Boron
Small dose, big effect on flowering and fruit set — and the one micronutrient where more is definitely not better.
- Composition
- Borax ~11% B; boric acid ~17% B; Solubor ~20% B
- Form
- White powder / fine granules
- Price
- Low (very small dose)
- Best for
- Flowering & fruit/seed set
Overview
Boron governs flowering, pollination and fruit or seed set, plus the movement of sugars and the integrity of growing tips. A shortage shows as flower drop and poor set, hollow or brown stems (cauliflower "hollow stem", "browning"), cracked fruit and dying growing points — symptoms that hit yield directly.
It is genuinely important on cauliflower, mustard, groundnut, sunflower and many fruit and vegetable crops, especially on light, high-pH or leached soils. But boron has the narrowest safety margin of any nutrient: the gap between a corrective dose and a toxic one is small, so it must be applied carefully and evenly, never guessed.
What it is and when to reach for it
- A micronutrient for flowering and fruit set — reach for it on boron-demanding crops (cauliflower, mustard, groundnut, sunflower, tomato) and on light, high-pH soils.
- A soil test is worth doing before a soil application, because boron toxicity is easy to cause.
- For most field crops a well-timed foliar spray at the bud/flower stage is the safest and most effective way to use it.
How to apply it well
- Foliar: spray 0.1–0.2% borax (100–200 g in 100 L water) at the bud and early-flowering stage — this lifts set in pulses, oilseeds and vegetables.
- Soil: apply about 2–4 kg/acre of borax as basal only where a soil test confirms deficiency, and spread it very evenly.
- Dissolve borax in warm water first — it dissolves slowly in cold water and can clog a sprayer.
Common mistakes
- Over-applying "to be safe" — boron is toxic at only a little above the corrective dose, and the damage looks like a disease.
- Uneven spreading of soil boron, which burns the crop in patches.
- Applying boron with no soil test or symptom, on a crop that did not need it.
Organic alternative
Well-rotted FYM / compost
Regular organic matter maintains background boron and buffers availability; a genuine deficiency on a demanding crop still needs a measured borax spray.
Crops it is used on
Open a crop for its full nutrient schedule.
Common questions
Which crops need boron?
Cauliflower and other cole crops, mustard and other oilseeds, groundnut, sunflower, tomato and many fruit crops are boron-demanding. Deficiency is worst on light, sandy, high-pH or leached soils and shows as flower drop, hollow/brown stems and cracked fruit.
How much boron per acre?
For a foliar spray, 0.1–0.2% borax (about 100–200 g in 100 litres of water) at the bud and flowering stage. For a soil dose, only about 2–4 kg of borax per acre and only where a soil test confirms deficiency — spread very evenly, because too much is toxic.
Can too much boron harm the crop?
Yes. Boron has the narrowest safety margin of any plant nutrient — the toxic level is only a little above the useful one. Over-application, or uneven spreading, scorches and stunts the crop. Always measure the dose and, for soil application, confirm with a soil test.
Composition and doses follow ICAR / Soil Health Card guidance; prices are the notified subsidised rates for the season shown and are guidance, not a quote. A soil test for your field always beats a general rate. See our editorial policy.