Factors that affect growth are Light, temperature, water supply, oxygen. Light: Its effects can be grouped under intensity, duration and quality. Intensity refers to the brightness and based on this requirement plants are grouped as Heliophytes and sciophytes. Heliophytes require bright sunlight, if not available they tend to show etiolated conditions and internodes are considerably long.
Duration is the response of plants to varying periods which they are grouped as Long day, short day and day-neutral plants. This phenomenon was studied by Garner and Allard quality is wavelength and in general, plants grow best in visible light.
Temperature:
This directly affects the action of enzymes which function best within an optimum range. Temperature influences plant growth in the case of flowering and the process is called vernalization. For some plants mainly biennials flowering is governed by photoperiod and temperature. It is the low temperature during the first year that influences the response.
Water:
It is required for all the fundamental processes, of the protoplasm and is essential for cell enlargement as it increases turgidity.
Oxygen:
The Vital activities are dependent on the release of metabolic energy by respiration. The energy held in the chemical bond of fuel molecules can be released which stimulated growth.
