Bordeaux Mixture
A traditional combination of copper sulfate and hydrated lime that provides strong fungal and bacterial disease protection, particularly effective on fruit trees and vines.
What it is
Bordeaux mixture was developed in the Bordeaux wine region of France in the 1880s to protect grapevines from downy mildew and remains one of the most effective and widely used organic fungicides globally. It is made by combining copper sulfate (bluestone) with slaked lime (calcium hydroxide). It is certified for organic use in most countries, though soil copper accumulation with heavy use is a concern.
What it does
The combination of copper ions and alkaline calcium hydroxide creates a stable, adhesive compound that bonds firmly to plant surfaces and releases copper ions gradually in wet conditions. The alkaline pH also has some direct antifungal activity. The resulting deposit is more durable and weatherproof than simple copper sulfate solutions, giving longer-lasting protection.
When to use
Apply to fruit trees and vines in late dormancy (at bud swell) for peach leaf curl and apple scab, and again in early spring before wet periods favourable to downy mildew and late blight. On potatoes and tomatoes, begin applications at early disease risk periods. Most effective as a preventive coat applied before infection events.
When not to use
Never apply to actively growing soft young tissue at high concentrations as phytotoxicity is possible. Do not apply during bloom when pollinators are present. Avoid in very hot, dry conditions where the lime component can cause scorch. Limit to the recommended seasonal maximum applications to protect soil biology.
How to apply
- 1
Prepare copper sulfate solution: dissolve 2 teaspoons of copper sulfate in 2 cups of warm water in a non-metal container.
- 2
Prepare lime solution separately: slake 2 teaspoons of hydrated lime in 2 cups of water and stir well.
- 3
Slowly pour the copper sulfate solution into the lime solution while stirring continuously. Never reverse the order. The mixture should turn sky-blue with no excess acidity - test with litmus paper if uncertain.
- 4
Apply immediately using a sprayer (the mixture does not store), coating all plant surfaces thoroughly including stems and the undersides of leaves.
- 5
Repeat applications every 10 - 14 days during wet disease-conducive periods, or after heavy rainfall washes off the deposit.
Garden, by Willowbottom recommends only organic, wildlife-friendly solutions. No synthetic pesticides, no harmful chemicals - ever.