For most species, the optimum temperature for rapid root and shoot growth is in the range
of 15-30°C. Generally, species from temperate areas tend towards the lower end of the range, while tropical species grow best at around 30°C. The precise temperature for optimal growth varies with plant species and variety, moisture content of the medium, light intensity and nutrient supply.
Both high and low temperature can inhibit plant growth and, at the extremes, kill plants. The temperature limits to growth vary with
the specific requirements of different plant species. Generally, the lower limit for root growth is about 7°C for temperate species and
12-16°C for tropical species. Root growth is reduced at temperatures above
35-40°C. Roots may be damaged or killed by high temperatures can be reached in pots in hot weather. Roots are killed in a few minutes at 60°C, in about four hours at
50-55°C, or if exposed for more than four hours at 40-45°C, but they may regenerate if exposed for less than four hours at
40-45°C (Handreck and Black
1984). Roots damaged or killed by high temperature are susceptible to attack by pathogens.
Temperature may affect growth indirectly by influencing fertilizer release rates and microbial activity in the potting mix.
