Temperature is an important factor in the growth of plants, but their individual requirements vary widely. This is particularly true of houseplants because of their diverse natural habitats. Many foliage plants, for instance, are natives of the tropics whilst others are from more temperate regions. Flowering houseplants generally show less variation and most do best in cool to average temperatures. One exception to this general rule is that bromeliads may need to be kept at 24°C (75°F) if they are to produce flower buds. Even these exotic plants, however, will survive quite happily in more normal temperatures once they have come into flower.
Normal house condition
A modern, centrally heated house where the day temperature does not normally rise above 21°-24°C (70°-75°F) and the night temperature is above 10°C (50°F) can provide an ideal location for all types of houseplants. In fact, too much heat is detrimental even to exotic tropical species. In their natural habitats the high temperatures are balanced by bright light. Lighting levels indoors are much lower, so if the temperature is too high the plants become drawn up and spindly. High temperatures also tend to shorten the flowering period.
Most popular flowering plants flourish best in cool to average heat but will survive quite well in centrally heated homes provided that they are kept in a brightly lit position. More difficulty is experienced with those that prefer rather cool conditions. This class, which includes azalea, Beloperone, Browallia, chrysanthemum and cyclamen, have only a short life indoors unless they are kept in well lit and really cool positions.
Another limiting factor, particularly in centrally heated homes, is dryness of the atmosphere. In such conditions most plants transpire very freely, losing a lot of water from their foliage. The rate of this water loss increases as the temperature rises and can reach the point where it exceeds the supply from the roots. Consequently the leaves dry up and wilt and, in extreme cases, can turn brown at the edges and fall prematurely. This type of damage can be prevented by increasing the humidity of the air surrounding the plants and the various ways of achieving this are described on humidity link.
Although it must be accepted that too high temperatures can be damaging to some plants it should also be realised that it is possible to minimise any ill effects by increasing the humidity of the air which surrounds them and at the same time giving them as much light as possible — even a few bowls of water in a room can help.
There are no such remedies for the injurious effects of excessively low temperatures. Consequently, homes where the temperature lls below 15°C (60°F) are not suitable for tender species such asAcalypha, Aglaonerna , Anthurium, Caladiwn, Cczlathea, Cissus discolor, Dieffenbachia, Dizygotheca and Syrigonium. Most other types will survive a drop to 10°C (50°F) whilst a few hardy plants such as aspidistra, Maranta, Rhoicissus and tradescantia will tolerate temperatures as low as 4.4°C (40°F).
Types of houseplants based on temperature need
On the basis of their heat requirements houseplants can be divided into three main classes as follows:
Require a minimum temperature of 15°C (60°F) but will flourish in temperatures up to 24°C (75°F) provided that the humidity is high enough.
These do best in cool to average temperatures. They will survive a minimum temperature of 10°C (50°F) but do best in the range 13-21°C (55-70°F).
Tolerate a minimum temperature as low as 4.4°C (40°F) and yet flourish in normal room temperatures.
Handling Temperature drop
All plants tolerate a small overnight drop in temperature so this is not normally a problem. Major lowering of the temperature, such as can occur near windows in frosty weather can, however, be damaging, particularly if the plants are trapped between drawn curtains and the window. Consequently it is advisable to move plants from the window sill in the evening before drawing the curtains — draw the curtains early so as to retain as much warmth as possible. Remember too that both doors and windows can be a source of draughts which are harmful to plants. Cacti are the exception to this rule since very low night temperatures are a feature of their natural desert habitat, so they find
it easy to adapt.