Next in importance to light, is the matter of temperature. The ordinary house plants, to be kept in health, require a temperature of sixty-five to seventy-five degrees during the day and fifty to fifty-five degrees at night. Frequently it will not be possible to keep the room from going lower at night, but it should be kept as near that as possible; forty-five degrees occasionally will not do injury, and even several degrees lower will not prove fatal, but if frequently reached the plants will be checked and seem to stand still. Plants in the dormant, or semi-dormant condition are not so easily injured by low temperature as those in full growth; also plants which are quite dry will stand much more cold than those in moist soil.
The proper condition of temperature is the most difficult thing to regulate and maintain in growing plants in the house. There is, however, at least one room in almost every house where the night temperature does not often go below forty-five or fifty degrees, and if necessary all plants may be collected into one room during very cold weather. Another precaution which will often save them is to move them away from the windows; put sheets of newspaper inside the panes, not, however, touching the glass, as a “dead air space” must be left between. Where there is danger of freezing, a kerosene lamp or stove left burning in the room overnight will save them. Never, when the temperature outside is below freezing, should plants be left where leaves or blossoms may touch the glass.
As with the problem of light, so with that of temperature–the specially designed place for plants, no matter how small or simple a little nook it may be, offers greater facility for furnishing the proper conditions. But it is, of course, not imperative, and as I have said, there is probably not one home in twenty where a number of sorts of plants cannot be safely carried through the winter.
It would seem, at first thought, that the proper condition of moisture could be furnished as easily in the house as anywhere. And so it can be as far as applying water to the soil is concerned; but the air in most dwellings in winter is terribly deficient in moisture. The fact that a room is so dry that plants cannot live in it should sound a warning to us who practically live there for days at a time, but it does not, and we continue to contract all sorts of nose and throat troubles, to say nothing of more serious diseases. No room too dry for plants to live in is fit for people to live in. Hot-air and steam heating systems especially, produce an over-dry condition of the atmosphere. This can be overcome to a great or complete extent by thorough ventilation and by keeping water constantly where it can evaporate; over radiators, etc. This should be done for the sake of your own health, if not for that of the plant.