A hotbed can also be heated by running steam pipes through the ground, but unless you happen to be where exhaust steam could be used, this method is not economical except for big houses. The care and expense of a separate steam plant would be too great to pay, unless for growing winter vegetables for market or flower culture. If you go into that on a scale large enough to pay, new problems at once demand solution.
Vegetables under glass have kept pace with other crops. Within fifteen miles of Boston are millions of square feet of glass devoted to vegetables, chiefly lettuce. There are more than five million feet in the United States used for other crops. Ordinarily, under favorable conditions, glass devoted to this work will yield an average of fifty cents per year per square foot.
About the lowest estimate of cost per sash is five dollars; this amount includes the cost of one fourth of the frame and covers. There are usually four sashes to one frame. A well-made mortised plank frame costs four to six dollars. A sash, unglazed, costs from one to two dollars. Glazing costs seventy-five cents. Mats and shutters cost from fifty cents to two dollars per sash, depending upon the material used. Double thick glass pays better in the end as being less liable to breakage. These prices vary greatly, however.
The following sample estimate by a gardener is for a market garden of one acre, in which it is desired to grow a general line of vegetables. It supposes that half of the acre is to be set with plants from hotbeds.
One eighth acre to early cauliflower and cabbage, about 2000 plants, if transplanted, would require two 6 X 12 frames, from two hundred to two hundred and fifty plants being grown under each sash.
These frames may be used again for tomato plants for the same area, using about 450 plants. This will allow a sash for every 55 plants.
One frame should be in use at the same time for eggplants and peppers, two sashes of each, growing fifty transplanted plants under each sash.
Two frames will be required for cucumbers, melons, and early squashes; for extra early lettuce, an estimate of sixty to seventy heads should be made to a sash. It is assumed that celery and late cabbages are to be started in seed beds in the open.
In the fashionable suburbs of Boston "one hotbed 3 X 6 feet was used in which to start the seeds of early vegetables. Plantings were made in the open ground as soon as the weather permitted, and were continued at intervals throughout the season whenever there was a vacant spot in the garden. The following varieties of vegetables, mostly five-and ten-cent packets, were planted: Pole and wax beans, beets, kale, cabbage, carrots, cauliflower, celery, corn, cucumbers, corn salad, endive, eggplant, kohlrabi, lettuce, muskmelon, onions, peppers, peas, salsify, radish, spinach, squash, tomatoes, turnips, rutabagas, escarole, chives, shallot, parsley, sweet and Irish potatoes, and nearly a dozen different kinds of sweet herbs."
"In the larger garden, tomatoes followed peas, turnips the wax beans, early lettuce for fall use took the place of Refugee beans. Corn salad succeeded lettuce."