Boron deficiency
A trace-element shortage that causes hollow stems, brown hearts in roots and brassica heads, and cracked, corky growth.
Also known as: Brown heart, Hollow stem
Symptoms and identification
Cauliflower and broccoli stems are hollow with brown, water-soaked centres and small, brown heads. Beetroot and turnip show dark, corky patches in the flesh. Celery stems crack, and growing tips of many plants die, with thick, brittle, distorted young leaves.
Causes
Boron is washed out of light, sandy soils and is held back in dry soil, so symptoms often appear in drought. Over-liming raises soil pH and locks it up. Boron is needed in very small amounts.
Organic treatment
Improve soil with compost and mulch to hold moisture. Seaweed extract feeds supply small amounts of boron.
Prevention
Keep soil moist and rich in organic matter, avoid over-liming, and test soil in areas where problems have occurred. Rotate crops that need a lot of boron.
Chemical treatment (use with care)
Apply boron very carefully, using a fertiliser or a very dilute borax solution at exactly the label rate, because the gap between enough and too much is small and excess boron is toxic.