Symptoms:
Phosphorus deficiency is most often manifested as purpling of the leaves, particularly the leaf veins. In severe cases the whole plant may take on a purple hue. Tomato roots growing in cold soil, either in the greenhouse or the field, take up phosphorus poorly. Deficient plants lose vigor and yield poorly.

Control:
While phosphorus deficiency due to improper fertility may be a problem in hydroponic, pot culture, and some sandy soil conditions, it is most likely a result of cool root zone temperatures. Plastic mulch will alleviate the problem in early field plantings, and a balanced liquid feed fertilizer will alleviate the problem in greenhouse and pot culture.