Bordeaux Mixture Calculator & Copper Sulphate & Lime

Dissolve copper sulphate in part of the water (in a plastic or wooden vessel, never bare metal), slaked lime in another part, then pour the two together while stirring. A 1% mixture is 1 kg copper sulphate plus about 1 kg lime in 100 litres of water. This tool gives the exact amounts for your spray volume and strength.

Classically expressed as copper sulphate : lime : water, e.g. 1:1:100 for a 1% mixture. The strength (%) is the kilograms of copper sulphate per 100 litres of water; lime is usually equal (ratio 1), but good-quality fresh lime can be a little less. Set the strength and ratio and the tool calculates both.

Commonly 0.5% for tender foliage, 1% as a general strength, and up to 2% for dormant sprays on woody plants. Lower strengths reduce phytotoxicity (leaf scorch). The tool supports 0.5%, 1% and 2%; always follow local recommendations for your crop and growth stage.

Copper sulphate alone is acidic and scorches plants. Lime neutralises it, forming insoluble copper compounds that stick to the plant and release copper slowly — protective and longer-lasting while gentle on foliage. Too little lime risks scorch; the right balance is what makes Bordeaux mixture work.

It's a broad-spectrum protectant fungicide and bactericide: potato and tomato late blight, downy mildews (grape, cucurbits), leaf spots, anthracnose, citrus and other cankers, and many bacterial diseases. It acts on contact and must be applied before or at the very start of disease, not as a cure.

Bordeaux mixture deteriorates on standing — it thickens, the particles aggregate and it clogs nozzles and loses effectiveness. Always prepare only what you'll spray that day and use it immediately. Don't store the mixed spray. The tool's per-tank amounts help you mix just what each tank needs.

Yes if misused — too strong a mix, too little lime, application in hot sun or on very tender new growth can cause copper scorch (leaf spotting, russeting on fruit). Use the right strength for the growth stage, ensure adequate lime, spray in cool conditions, and test on a few plants first.

Copper-based fungicides including Bordeaux mixture are permitted in many organic systems, but copper is a heavy metal that accumulates in soil, so use is often capped per year. Use the minimum effective strength and frequency, and check your certification's copper limits. It's a tool to use sparingly, not routinely.

That depends on your spray volume per area (often 500–1,000 L/ha for full cover, less for young crops). Enter the total volume directly, or switch to 'by area' and give your spray volume per hectare and the area; the tool then sizes the copper and lime for the whole job.

Copper sulphate is harmful — wear gloves, goggles and a mask, mix in plastic/wooden (not metal) containers, avoid spray drift onto water (toxic to fish), keep away from children and livestock, and observe the label's pre-harvest interval. Wash thoroughly after handling.