This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
Having frequently heard complaints, particularly among amateurs, or those who do not keep professional gardeners, of the difficulty of getting a good supply of flowers from their green-houses during the winter months, I thought I would offer a few suggestions on the subject, for their especial benefit, although some of the professional gardeners will no doubt smile at their simplicity; and in doing so, I will endeavor to be as brief as possible.
In the first place, care must be taken that your house is well built, so that it will exclude the outer air.
Second, It must not be too large for the heating apparatus. A small house well heated will produce more flowers than a large one poorly heated.
Third, Have your furnace and stock-hole entirely within the house - Bay under the center stage. This I am aware is objected to by some; but if the flues draw well, which they will be sure to do if there is a regular ascent in them from the furnace to the chimney, and coke or charcoal is used in kindling the fires, you will never be incommoded with smoke or gas, while the additional heat obtained will be at least a fourth. Be careful not to let the earth come in contact with either flues or furnace.
Fourth, Provide a good supply of outer shutters, to use at night.
Fifth, Do not build your house too high, or all the heated air will ascend, and leave the lower part of the house too cold. And this brings us to the most important matter of all, namely, the requisite degrees of heat and moisture to promote health and bloom.
Many amateurs are greatly misled by the directions given in works on gardening, particularly in those published in England, as to the temperature and ventilation. In most of these works the minimum temperature of a green-house is set down at 40°; and consequently the young beginner thinks that so long as he keeps his plants from fretting, he is perfectly safe. This temperature will answer for what are considered strictly green-house plants - such as Camellias, Rhododendrons, Azaleas, Laurustinus, Pittosporums, and other hard-wooded plants; but in a mixed green-house, where there is a large proportion of soft-wooded and herbaceous plants, a much higher temperature must be maintained, in order to have them bloom well. For this purpose the mercury in ordinary winter weather should not fall below 60°, or 55° in very severe weather, and do not be alarmed if it rises to 70° or 75° on a fine bright day. The directions given in English works, and too often followed by English gardeners, in regard to ventilation, are not at all suited to the climate of the Northern and Middle States of the Union. Our atmosphere is so much drier, and our winters so much colder, that much less ventilation will answer.
The difficulty we frequently have to contend with, is that in cold windy weather we have too much ventilation; and I am satisfied that if some of my amateur friends would expend a trifle more in cotton (for filling crevices), coal, and shutters, and less in buying the latest novelties, we should have fewer complaints of the want of boquets during the winter months. While insisting strongly on a high temperature, let me not neglect to enjoin on my readers the importance of supplying the plants with plenty of moisture. The whole matter can be comprehended in a nutshell - keep your fires and syringe going. With a good heat, you can syringe the house almost every bright, sunny morning; whereas, if your house is kept at a low temperature, and you give much moisture, you will find that the foliage will turn yellow, and fall.
My readers will understand that the above directions are given for the management of a mixed collection of plants; but I would recommend, in all cases where it can be done, to divide your house into two compartments; and in that case you can keep the green-house at 40° or 45°, and the hot-house at 65°, minimum.
Another very important matter, and one without which all your other trouble will be of no avail, is the selection of the proper kinds of plants, and also the proper proportion of each kind, as some kinds are much more used in making boquets than others. I subjoin a list of plants which are almost indispensable for winter bloom, and are yet so easily propagated, and at so little cost, that they come within the reach of almost every one. By getting a plant or two, or a package of seeds, of each kind, in the spring, you can by fall propagate a sufficient number to fill your house.