About a half century before the term "hot-bed" was used to refer to a place or group which promoted the rapid development of some philosophy or phenomenon which was considered to be politically or socially subversive, a hot-bed was a simple, but ingenious, means by which to nurture tender plants early in the cool British spring. There were also some plants that did not require heat, but simply shelter from the harsher elements of the early or late weeks of the growing season. In these cases, cold frames proved the best solution. Both of these garden structures could be constructed for relatively modest costs, using simple materials. Thus, they could be found in a wide range of gardens during the Regency.
Of Regency hot-beds and cold frames . . .
There are records of various forms of protected agriculture dating back to the days of Ancient Rome, though neither hot-beds or cold frames have quite such a venerable history. Hot-beds are the oldest of the two garden structures, having been in use in Great Britain from at least the beginning of the seventeenth century. They were developed as a means by which gardeners could extend the growing season, usually for food-source crops such as fruits and vegetables, though plants with medicinal properties might also be nurtured in hot-beds.
The heat source for hot-beds was inexpensive, if malodorous; fresh manure. The best manure for the purpose was horse manure, preferably from horses regularly fed grain as well as hay. A layer of fresh stable manure mixed with straw would be laid down well below the rooting level of the plants, then covered with soil to a depth which would support the root systems of the plants to be nurtured in the hot-bed. Though it was not fully understood at the time, the microbial activity in the fermenting and decomposing manure and straw combination generated a significant amount of heat. Enough to sustain tender plants in the cold weeks of late winter and early spring. The depth of the manure and straw layer was determined by the length of time for which the heat was needed. For seedlings which were to be started in April, a manure depth of a foot to a foot and a half would be more than sufficient to provide the heat required until they could be transplanted into the open garden. However, if the seedlings were to be started in February or March, the layer of manure and straw would have to be two to three feet thick, in order to generate the heat needed for that longer period. Straw was an important component of the underlying layer in a hot-bed. If there was too little straw mixed in with the manure, there would be less heat generated for the plants above it.
Typically, most hot-beds were constructed with a border of wooden planks which was raised above ground level. In order to take advantage of any sunshine to supplement the heat generated by the manure, most hot-beds were oriented to be south-facing. The front of the hot-bed border was between eight to twelve inches high while the back could be as much fifteen to twenty inches high, to catch any incoming sunlight and reflect it back onto the plants in the bed. Hot-beds were usually four to six feet deep and could be anywhere from eight to twenty feet wide, though most tended to be between ten to fifteen feet in width. However, during the Regency, there were no standards for these garden structures and they could be made of any width, depth or height their builder wanted or needed.
Most Regency hot-beds were covered, at least after sunset, to trap the warmth around the plants, so it did not escape out into the cool of the night. Glass was not only expensive during the Regency, it was also heavily taxed. Certainly, glass was used by the wealthy in their glass forcing houses, but it was less likely to be used by those of more modest means for smaller garden structures like hot-beds. Many simple hot-beds were covered at night, or on very cool, cloudy days, by a sheet of cloth, often canvas, which would help hold the warmth in the bed. The gardener would have to remember to promptly pull that cloth cover back each morning in order to allow the sun to shine on the plants beneath.
However, there are suggestions in the records that at least a few hot-beds built by gardeners on a budget actually had covers of glass. These transparent covers were made from the frames of one or more discarded sash windows in which the glass was intact. Some householders actually removed windows from their homes and bricked up the openings after the passage of the window tax in 1745. A clever gardener and/or his carpenter, would be able to make a hot-bed frame of the correct size to be covered with one or a pair of old sash windows, instead of using a cloth cover. Glass covers would hold more heat in the hot-bed, but that could also be detrimental to the tender plants. The gardener would have to open the hot-bed cover for ventilation on those very sunny days when the heat inside the bed was too intense for the plants.
Cold frames came much latter to the realm of protected agriculture, in the early nineteenth century, quite possibly during the Regency. These garden structures were constructed in much the same way as were hot-beds, but they had no underlying layer of fresh manure and straw. Like hot-beds, they were usually placed to face south, with a border of wooden planks, the front height of the planks being lower than that of the back in order to capture the available sunlight and its attendant warmth. A few cold frames might be covered with glass, though that seems to be less common than with hot-beds. The majority of cold frames had a sturdy cloth cover which was pulled over the frame each night to hold in the warmth of the day and pulled back each morning to expose the tender plants to the sunshine.
Hot-beds were typically used most often in the spring to get a jump on the growing season by germinating seeds early so that seedlings would be ready to be transplanted into the open garden as soon as the weather permitted. On the other hand, cold frames could be used in both the spring and the autumn. In the spring, cold frames were often used to "harden off" plants which had been started in a forcing house or hot-bed. This was done in order to prepare those tenderly nurtured plants for the less stable conditions of fully unprotected growth in the outdoors before they were moved into the garden or field. In the autumn, cold frames could be used to plant one last crop of fruits and/or vegetables, giving them a better chance of surviving an early frost or two, thereby providing fresh produce as late as possible into the season. The rule of thumb with cold frames was that they could be used so long as daytime temperatures were 50º F or above. For those nights when there was a risk of the temperature falling below freezing, burlap bags stuffed with straw or dead leaves were placed over the cloth which covered the cold frame. This type of insulation was also occasionally used with hot-beds as well, should there be a severe cold snap in the early spring.
Hot-beds and cold frames were seldom used for flowers or other non-food plants. These garden structures took a certain amount of effort to construct and maintain, which was considered more appropriate for the production of food than for plants which were considered mainly decorative. Cooking herbs and medicinal plants might be given space in a hot-bed or cold frame, depending on the needs and preferences of the gardener. Many gardeners were very happy to have bee-hives located near their hot-beds and cold frames since they understood that their plants would flourish much better in proximity to the tiny industrious insects. In most cases, these protective garden structures were used to germinate seeds and nurture seedlings early in the growing season so that they could be set out in the garden or field as soon as possible. But in the fall, cold frames were sometimes used to allow crops to grow to maturity within their protective confines to provide one last round of fresh produce before the winter set in.
Dear Regency Authors, there are any number of ways in which a hot-bed or cold frame might have a place in a Regency story. The hero might find himself stranded in a remote country village in the fall, staying with a family who has offered him their hospitality until he can depart. Will he be pleased that there is a wide variety of fresh fruits and vegetables served at meals so late in the season, since the family has a cold frame in their garden? Or, does the heroine have something valuable which she must hide? The cold frame in the garden might be an ideal location. One would hope she would not choose to bury it in a hot-bed, considering the source of their heat. Perhaps the heroine, living in a cottage in the country, responsible for the support of her young siblings, has refurbished several old hot-beds in the garden where she forces many early fruits and vegetables to sell fresh, or to use in making preserves, which she also sells. Maybe her cottage is near the horse stud of the hero. Her young twin brothers, wanting to help, slip into the horse barns at the stud to collect fresh manure and straw for her hot-beds. What happens when they are nabbed by the hero?