Nutrient Deficiencies in Plants
Nitrogen
Leaves become pale with spindly stalks. Feed once with an atlpurpose, balanced fertiliser.
Potassium
Plants are slow to grow and leaves may roll up slightly at the edges. Apply a one-off, all-purpose fertiliser. Potassium is also important in fruit production and a major ingredient in tomato fertilisers.
Calcium
Blossom end rot in tomatoes is caused by a lack of calcium. Water regularly to ensure that calcium in the compost is transferred to developing fruits.
Magnesium
Can Show itself as chlorosis (patchy yellowing of the leaves which can turn brown). Spray leaves with diluted Epsom salts.
Iron
Veins on leaves are dark but therest of the leaf is yellowy. Apply an iron tonic such as sequestrene.