Soil pH Adjustment Calculator
Calculate how much lime or sulfur to add to adjust your soil pH.
Enter current pH, target pH, soil type, and area for accurate amendment amounts.
How Soil pH Adjustment Is Calculated
Soil pH determines nutrient availability to plants. Most vegetables and flowers thrive at pH 6.0–7.0. Outside this range, nutrients lock up even if present in the soil.
pH Scale Reference:
- pH < 6.0: acidic (iron, manganese become toxic; phosphorus, calcium unavailable)
- pH 6.0–7.0: ideal for most plants
- pH > 7.5: alkaline (iron, manganese, zinc deficiency common)
Amendment Quantities:
To raise pH (make less acidic): add garden lime (calcium carbonate)
Lime (kg/m²) = (Target pH − Current pH) × Lime Factor
To lower pH (make more acidic): add sulfur
Sulfur (g/m²) = (Current pH − Target pH) × Sulfur Factor
Factors depend on soil texture (clay needs more amendment than sandy soil).
Typical Application Rates (per 10 m²):
| Soil Type | Lime to raise 1 pH unit | Sulfur to lower 1 pH unit |
|---|---|---|
| Sandy | 1.0–1.5 kg | 100–150 g |
| Loam | 2.0–2.5 kg | 150–250 g |
| Clay | 3.0–4.0 kg | 250–400 g |
Worked Example: Clay garden bed (10 m²), current pH 5.5, target pH 6.5:
- Lime needed = 1.0 pH unit × 3.5 kg/unit = 35 kg of garden lime
Important Notes:
- Test pH 6–8 weeks after applying amendments — it takes time to react
- Apply lime in autumn for spring planting
- Never apply lime and fertilizer simultaneously — chemical reactions reduce both
- Blueberries, azaleas, and rhododendrons prefer pH 4.5–5.5 — do not raise pH for these