How much lime do I need to raise soil pH by 1 point?

It depends on soil type. Using ground limestone (per the RHS/DEFRA table), a 1.0 pH rise from 5.5 to 6.5 needs roughly: sandy soil about 700 g/m² (0.7 kg/m²), loam about 800 g/m² (0.8 kg/m²), clay about 1,000 g/m² (1 kg/m²), and peat about 1,200 g/m². Clay and peat soils have higher buffering capacity and need more lime to shift pH. Always test first and re-test before re-applying.

Is pelletised lime better than powdered?

Pelletised lime is easier to spread and less dusty, but slightly less effective weight-for-weight (about 80% as effective as powdered). To match the same neutralising effect you therefore need about 25% more by weight (1 ÷ 0.8 = 1.25), and the calculator adjusts quantities accordingly. Pelletised is better for small garden applications; powdered for large areas.

How often can I apply lime or sulphur?

Avoid changing pH by more than 0.5 units at a time with lime, or 0.3 units with sulphur. Wait at least 3 months between applications and retest before adding more. Over-liming is difficult to reverse.

When is the best time to apply lime?

Autumn is ideal — lime has time to react over winter before spring planting. Avoid applying lime at the same time as manure or fertiliser, as it can cause nitrogen loss. Leave at least a month between lime and other amendments.

How do I lower soil pH for acid-loving plants?

Use flowers of sulphur at the rates shown by the calculator. For quicker results on small areas, use sulphur chips or acidifying fertilisers. Ericaceous compost and pine needle mulch also help maintain lower pH over time.

pH Amendment Calculator — Free Soil & Compost Tool

pH Amendment Calculator — Lime & Sulphur for Soil pH

Calculate how much lime or sulphur you need to adjust your soil pH.

Current pH

Measured pH from a soil test kit (most UK garden soils sit between 5.5 and 7.5)

Target pH

Aim for 6.5 for most veg and grass; 5.5 or lower for ericaceous (acid-loving) plants

Area

Bed or plot area being limed — lime is worked into the top 20 cm

Soil TypeHeavier soils (clay, peat) buffer pH and need more lime to shift; sandy soils need least

How We Calculate This

This calculator uses buffer-capacity rates that vary by soil type to determine amendment quantities. Lime rates follow the RHS/DEFRA ground-limestone table (target pH 6.5, incorporated into the top 20 cm), read for a 1.0 pH unit raise (pH 5.5 → 6.5).

Lime rates (ground limestone, to raise pH by 1.0)

Sandy: 700 g/m² (0.7 kg/m²)
Loam: 800 g/m² (0.8 kg/m²)
Clay: 1,000 g/m² (1 kg/m²)
Peat: 1,200 g/m² (very high buffering)

Sulphur rates (flowers of sulphur, to lower pH by 1.0, top 15 cm)

Sandy: 135 g/m²
Loam: 200 g/m²
Clay: 270 g/m²
Peat: 320 g/m² (very high buffering)

Sulphur rates follow the RHS ‘Acidifying soil’ guidance (135 g/m² sandy to 270 g/m² clay for a ~1.0–1.5 unit drop, incorporated into the top 15 cm), read here as a cautious per-1.0-unit rate.

Applications are split to avoid changing pH by more than 0.5 (lime) or 0.3 (sulphur) units at a time.

Frequently Asked Questions

Last updated: March 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.

pH Amendment Calculator — Lime & Sulphur for Soil pH

How We Calculate This

Lime rates (ground limestone, to raise pH by 1.0)

Sulphur rates (flowers of sulphur, to lower pH by 1.0, top 15 cm)

Frequently Asked Questions

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