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Boron deficiency: how to recognise and treat it

Deficiency

Boron deficiency — Photo: Jan Hinrichs-Berger, LTZ Augustenberg, CC BY 4.0, Wikimedia Commons

Symptoms

Hollow stems and browning heads or curds in cabbage, cauliflower and broccoli.
Brown cracks on the upper side of celery stalks, with reddish-brown tissue inside.
Discoloured flesh or rotting hearts in beetroot, turnips, swedes and celeriac; beetroot may also have rough, cankered patches.
Leaf-tip dieback on lettuce; small, puckered leaves and distorted fruits on strawberries; dimpled pear skin with brown patches in the flesh.

Organic treatment

Before sowing or planting, work in fritted trace elements that contain boron, following the pack instructions.
Borax dissolved in water can be applied to the soil; use only the rate on the label, because the gap between deficiency and toxic excess is narrow.
On alkaline soils, stop liming and, where practical, lower the pH.

Chemical treatment

A foliar spray of boric acid or a soluble borate fertiliser at the label rate; too much boron damages the leaves.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Prevention

Test soil pH; boron is less available to roots above pH 7, so do not lime soil that is already alkaline.
Light, sandy soils lose boron to leaching, so treatment may need repeating on them.
Apply boron-containing fertilisers carefully and evenly — excess boron is toxic to plants.

Plants it affects

Sources

Figures checked against these sources.