Boron Deficiency
Risk near you, next 48h
See whether your local forecast favours this disease right now.
When it strikes
Fix the cause, not the leaf
No spray will help here. The trigger is soil, water supply, nutrition or temperature, so change the growing condition and judge the result on new growth, not on damaged leaves.
Not contagious
Nothing spreads from plant to plant here. Neighbouring plants showing the same signs are reacting to the same soil, water or weather, so fix the cause rather than isolating plants.
Safe to compost
No pathogen carries over on this material, so it can go on an ordinary heap with the rest of the garden waste.
When and where to look
Scout the planting in dry air below 45%.
The signs that lead here
Full problem lists for these crops
About
Boron is needed in tiny amounts but is essential for cell wall formation and pollination. It leaches readily from light soils and becomes unavailable in dry weather and in over-limed ground, so beetroot, celeriac, swede and cauliflower are the usual casualties.
Symptoms
Brown, corky patches inside beetroot, swede and celeriac roots. Cauliflower curds go brown and the stem is hollow with a brown lining. Growing points die, young leaves are brittle and distorted, and fruit sets poorly.
Organic Treatment
Keep the soil evenly moist — a large part of apparent boron deficiency is simply drought stopping uptake. Add well-rotted compost, which supplies boron slowly and steadily, and stop liming the affected bed.
Chemical Treatment
Borax at roughly 3 g per square metre, dissolved in water and applied evenly, corrects a genuine deficiency. Take the dose seriously: boron is toxic to plants only slightly above the useful rate, so never guess and never re-apply routinely.
Prevention
Do not over-lime, mulch to keep the soil moist through summer, and rotate demanding crops. On known light, sandy soils, a single measured borax application every three or four years is the safe pattern.
Crops at risk
Related problems
Boron Deficiency risk by location
Each location has a month-by-month profile computed from the weather archive: how many hours a year actually meet this disease’s thresholds.