Boron deficiency
A deficiency of growing points and fruit, not leaves — dying tips, hollow brown hearts, corky cracked fruit and flowers that fail to set.
- Nutrient type
- Micronutrient
- Mobility in plant
- Immobile
- Symptoms start on
- Growing points & fruit
- Most at risk
- Sandy, high-pH, leached soils
Overview
Boron holds cell walls together and is essential for pollination and seed/fruit set. Unlike the nutrients that yellow leaves, its shortage attacks the growing points and reproductive parts: shoot tips die back, stems and roots go hollow and brown inside, fruit cracks and turns corky, and flowers drop without setting.
It is immobile in the plant, so the damage is always on the newest growth and the developing fruit. Boron has the narrowest safe range of any nutrient — too little and the crop fails to set, a little too much and it becomes toxic — so correction has to be careful and measured, never a generous "just in case" dose.
How to spot it
- Growing tips and young leaves distort, thicken and die back; the plant may throw out multiple side shoots as the main one dies.
- Stems, roots and hearts go hollow and brown or water-soaked inside — cauliflower and cabbage "browning" / hollow stem, and groundnut "hollow heart" of the kernel.
- Fruit cracks, develops corky brown patches and rough skin — common in tomato, mango, pomegranate and apple.
- Flowering is poor and set fails: cauliflower curds brown, sunflower and mango set few seeds, and coconut sheds buttons.
Why it happens
- Sandy, light soils and heavily leached soils under high rainfall lose boron quickly.
- High soil pH (calcareous or over-limed soils) makes boron unavailable.
- Dry spells reduce boron uptake even where the soil has enough, so symptoms flare in drought.
- Low organic matter — boron is largely held and released by soil organic matter.
Confirm before you spend
- The tell is the target: boron hits growing points, hearts and fruit, not the colour of mature leaves. Hollow stems, corky cracked fruit and failed set point to boron.
- A soil test for boron is worth doing precisely because the safe margin is so narrow — you are dosing to correct a shortfall, not flooding the field.
How to correct it
- Apply borax to the soil at a low, measured rate at sowing/planting (typically around 10 kg/ha borax for a responsive crop like cauliflower — follow the crop’s exact recommendation).
- For a standing crop, spray 0.1–0.2% borax or a soluble boron product on the foliage at the pre-flowering/flowering stage, when set is decided.
- Mix borax thoroughly and apply evenly — never band it concentrated near seed, and never double the rate "to be safe": boron toxicity is as damaging as deficiency.
- Keep the soil evenly moist through flowering, since drought alone can trigger boron-deficiency symptoms.
Prevent it coming back
- Include a small, correct boron dose routinely for high-demand crops (cauliflower, cabbage, groundnut, sunflower) on light or high-pH soils.
- Build organic matter with FYM/compost, the main reservoir that holds boron against leaching.
- Avoid over-liming, which pushes pH up and locks boron away.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My cauliflower curd is turning brown and the stem is hollow. What causes it?
That is classic boron deficiency — "browning" and hollow stem of cole crops. Boron holds the growing tissue together, and cauliflower is one of the most boron-hungry crops. A soil dose of borax at planting plus a 0.1–0.2% borax spray before curd formation prevents and treats it.
Can I just add extra boron to be safe?
No — boron has the narrowest safe range of any nutrient. Slightly too little and fruit and seed fail to set; slightly too much and it becomes toxic, scorching leaf margins and cutting yield. Always use the measured recommended rate, mix it evenly, and never double it as insurance.
Why do symptoms appear in dry weather?
Boron reaches roots dissolved in soil water, so a dry spell can starve the crop of boron even when the soil has enough. Symptoms often flare in drought and ease when moisture returns. Keeping the soil evenly moist through flowering, alongside a correct boron dose, is the practical fix.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.