Copper Sulphate
A small-dose copper micronutrient — and the blue crystals behind Bordeaux mixture. Rarely needed as a fertiliser, but important where it is.
- Composition
- Cu ~24% (as sulphate)
- Form
- Blue water-soluble crystals
- Price
- Moderate (very small dose)
- Best for
- Copper deficiency; Bordeaux mixture
Overview
Copper is needed only in tiny amounts, and copper deficiency is uncommon on most Indian soils — but it does occur on peaty, organic, sandy and newly reclaimed soils, where it shows as dieback of growing tips, twisted young leaves and, in cereals, white-tip and poor grain fill ("reclamation disease"). Copper sulphate (about 24% Cu) is the standard corrective.
The same blue crystals are the copper source in Bordeaux mixture, a classic protective fungicide, so many farmers already know the material. As a nutrient it is used sparingly: the gap between a corrective dose and a toxic one is narrow, so it should only go on where a soil test or clear symptoms confirm a genuine shortage.
What it is and when to reach for it
- A copper micronutrient for the uncommon case of copper deficiency — reach for it on peaty, sandy or newly reclaimed soils where cereals show dieback and white-tip.
- Confirm the need with a soil test or clear symptoms first; most soils never require it.
- The same product is the copper in Bordeaux mixture, used as a protective fungicide — a separate use from feeding the crop.
How to use it well
- Foliar: a dilute spray (well under 0.5%, per local recommendation) corrects a deficiency; keep the dose low because copper is easily over-applied.
- Soil: a small basal dose only where a soil test confirms deficiency — copper persists in soil, so it is not an every-season need.
- For Bordeaux mixture, follow the standard copper-sulphate-and-lime recipe and freshly prepare it for spraying.
What it can and cannot do
- It corrects a genuine copper shortage; on soils that are not copper-deficient it does nothing useful and risks toxicity.
- Copper is toxic to plants (and to fish and soil life) in excess, and it builds up in the soil, so repeated heavy use is harmful.
- Its narrow safety margin means the dose must be measured and kept low — never applied by guess.
Common mistakes
- Applying copper without a confirmed deficiency, risking toxicity for no benefit.
- Over-dosing "to be safe" — copper toxicity stunts roots and can poison the soil.
- Confusing its fungicidal use (Bordeaux mixture) with a routine nutrient need.
Crops it is used on
Open a crop for its full nutrient schedule.
Common questions
When is copper sulphate needed as a fertiliser?
Rarely — copper deficiency is uncommon and mainly occurs on peaty, organic, sandy and newly reclaimed soils, where cereals show dieback, twisted young leaves and white-tip. Only apply it where a soil test or clear symptoms confirm a shortage; most soils never need it.
Is copper sulphate a fungicide or a fertiliser?
Both, in different roles. As a fertiliser it corrects copper deficiency in tiny doses. As the copper source in Bordeaux mixture (with lime) it is a classic protective fungicide. The two uses are separate — do not treat routine fungicidal spraying as feeding the crop copper.
Can too much copper harm the soil?
Yes. Copper is toxic in excess — it stunts roots, harms soil life and fish, and accumulates in the soil over time. Its safety margin is narrow, so keep doses low, apply only on a confirmed deficiency, and never over-apply to be safe.
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.