Liming soil, step by step
Interactive lesson: recognise acid soil, measure pH, work out the lime dose, choose the material, spread it safely and prepare meadow, orchard and a blueberry bed.
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The whole lesson as text
1. Acid soil
Plants and the landscape are the first to tell you the soil is acid, or that it has too much lime.
- Rain and rock — Rain slowly washes out calcium and magnesium. Areas with more than 800–900 mm (32–35 in) of rain a year, and soils on sandstone, shale and granite, tend to be acid.
- Acid litter — Conifer woodland, bracken and heather leave an acid litter. Fertilisers containing ammonium, such as ammonium nitrate, urea and sulphate of ammonia, acidify soil over the years.
- Moss and sorrel — On an acid meadow clover disappears, and moss, sorrel and tough grasses take over. In the garden, cabbages stay small and weak.
- Too much lime — Yellow young leaves with green veins on tomatoes, raspberries or pears tell you the soil is too alkaline. Soil like that doesn't need lime.
Why: pH runs from 0 to 14, and 7 is neutral. Soil at pH 5 is ten times more acid than soil at pH 6. Roots can take up the most nutrients between pH 6 and 7.
- Signs on plants are only a warning: check with strips or a lab before you add anything.
- Acid soils are common in the uplands, Wales, Scotland, Cornwall, Devon, on sandy heaths and in the humid eastern US; neutral and alkaline soils lie on chalk and limestone and in the arid West.
2. Measure first
Liming without measuring is like medicine without a diagnosis.
- The lab report — Dose tables go by pH in water. pH in CaCl₂ or KCl is usually 0.5–1 lower; don't mix the two up. From the buffer pH the lab works out the exact dose.
- The vinegar test — If the soil fizzes with vinegar, or free lime is above about 1 %, the soil is calcareous. Soil like that is never limed.
- Soil type by ribbon — Sand feels gritty and won't form a ribbon: light soil. A ribbon up to 2.5 cm is loam: medium soil.
- Heavy and humus-rich soil — A ribbon longer than 2.5 cm that is sticky means clay: heavy soil. For dark soil with more than 5 % organic matter, add 25–50 % to your group.
Why: No test, no lime. On the report you need pH in water, pH in CaCl₂ or KCl, free lime and the lime requirement or buffer pH. The same change in pH needs twice as much lime on clay as on sand.
- If you only have pH in CaCl₂ or KCl, add 0.5 for a rough estimate of pH in water.
- If the lab gives a recommendation, stick to it: 1 t/ha is 100 g/m², and 1 lb per 1,000 sq ft is about 5 g/m².
3. How much lime · Locked
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4. Liming materials · Locked
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5. How and when · Locked
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6. Meadow, orchard, blueberry · Locked
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