Ashley had other great tips for gardening in a cold frame, which we’ll share next.