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.
As the various plant-houses are in active operation at this time of year, a few genera] remarks regarding them may be of service.
There are several kinds of structures required where artificial plant-growing is attempted in anything like perfection, or extent of collection; and although, as a general thing, a great diversity of form is not necessary, it has to some extent its advantages. Compact and not large compartments, well-built, close-jointed, and tightly-glassed houses are indispensable where the best culture is expected. Shelter from cold winds and the changeable drafts of our fickle climate, is also of importance; but this shelter should be some distance from the building, that there may be no shade caused thereby, nor the purity of the surrounding atmosphere interfered with. No plants will assimilate the necessary elements or food sufficiently to support healthy growth, and more particularly the flowering and fruiting processes, without an abundance of light; consequently the greatest regard should be paid to this point. We always find double span houses, where the plants are neat the glass, and the light can reflect all around, grow the best specimens, and produce the greatest amount of flowers with brilliancy of color.
Owing to our perverse climate, however, it is not always practicable to employ such unless they be sunk somewhat below the surrounding level, on account of the influcnce of our dry and frigid winds, and the extra amount of artificial heat (which at all times is only a necessary evil) that is required to raise the temperature to the desired height, and followed by a corresponding dryness of atmosphere, unless a large quantity of water is flooded around.
The different houses in use for ornamental plants are technically known as Gold Pit, Forcing Pit, Greenhouse, Intermediate House or Warm Greenhouse, Conservatory, and Stove; and this last may be subdivided into Moist and Dry.
The Cold Pit is merely a preservatory for those plants which need to be protected from severe frost, without the expectation of flowers through the winter. It ought to be built below the ground level, or else a thick bank of turf placed all around the outside up to the top, which is composed of sashes supported on rafters fixed into a framework of timber. Such a house will answer for Camellias, the tender Roses, Violets, Acacias, Oleanders, Myrtles, Laurustinus, Verbenas, Scarlet Geraniums, and many of the general bedding-out plants; but it ought to be understood that a comparative reduction of water at the roots, and also in the atmosphere, should be maintained in accordance with the hibernation of the inmates.
The Greenhouse is expected to furnish flowers at all times of the year, and also keep the plants in health and a growing condition; which, of course, makes it the most generally needed, and when only one is desired, this is that one if flowers are to be produced in the winter season. Artificial heat is required in this house, but the temperature may always be kept low in the night-time. The general range may be from 40 to 45° in the night, with a rise to 60° or 70° with sunlight. Light ought to be a first consideration in this house, and as a very high temperature is not desirable, the double span may be adopted in all cases. In connection with this, the Warm Greenhouse becomes a part, the only difference being, that a temperature from five to ten degrees higher should be maintained. This, however, makes a large item in the extra variety of plants that may be cultivated with satisfaction, and the production of a considerably greater quantity of flowers. Where the means are limited, it will always give greater satisfaction to have a division in the centre of the house, from front to back, and the heating apparatus so arranged that one or both apartments may be worked at pleasure.
Even on the smallest scale this can be accomplished, and a trifling mechanical ingenuity only is required to carry out the suggestion. Among the plants which may be grown and bloomed in the winter, in this arrangement, are the many varieties of Camellia, Erica, Pelargonium, Abutilon, Acacia, Azalea, Burchellia, Fuchsia, Cytisus, Heliotrope, Roses, Habroth-amnus, Melaleuca, Poinsettia, Begonia, Bignonia, Salvia, Rhododendron, Mignonnette and many other annuals, particularly those from California and Australia, Oranges, Cape Jasmines (Gardenia), Kennedys, Jasminum, Bouvardia, many of the Orchids, besides others, of which this list is only a tithe.