In connection with the description of the cold pit or greenhouse without fire heat, may be mentioned the combined cellar and greenhouse. Many years ago an accidental circumstance gave me an opportunity of testing the utility of such a structure. An excavation of 20 feet by 40 had been made 7 feet deep, and walled up with stone and beams laid across preparatory to placing a building upon it, when the owner changed his plans and found himself with this useless excavation within a dozen yards of his costly residence. There seemed to be no alternative but to fill it up or plank it over, but both plans were objectionable, and in discussing how to get out of the difficulty, I suggested erecting a low-roofed greenhouse over it, as the owner had a taste for cultivating plants. This suggestion was followed, and the walls were raised one foot above the surface and a span-roofed greenhouse erected over it.
My idea, (which was found to be nearly correct), was, that the large volume of air in the excavation would at no season go below 40°, and be sufficient to keep the upper or greenhouse portion of the structure above the freezing point in the coldest weather. This it did completely when the glass was covered at night with shutters; and the plants with which it was filled, of a kind requiring a low temperature, kept in better health than if they had been grown in a greenhouse having fire heat.
Now, although I have never seen such a combination since, I am satisfied that in favorable circumstances such a structure might be made of great utility and at a trifling cost, for as it dispenses with heating apparatus, which usually is more than half of the whole cost in all greenhouses, the use of a cellar and greenhouse could be had at probably less than the cost of an ordinary greenhouse; and for half hardy plants - plants that will do well in winter if kept only above the freezing point - such a greenhouse will be better for many of them than any kind of greenhouse heated by fire heat. All kinds of Roses, Camellias, Azaleas, Zonal Geraniums, Violets, Cape Jessamines, Carnations, Abutilons, Verbenas, Primulas, Stevias, and, in short, all plants known as cool greenhouse plants, will keep in a healthy, though nearly dormant condition, during the winter months, but they will flourish with greatly increased vigor at their natural season of growth, and flowering as spring advances. Besides, the cellar may be used for the ordinary purposes of such a place; or if exclusively for horticultural purposes, no better place can be had for keeping all deciduous hardy or half hardy plants, Hyacinths in pots to start to flower, or any bulbs of similar nature. The great point to be observed is that the soil where such a structure is to be erected is entirely free from water, or if not so naturally, must be made entirely dry by draining.
The style that I think would suit best for general purposes would be twelve feet in width, and of any length desired. The excavation should not be less than seven feet deep, walled up to about one foot above the surface. When complete it would show something like the section in Fig. 47. If the glass roof is made fixed it should have ventilating sashes 3x3, at intervals of six or nine feet on each side of the roof; if of sashes, they should be seven feet long by three feet wide, every alternate one being arranged to move for ventilation in the usual way. The position of the structure would be best with its ends north and south. The shutters for covering the glass at night should be made of light half-inch pine boards, three feet wide by seven feet long.
Fig. 47. - Greenhouse And Cellar Combined.
It will he understood that the advantage of this combination of cellar and greenhouse over the ordinary cold pit is that the air of the greenhouse is wanned or equalized by mixing with the atmosphere of the cellar, which will rarely be less than 40°. For the same reason, if a high temperature by fire heat were wanted, say 70°, this large body of air from below of 40° would make it difficult to obtain it. It will be necessary, of course, to have the flooring boards covering the cellar wide enough apart to freely allow the passage of the air; this will at the same time give light enough for any operations necessary to be done in the cellar.