Symptoms
The most obvious symptom of calcium deficiency is "tip-burn", which means necrotic lesions on leaf tips and margins. This symptoms develop on inner leaves.
With ongoing Ca deficiency necrosis progresses from tips and margins inwards.
In cabbage symptoms often increase when growth is finished and after harvesting.
Reasons
Calcium deficiency on red cabbage
Many soils contain enough calcium, but restricted Ca uptake leads to calcium deficiency. High content of ammonium, potassium, magnesium or sodium in the soil and water stress (deficiency or excess) induce calcium deficiency.