Boron deficiency doesn’t usually show up in the leaves, so a deficiency may be hard to identify at first glance. It is pretty distinctive though, the most common symptom is internal cracking or rotting of the roots or heart. Less common symptoms include death of the growing point (similar to calcium), slow growth, short stems and distorted terminal leaves. The best way to determine if boron is lacking is with a soil test. Cauliflower, Radish, Rutabaga, Turnip, Beet, Celery and Fava Bean are good indicators of boron deficiency. The interior of roots may rot, while the stems of Brassicas may become hollow.