A chief consideration is the temperature of the room in which the plants are to live. If the night temperature falls to between 7 and 10 C., choose only the hardiest kinds, If the minimum night temperature is maintained at 10 to 15C., intermediate plants may be used. Temperatures of 15 to 21C. at night are adequate for even the most tropical kinds. Day temperatures should be 2 to 5C above recommended night temperatures. In summer both day and night temperatures are likely to be higher, which is natural and suitable to the growing season.

Humidity is linked with temperature. The relative humidity of the air increases as the temperature falls. As the temperature rises, unless additional moisture is added to the air, it becomes drier. Modern heating provides good warmth but often dries the atmosphere. It is important, therefore, to keep all plants away from sources of dry heat, such as hot radiators. Never place a plant directly above such heat. All house plants prefer fairly high humidity, and the delicate ones must have it. Naturally, a house cannot be turned into a steaming jungle, but plants can be helped in many ways without interfering with personal comfort.

An easy way to provide additional humidity is to dampen the leaves occasionally with water, using a very fine spray. Fresh air is not essential to house plants, but opening the windows on a mild, calm day will raise humidity; be careful, however, to avoid creating draughts.
Another means of providing humidity is to
place a layer of small pebbles or gravel in the bottom of a shallow tray or saucer about 1 in. deep. Fill this with water just below the surface of the pebbles and stand the plant in its pot on the pebbles. Evaporation will create the humid "micro-climate" the plant thrives in. When watered, the surplus will drain through to the pebble base. Take care that the plant does not stand with its roots in water.
Plants that are grouped usually suffer somewhat less from atmospheric dryness than plants standing alone. Together they give off more water vapour from their soil and foliage than does a single plant, continuously moistening the air in the immediate vicinity.