Whether to get an early start on the garden or for raising plants for field crops, a hotbed is all but indispensable. In making a hotbed what we seek to do is to imitate Nature at her best, so get the best soil and the sunniest spot you can find.
In all hotbeds the underlying principle is the same: They are right-angled boxes covered with glass panes set in movable frames and placed over heated excavations. The bed may be of any size or shape, but the standard one is six feet wide, since the stock glass frames are usually six feet long by three feet wide. You can have any length needed to supply your requirements. "Tomato Culture," by A. J. Root, tells us that the cheapest plan is to get some old planks, broken brickbats or stone, and piece together a box-like affair in proper shape: to provide drainage, the front should be at least ten inches above the ground and the rear fourteen inches. A hotbed knocked together in this way is all right to start with, if you cannot do any better, but will last only two or three seasons. For a permanent bed, probably the best way is to make cement walls extending to the bottom of the manure. The bed ought to face south or southeast and be well protected on the north. It should be banked all around with earth or straw to keep out the cold, and mats or shutters should be provided for extra cold weather. The best material for heating the bed and the most easily obtained, is fresh horse manure in which there is a quantity of straw or litter. This will give out a slow, moist heat and will not burn out before the crops or the plants mature. Get all the manure you need at one time. Pile it in a dry place and let it ferment; every few days work the pile over thoroughly with a dung fork; sometimes two turnings of the manure are enough, but it is better to let it stand and heat three or four times.
"You can make a hotbed also on top of the ground without any excavation. Spread a layer of manure evenly one foot in depth and large enough to extend around the frame three feet each way. Pack this down well, especially around the edge, put on a second and third layer until you have a well-trodden and compact bed of manure at least two and one half feet in depth. Place the frame in the center of this bed and press it down well." A two-inch layer of decayed leaves, cut straw, or corn fodder, spread over the manure in the frame and well packed down, will help to retain the heat. Ventilate the bed every day to allow steam and ammonia fumes to pass off.
"The soil inside should be equal parts of garden loam and well-rotted barnyard manure. Tramp well the first layer of three inches. To make it entirely safe for the plant seeds in the hotbed, add another layer of the same depth. Use no water with garden loam and manure if you can possibly help it."
"Before sowing any seeds put a thermometer in the bed three inches deep in the soil. If it runs over 80 degrees Fahrenheit, do not sow. If below 55 degrees it is too cold; you will have to fork it over and add more manure. If the bed gets too hot, you can ventilate it with a sharp stick by thrusting it down into the soil."
Another way that the old gardeners have to make a hot bed is with fire. On a large scale this is cheaper, though more complicated than the fermentation of manure. In making this kind choose your location and build the frames as before. "Cut a trench with a slight taper from the east end of the plot to the end of the hotbed, and on under the ground to about four feet beyond the end of the bed. This taper to the outlet will create a draught and so keep a better fire. Arch this over with vitrified tile. The furnace end where the fire is should be about six feet away from the bed. When the trenches are completed, cover over with the dirt that was taken out of them. Two such trenches under the frames will make a good hotbed. Anyone can do this sort of work."
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."
"The spinach was followed by cabbage, while turnips, beets, carrots, celery, and spinach gave a second crop in the plot occupied by Gardus peas and Emperor William beans."
"Winter radishes came after telephone peas, Paris Golden celery was planted in between the hills of Stowell's blanching. The plot of early corn was sown to turnips. The hotbed was used during the late fall and winter to store some of the hardy vegetables, and the latter part of October there was placed in it some endive, escarole, celeriac, and the remaining space was filled up by transplanting leeks, chives, and parsley." (Bailey, "Principles of Vegetable Gardening," page 38.)
"If spinach is grown in frames, the sash used for one of the late crops above may be used through the following winter.
"This, like the last case, makes a total of five frames, the cost, depending on make and material, from one to five dollars; twenty sash and covers, at, say, $2.75, $55; manure at market price, calculating at least three or four loads per frame. This is a liberal estimate of space, and should allow for all ordinary loss of plants, and for discarding the weak and inferior ones. It supposes that most or all of the plants are to be transplanted once or more in the frames. Many gardeners have less equipment of glass." (Same, pages 49-50 )
Growing vegetables under glass gives smaller returns than flowers; as, for instance, a head of lettuce brings much less than a plant of carnations, and suffers more from the competition of southern crops. Nevertheless, the greenhouse-grown vegetables have come into prominence lately because they can be raised in houses that are not good enough for flowers. Lettuce and tomatoes are the principal crops; some growers raise thousands of dollars' worth each year. The greenhouse is also used for forcing plants which are afterwards transplanted to the open air. This develops them at a time when they could not grow outdoors and gives them such a start that they are very early on the market, thereby realizing the highest prices.
