Boron is a micronutrient, needed by plants in small amounts. A deficiency can cause poor and stunted growth and a range of other symptoms, depending on the plant.
- Stunted and poor growth
- Leaf tip browning and dieback
- A range of other symptoms, depending on the plant
What is boron deficiency?
Boron (B) is one of the micronutrients or trace elements, needed by plants in small or trace, but essential, amounts. It is important in plant cell formation and both vegetative and reproductive growth. A deficiency in the soil leads to poor and stunted growth and reduced fertility.
Other symptoms appear in plants, depending on the plant in question. These include:
- Apple: ‘water core’ in the fruit
- Beetroot: rough, cankered areas on the skin and internal brown rot
- Cabbage: distorted leaves and hollow stems
- Cauliflower; poorly developed curds with brown patches
- Celery: brown cracks in leaf stalks, coloured reddish brown inside
- Celeriac: brown heart rot
- Lettuce: stunted growth and leaf tip dieback
- Pear: new shoot dieback, fruit skin develops hard brown flecks and brown patches underneath
- Strawberry: small, yellow leaves and small, pale fruit
- Swede and turnip: brown concentric rings inside roots, leading to rotting
Although shortages of boron in the soil are not common, boron deficiency may be caused when there are insufficient suitable boron-containing materials in the growing medium (soil or compost). It is more likely to occur when boron is present, but is unavailable for plant roots to absorb – “locked” in the soil or compost. This is common in alkaline growing media, where the pH is above 7. It can also be caused when plants are growing in dry soil or compost, which prevents the roots taking up the boron.
Use a simple soil pH testing kit to make sure your soil is acidic – especially when growing lime-hating and ericaceous plants and those plants listed above.
What does it affect?
- Most plants can be affected
- But, in particular, apple, beetroot, cabbage, cauliflower, celery and celeriac, lettuce, pear, strawberry, swede and turnip
How to prevent boron deficiency
Keep soil boron levels topped up by feeding with a granular fertiliser that contains boron, especially in spring. Ericaceous and lime-hating plants should be fed with an ericaceous fertiliser.
Suitable liquid feeds will get to work sooner than dry, granular feeds.
Where boron deficiency occurs, apply borax to the soil before sowing or planting vegetables or use as a foliar feed.
Grow plants as well as possible, so they never go short of water. The soil or compost should be kept consistently moist, never allowing it to dry out, without cycles of drying out followed by overwatering.
Make sure soils contain lots of bulky organic matter to hold soil moisture and nutrients. This is particularly important on light, sandy and chalky soils, which contain little organic matter.
Covering the soil with a 5-7.5cm (2-3in) thick mulch will help conserve moisture.
Avoid growing lime-hating and ericaceous plants in multi-purpose and John Innes composts, as these contain lime. Instead, use an ericaceous compost or John Innes Ericaceous Compost.
If you live in an area with chalky/”hard” water, which is alkaline, watering plants, especially container plants, with tap water will gradually increase the pH of the growing medium. To neutralise this, treat with Sulphur Chips every six months – once in spring and once in autumn.
- Ericaceous fertilisers
- Ericaceous composts
- Sulphur Chips
- Soil pH testing kits