Phosphorus deficiency

Phosphorous deficiency can be caused by a number of factors. It is most common in areas of high rainfall, especially on acid, clay or poor chalk soils. Plants also require warmth to take up the phosphorus in the soil, so cold weather can cause a temporary deficiency.

All plants may be affected, although this is an uncommon disorder. Particularly susceptible are carrots, lettuce, spinach, tomatoes, apples, currants and gooseberries.

Symptoms
Symptoms include poor growth, and leaves that turn blue/green but not yellow - oldest leaves are affected first. Fruits are small and acid tasting. Phosphorus deficiency may be confused with nitrogen deficiency. Undersides of tomato plant leaves, and the veins and stems, may turn purple. stiff, stunted plants with purlish tinge.

Treatment
It can be controlled by applying organic sources of phosphorus such as rock phosphate or a high-phosphorus fish fertilizer applied as a soil drench or foliar feed.

Plants that are naturally adapted to low levels of available soil phosphorus, however, are more likely to suffer from phosphate poisoning: the key is to provide the right level for any particular plant type, neither too high nor too low.