This section is from the book "How To Make A Flower Garden", by Wilhelm Miller. Also available from Amazon: The Well-Tended Perennial Garden: Planting and Pruning Techniques.
HOTBEDS are most excellent things for those who appreciate early vegetables. They are also useful for flowers, especially tender annuals, and enable the horticulturist, whether amateur or commercial, to hasten the growth of asters, pansies, and the like. In fact, a hotbed is a cheap and often the only available substitute for a greenhouse.
The size of a hotbed is determined by the requirements of the place; a convenient size is nine feet long, taking three sashes. An excavation three feet deep will be necessary. This should be boarded up completely from the bottom, the back rising two feet above the surface, the front eighteen inches. Cross-pieces four inches broad and an inch thick are let into the boards a sufficient depth to allow the edge of the boards to be even with the under surface of the sash when it is put on. A strip an inch wide and as thick as the sash, nailed along this, provides a tight frame for each sash, and renders ventilating easy.
Fresh horse manure is the material used to furnish the heat. A quantity sufficient for the purpose should be procured at one time. Small quantities procured at intervals will not suffice. After a few days the pile will begin to ferment, which fact is made evident by escaping steam. The pile should then be thoroughly forked over and formed into a new pile. In two or three days fermentation will again occur, and then the material should be put in the hotbed, treading it down evenly and firmly to a uniform depth of two and a half feet. It is better to mix decayed leaves in equal quantities with the manure, but this is not essential. If the leaves are used the work is hastened somewhat, as fermentation is not so active. The bed being made, put the sashes on the frame. When a thermometer, plunged into the manure, shows 90 degrees F., put in soil to the depth of five or six inches and firm it down. This should be a rich, well-prepared compost, one-third well-rotted barnyard manure and two-thirds fibrous loam.
Great care should be taken in watering. If too wet, the plants "damp off," or get weak and spindling; if too dry, they are likely to be lost altogether. Ventilation is a most important point; an hour's neglect may destroy the crop of seedlings. When the sun is shining, the temperature may be allowed to rise to 70 or 80 degrees; at other times, from 55 to 60 degrees is a proper temperature.
A market gardener's lay-out of glass (Near New York City).
Covering with mats and shutters is highly essential. If a cold night is coming, close up the frame early to store the heat, and put the covering on about an hour before sunset. Take it off in the morning from an hour to two hours after sunrise during cold weather. The sides and ends above-ground should be banked up with earth and six inches of manure to keep out cold in severe weather.
Of course, the young seedlings must be transplanted in the hotbed, and the cultivator must provide room enough for that purpose. A sash will cover fifty lettuce plants transplanted for forcing; it will cover 500 transplanted from the seed-bed. The latter number may be taken as a fair average for the general run of plants which a sash will cover after transplanting is accomplished. As sown in the seed-bed, before thinning or transplanting, a sash will cover about 5,000 seedlings. A sash will cover 500 radishes thinned out to grow to maturity.
In transplanting, be careful to do the work quickly and thoroughly, firming the plant well with the planting-stick. Do not allow the plants to be out of the ground a minute longer than is necessary. Water them well* after transplanting, and shade them with dampened sheets of paper for a few days until they have taken root. Tepid water, say 90 degrees F., can be used with benefit in watering plants in hotbeds, for the reason that the heat in the bed must be conserved. When the season's work is done, take out the manure and soil, which now has little value except, perhaps, to lighten heavier soils used for potting.