Young corn plants often turn purple as a result of a phosphorus deficiency. Phosphorus deficiency symptoms begin on lower leaf tips and progress along leaf margins until the entire leaf shows purpling. New leaves emerging from the whorl are usually green but may turn purple shortly thereafter. Phosphorus deficiency symptoms often occur as young plants are exposed to good growing conditions following cool, wet conditions. This weather pattern results in a lag phase where vegetative growth exceeds the roots' ability to supply phosphorus.
Young plants are especially vulnerable because their root systems are small.
Plants normally recover when favorable growing conditions allow root expansion. Leaf symptoms usually disappear before plants get 2 to 3 feet tall, even in low-phosphorus soils. However, phosphorus deficiency will likely reduce yield by delaying maturity, decreasing root growth, and reducing energy transfer and storage. Many cultural or environmental factors may limit root growth, aggravating phosphorus-deficiency symptoms. Soil pH less than 5.5 may reduce the availability of phosphorus in the soil solution by more than 30 percent.