"Nearness to market is the most important feature in a greenhouse. In large cities, manure, which is the chief fertilizer, can be had in most cases for the hauling. The short haul is an important item, and, most important of all, the gardener who is near the market can take advantage of high prices, if the grower is near enough to the city to make two or three trips; in such a fluctuating market as New York, it is to his advantage."
Some kind of a greenhouse is necessary, but one large enough to produce a living would cost a very large sum. Vegetable raising under glass has been made profitable in special localities where nearly the whole community gives its time to building up the industry, but complete success can be attained only by having absolute control of all the conditions entering into production, and giving assiduous and undivided attention to detail.
Leonard Barron, in the Garden Magazine, says: "The best type of greenhouse for all-round purposes is unquestionably what is known as the even span—that is, a house in which the roof is in the form of an inverted V, so as to be exposed as much as possible to sunlight, and having the ridge-pole in the center. All other types of houses are modifications from the simplest form, and are designed in some way or other to fit some special requirements. These requirements may be: the cultural necessities for some particular crop; a desire to have the atmospheric conditions inside more or less abnormal at given seasons (as in a forcing house); or an adaptation to some peculiarity of the situation, as when a greenhouse is built as an adjunct to other buildings."
"It is plain common sense that the ideal greenhouse is one in which the light is most nearly that which exists outside, and in which the heat is as evenly distributed. It is practical experience that a structure with as few angles and turns m it as possible and with a minimum of woodwork in its superstructure, best answers these conditions.... Greenhouse building has developed into a special industry, and the modern American greenhouse is the highest type of construction. It is built with as careful calculation to its situation and its requirements as is the country dwellinghouse. Such a thing naturally is not cheap."
"The low-priced 'cheap greenhouse' is a makeshift of some sort. Perhaps its roof is constructed of hotbed sash, a perfectly feasible method of construction, which for ordinary, commonplace gardening will answer admirably. Or, its foundation is merely the plain earth. Such a building does admirably in the summer time, and even in the late spring and early autumn; but woe betide the enthusiastic amateur in winter, who, being possessed of one of these light greenhouse structures, has indulged in a few costly, exotic plants. They will be frozen, to a certainty! It is economy to pay a fair price in the beginning to secure a properly built greenhouse that will withstand the trials of winter."
"If iron frame is used instead of wood there is greater durability, and the structure being more slender, will admit more light, but the cost will be increased."
"It makes very little difference in cost what shape of house is to be erected. The cost per lineal foot for an even span is practically the same as for a lean-to of the same length and width. In the lean-to, in order to get the sufficient bench and walk space inside, it is necessary to carry the roof to a point much higher than in the even span. The extra framework and material for the roof cost a good deal, yet add practically nothing to the efficiency of the house."
"Heating of greenhouses is best done by hot water, and in a small house the pipes may well be connected with the heating system used for the dwelling, if the greenhouse and the home are within any sort of reasonable distance from each other. For large houses, or ranges of several houses together, the independent heating plant is necessary. Steam is used for heating by commercial florists, but it is economical only on a large scale."
"As a uniform temperature must be maintained in the house, the fires, where steam is used, need watching continuously during cold weather, for the moment the water ceases to boil, the pipes cool off and a considerable time is consumed in starting the heat running again. With hot water there is much more latitude in attention, for though the fires dwindle' the water which fills the pipes will carry heat for a long time, and it will circulate until the last degree is radiated. But a hot-water system costs in the installation about one fourth more than steam. Very small houses may be successfully heated by kerosene stoves, which may be placed inside the house. A much better way would be to use oil heaters for an inside water circulation, carrying off all products of combustion by means of a flue. Coal stoves should never be installed inside the house. It has been done successfully by some amateurs, but the danger of coal gas being driven back into the house by a down draft in the chimney is too great a risk. Coal gas and illuminating gas are two virulent poisons to plants."
It is obvious that the amateur must proceed with great caution in undertaking intensive cultivation under glass. Build at first the simplest and least expensive kind of hotbeds or greenhouses. It takes three to five seasons to train even an experienced farmer along these special lines. Separate crops require special treatment. Do not experiment, but follow well-tried procedure. It is comparatively easy to farm an acre under glass, but it should be worked up to, each step being taken only after a solid foundation is ready to build on. Learn by your mistakes. Don't get discouraged by failure. By not making the same mistake twice, you will soon learn by experience just what is essential to production. The more you learn about the way nature does things, the more likely you will be to succeed when you seek to imitate her.
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