Soil acidity: liming, wood ash and correcting pH

In short

• No test, no lime. Measure pH before, and again 12–18 months after.
• To raise pH by one unit you need roughly 150–200 g/m² of ground limestone on sand, 250–300 g/m² on loam and 350–450 g/m² on clay.
• Never give more than 400 g/m² at once: split it over two autumns.
• Calcareous soil (fizzes with vinegar, free lime above about 1 %) is never limed.
• Quicklime and hydrated lime are caustic: goggles, gloves, mask, no wind.
• Wood ash at most 100 g/m² a year; it is no substitute for liming very acid soil.

What's inside

Chapters

1. What pH is and why it matters
2. Measure before you lime
3. How much lime: table by pH and soil
4. Ground limestone, dolomite, hydrated lime or ash
5. How and when to lime
6. Meadow, orchard and polytunnel
7. Safety when working with lime
8. Which plants like which pH
9. When the soil is too alkaline
10. Monitoring after liming
11. Common mistakes
12. Printable checklist

Worksheets

• Lime and sulphur calculator
• Liming plan and log
• Soil acidity map
• Liming and pH calendar