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Hot cold

Cold frames, hotbeds provide a way to grow plants out of season

The battle of weather versus gardener is in full swing. Weather has the upper hand as temperatures plunge to well below freezing each evening.

Growing out of season is always a challenge. Temperature is the most limiting factor and one of the more difficult to overcome. Heat is hard to supply in the right quantities at the right times to help plants thrive through the winter.

A greenhouse works well, but it can be expensive to build and operate. That's why most avid gardeners who practice their hobby in cold weather usually build hotbeds or cold frames. They are much less costly.

Replicas of these devices that operated more than 250 years ago were rebuilt in Colonial Williamsburg. They are used to start vegetables for gardens today.

My first introduction to hotbeds and cold frames came from immigrant gardeners in my hometown. They built them to support their individual vegetable gardens that would flourish with tomatoes, peppers and other favorite Italian, Greek and Slavic favorites. When I needed tomatoe starts for my own garden, I would visit their's and purchase some of their surplus plants.

These garden artisans would carefully lift the old window panes that made the top of their frames. The image of their picking up their watering cans and soaking the plants and then pulling them up in clumps and wrapping them in brown paper are still clear in my mind. Parting with a few cents, I would then be on my way to plant them in my own garden.

Eventually I built my own and used it to start plants. Following their advice and an antiquated gardening book that my grandfather had, I made a serviceable cold frame that I used for several years.

By definition, the growing device I built was a cold frame. This protected plant beds and grew plants in an environment that had no artificial heat. The old wooden-framed window on the top collected sunlight during the day and, I hoped, kept the plants a little warmer at night.

The temperature difference inside of the frame was usually only five to 10 degrees higher than the outside. On cold nights, I covered the frame with a blanket to reduce the heat loss, but that didn't make the plants any warmer.

It soon became evident that I needed to add extra heat to get my plants off to a better start. Out came the old garden book for more instructions. The conversion from cold frame to hotbed was simple. A hotbed is nothing more than a heated cold frame. It is, essentially, a miniature greenhouse and provides a heated environment for growing plants at minimal expense.

I was on a budget and had to use what I had on hand, and my reference text was somewhat antiquated, so the recipe to heat the device would be unconventional by today's standards.

The paraphrased recipe was as follows: Dig a pit three feet deep under the cold frame. Fill the pit with fresh horse manure. Add a 6-inch layer of sand or soil on top of the manure. Plant the seeds in the soil or place planted pots in the frame and then cover with the glazing; ventilate to control the temperature as needed.

This was long before the days of endless disclaimers and repudiations. Nowhere in the text was there a warning about the smell or the discomfort of shoveling manure in and out of the hole. Likewise, there were only vague instructions about growing the plants. You were at the mercy of the horse manure contents because as it decomposed it warmed the bed and kept the plants growing. If it decomposed faster, your hotbed was warmer; if it was slower, the bed stayed colder.

Most gardeners now opt for a less odoriferous method of heating. In my classes, I often offer impassioned instructions of how this method of heating is very good because it reduces our dependence on imported oil and on fossil fuels. It is also a significant method of recycling. But I'm afraid these portions of my lectures are ignored. I don't think that even one of the thousands of students I have taught has have tried this method.

Building and operating one of these structures is far less costly than a greenhouse. Many people use recycled materials with only a small outlay for hardware. Unless you want to stand and walk among your plants and grow them year round, hotbeds make much better sense than a greenhouse.

The structural design is simple. Build a rectangular box with the back higher than the front and cover it with a transparent roof. Whatever the size, make certain the slope from back to front is at least 1 inch per foot. Every other variation on this basic plan only increases the size or the complexity of the bed, but does not necessarily make it any more functional.

Use glass, fiberglass, acrylic plastics, double-walled greenhouse plastic or clear polyethylene to cover the frame for the glazing. Fix the frames on hinges or hooks to prevent them from blowing away during strong winds.

Make the sides of the structures out of wood, brick or concrete. Concrete or brick are more permanent and are more costly than wood. Wood is the easiest to fabricate and will last longer if you use pressure-treated lumber. An alternative is to treat the wood with a preservative that is not toxic to plants.

Paint the inside of the frame with white paint to increase the light reflection. Line the frame with water-resistant foam insulation. This holds the heat and greatly increases the heat efficiency, making it easier to grow plants.

If the winter cold has you feeling the blues, get in a little green by building a hotbed or cold frame. Use it to start plants earlier in the spring and protect plants in the fall. They also are useful to over-winter semi-hardy plants, harden transplants, dry fruits, vegetables and flowers or force bulbs. Best of all, they are easy to build and operate and they provide hours of enjoyment for any gardener.