Hot, humid summer weather may cause poor transpiration resulting to calcium deficiency in the ornamental cabbage. Leaf edge burn (tip burn) is a symptom of calcium deficiency. Calcium is immobile in the plant therefore deficiency symptoms show up first on young growing leaves. In cabbage the young leaves are internal leaves. Margins of the inner leaves may turn brown to black.
Tip burn is a result of temporary inability of the plant to translocate calcium to the young actively growing leaves. Calcium moves in the transpiration stream of the plant and any conditions that interrupt the transpiration stream will prevent the plant from translocating adequate calcium. This will aggravate the tip burn disorder.
Uneven watering, high humidity and rapid growth are some of the causal factors. During periods of high humidity leaves are not transpiring rapidly enough to move adequate calcium to all leaves. Ammonium nitrogen competes with calcium uptake by the plants. Therefore excessive fertilization with ammonium nitrogen inhibits calcium uptake by the plants and also promotes rapid growth that favors tip burn.
To prevent tip burn avoid factors that impair the plants ability to take up and translocate calcium. To correct calcium deficiency, apply supplemental fertilization with Calcium Nitrate (Ca(NO₃) at 200 ppm Ca. New growth should show improvement within 2-3 weeks . Make sure to allow the growing media to dry before irrigating to prevent poor uptake of Calcium.