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.

Reason for deficiency:

Excess alkalinity: Boron becomes unavailable above pH 7.0. Boron deficiency is a common result of over-liming.

Nutrient imbalance: Excess calcium can affect boron uptake.

Lack in soil: Some crops have an affinity for boron and if grown frequently may exhaust the soil reserves, so subsequent crops become deficient. This is most often a problem on light sandy soils where it has been leached away.

Sources of boron:

This is needed in such small quantities it is usually adequately supplied by organic matter. The best way to treat boron deficiency is to add plenty of good compost. Granite dust contains some boron.

Traditionally a boron deficiency was remedied with household borax. It is important to realize that boron is only essential in very small amounts and it’s easy to add too much. The difference between deficiency and toxicity is smaller for boron than any other nutrient. Try an ounce of borax per 1000 square feet (mix it with water or sand) and see how that works. It is easy to add more, but harder to remove. If you use gray water regularly be careful which detergent you use. Some detergents contain potentially toxic amounts of boron.