A full greenhouse is meant to be used for year-round growing, especially in colder climates. If your needs are simpler then a cold frame might be more appropriate. These are rather meant to protect plants from the harsh weather than to provide a year-round growing environment. Cold frames come in all sizes but many are small and meant for individual beds or a collection of plants. There are some major advantages and benefits to using cold frames instead of just leaving plants exposed.
Why should you use a cold frame?
- Extends the growing season – cold frames can be used a month or two before and after the traditional growing season. Doing this can lead to higher yields and better quality plants. It also gives you flexibility in your timing and planning. Being able to harvest fruits and vegetables out of season can save you a lot of money in the long run.
- Protection from the elements – obviously, a cold frame is meant to keep plants warmer than the natural environment, but they also protect from wind and harsh precipitation. Cold frames have the added bonus of protecting vulnerable sprouts and seedlings from animals who would like to snack on them, like rabbits and deer.
- Easy to use – most small cold frames can be assembled quickly and put to use immediately. They are not technically challenging to use or operate. They are also mobile and versatile so they can be reused on a wide variety of plants. Larger cold frames do take some assembly work but once they are up they are easier to maintain than heated greenhouses.
If any of the above apply to your growing goals then a cold frame may be right for you. Your natural climate and what you intend to plant also play a big role in choosing a cold frame versus a heated greenhouse.
When should you use a cold frame?
- When you need to protect plants during the winter. If you love the look of tropical plants in your beds but know they will be negatively affected by harsh winter elements, you can either bring them inside or put them in a cold frame. If you have a lot of plants, and minimal indoor space then a cold frame would definitely be preferable. A cold frame also allows more sunlight than even a sunny spot in your house, though you must take care not to give them too much since that may encourage active growth and we want to keep them dormant but alive.
- When you want to extend the growing season beyond the first frost. If you need or want to keep growing after the first frost hits then transferring plants to a cold frame can protect them at night and keep them thriving for several more weeks. Since the plants have been outdoors all year and have naturally acclimated to the cooling temperatures, they do not need to be covered during the day as long as the daytime temperatures stay above freezing.
- When you need to start seedlings early. In the same way that cold frames extend the end of the season, they can also provide an early start. Seeds can be started a few weeks early in a cold frame or up to six weeks earlier in a greenhouse or indoors. If you start them in a warmer environment they will need to be transplanted to the cold frame environment for a few weeks before being fully exposed to the outdoors.
- When young plants need to be hardened. If you have begun your planting indoors and need to move them outside you can either take plants outside and then inside for several hours every day or you can utilize a cold frame. Cold frames can actually heat up quite a bit so during the day they should be opened to allow the plants to acclimate and prevent overheating.
What kind of cold frame is best for me?
There are many different shapes and sizes of cold frames. If you have a single bed that needs some extra protection then a small pre-made frame can be used or you can create your own with a bit of framing and a glass or polycarbonate topper. This sort of temporary set up can be easily improvised and moved if necessary.
If you have started growing a line of plants like tomatoes and decide you would like to keep them growing past the first frost, a DIY hoop cold frame can be created in place with some rebar or stakes, PVC, and polycarbonate film. Simply place stakes on either side of the crop line and bend PVC over to create a hoop. Do this at intervals and then cover with the polycarbonate film to complete the protective covering. As long as the weather is warm enough, the film should be rolled back during the day to prevent overheating.
For starting seeds early or having a station to harden seedlings and new plants, you may want a small box cold frame. If you think you will need it multiple years in a row then you may want to have one semi-permanently installed outside of your house or greenhouse.
Serious growers may want a larger cold frame, at least large enough to stand up in or maybe even the size of a full greenhouse. If you are not handy then a kit would be advisable. For the handymen among you though, a simple large cold frame can be built with some extra lumber and some cover material.
For ideas about where to start with installing a cold frame in your garden do a quick search for “cold frame” here on greenhouseemporium.com. There are several models of different sizes and functions. You might either find these to be right for your use or at least use them as a starting point for building your own cold frame.