Soil pH Adjustment Calculator
Calculate how much lime or sulfur to add to adjust your soil pH for optimal plant growth.
Soil Amendment Plan
Soil pH measures the acidity or alkalinity of your soil on a scale from 0 to 14. Most plants grow best in soil with a pH between 6.0 and 7.0. Adjusting pH ensures plants can absorb nutrients effectively.
pH Scale Reference:
| pH | