Nutrients

Nitrogen is an essential growth nutrient and is required for the growth of leaves and stems. Deficiencies manifest themselves through weak, stunted growth and yellowing of older leaves. However, excess nitrogen can also be detrimental to the plant causing such effects as disproportionate leaf growth at the expense of other parts of the plant (e.g. flowers).

Phosphorous is essential for root growth and development. Deficiencies may be seen through stunted root systems whilst the leaves on some plants may also exhibit a dull green or purple coloration.

This nutrient performs an important photosynthetic function within the plant, whilst also promoting flower and fruit development. Deficiencies may be seen through the yellowing and death of marginal (and older) leaf tissue, whilst low levels also make the plant more susceptible to diseases.

Magnesium is a constituent of chlorophyll, the green pigment which enables plants to photosynthesise. It is required by the roots and micro-organisms to protect them from pathogens and to stabilise the very important soil that touches the roots' surfaces called the rhizospheres (zones around the roots).

Magnesium deficiencies may be noted by the interveinal yellowing of the plant's older leaves.