Cold Frames - many uses

Cold frames are a great tool for vegetable gardening. They're a great tool because they have so many uses throughout the season, and can be used in combination with other resources to provide a year round harvest of fresh vegetables.

If you've considered a regular greenhouse or a hoop greenhouse or a tunnel of some sort, or even a system of row covers, then you'll be able to appreciate the usefulness of this handy vegetable gardening resource.

Let's look at the basic design, and then how we might integrate this resource into our vegetable gardening. Cold frames can be used at the start, throughout the growing season, and into an extended harvest season.

Design of Cold Frames

The basic design of any frame is to provide a rigid structure that protects plants from wind and weather, and provides an angled transparent or translucent top that let's in light. Some frames use wood for the sides, and others use glass or another clear material.

The enclosure has to be highly weather resistant, yet capable of letting in sunlight to help germinate seeds, grow seedlings, and provide a protected area for young and small plants.

The key to using a frame is to let in natural light from outdoors, instead of using grow lights or fluorescent lighting indoors. Seedlings respond so much better with natural light. Without it, they tend to get leggy and can't stand up on their own.

Homemade frames are generally made of wood on the sides, with a glass or (rigid or fabric) plastic top. Commercial frames typically use glass or rigid plastic for the top and sides, with aluminum framing to provide structural support.

euro-style unit

This style would be useful to face the tops east and west, to allow gathering morning and late afternoon light. Or, it could be faced north and south to capture good light from the south during the midday, while allowing access from the north side. This might be more convenient for some situations.

Uses of Cold Frames

The traditional use of cold frames is to start seedlings. The frame provides a miniature greenhouse within which seedlings can enjoy warmth, and still be protected from wind, rain, hail and critters.

Again, most importantly, the frame has a clear or translucent top that allows the seedlings to be greeted by natural sunlight, and this serves their needs much better than any artificial light you could ever provide.

Cold frames are also very useful for hardening off seedlings. This is the process of letting seedlings get accustomed to outdoor conditions a little bit each day until after a week or so, they are ready to be transplanted outdoors where they will spend their lives producing vegetables for you and your family.

double lid unit

Another use of frames is to protect new transplants until they get their "sea legs" under them. Young and tender seedlings can be beat up pretty bad by wind, storms and strong rain. Using a frame that has no bottom on it will allow you to selectively cover plants that may require it from time to time.

Yet another use of cold frames is to help extend the season for low growing cold hardy vegetables. Like a greenhouse, use of a frame can help you start off the season earlier and call it quits later. In some cases, you might be able to stretch the season two months in either direction - that's significant.

The commercially made double lid unit on the left uses a standard "propping" method to vent the interior during periods of intense sunshine. For high wind areas, you'd want to secure the lids with a strap or weight.

Cold frames can also be used as miniature greenhouses to grow lettuce and salad greens all year long in milder climates, although this is only practicable for low growing plants. The big drawback of trying to do this is regulating the temperature of such a small space. Smaller spaces are much less forgiving and will have tremendous temperature swings. They get hot quick, and with one opening of the top, whoosh, your warm air literally goes out the window.

In harsher winter climates, you can grow winter vegetables without adding any heat. You can do this if your frame is sitting inside a grow tunnel or greenhouse.

Here is how it works. The larger structure protects against winter winds and harsh cold, and collects energy during the day. When the temperatures drop to 10 degree outside at night, the inside temperatures might remain in the 30s, while inside your cold frames will likely be in the 40s.

The frames capture ground heat and keep it trapped inside for a longer period, thus adding another layer of insulation for your plants. You can't grow summer vegetables this way, but many winter vegetables and cold tolerant crops will do just fine inside the frame well into winter.

Other Considerations

Here is a list of other considerations when selecting or building cold frames for any of the purposes mentioned above.

• Small spaces heat up and cool down quickly, so be mindful to manually vent the frames, or install an automatic vent.

• Large frames can be a permanent part of your greenhouse. Just mount the frame on the soil and plant directly in the soil.

• Frames should be easy to take down for transport or small enough to transport by one person. Handles are helpful.

• Clear or translucent top and sides give better light for plants and make the frame more effective.

• Protect the top from hail damage if that is common in your area. A thin piece of plywood is hail proof except for the largest of hailstones.

• Seed mats or water bed heaters (if set up properly) can be used to provide heat inside the frames for tender seedlings that are set out in the sun during the winter. This will help keep nighttime temperatures from going too low. Be sure to cover the frame at night with an old comforter, sleeping bag or similar insulating material.

• Making multiple uses of your frames will increase their cost-effectiveness, so plan to make them work for you year round.

Think of ways to incorporate cold frames into your vegetable gardening as a value resource for enhanced effectiveness, higher yields and an extended season.

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