Adequate moisture or water is absolutely necessary to maintain the turgidity of the growing cells since turgidity is the first step towards growth.
The protoplasm is highly dependent on adequate water supply via osmosis. Hence plant growth cannot occur without water.
Light: although not absolutely necessary for initial stage of growth, however, continued or prolonged absence of light is very harmful to the plant. Under certain light intensity, the protoplasm and green leaves. Stomata remain open and chloroplast functions effectively to manufacture plant food in the presence of light.
Suitable temperature or warmth: this is needed for the activities of the protoplasm. At high temperature (usually above 450C), the physiological processes within the protoplasm is brought to a halt (or reduced) as a result of coagulation of the protoplasm. Optimum temperature range is usually 280C. 300C which promotes plant growth while the minimum temperature range is at about 40C
Availability of oxygen or air: the supply of oxygen is vital for the respiration of the cell. The energy released during respiration is consequently used by the protoplasm for its activities. Therefore, growth is enhanced in the presence of oxygen or air.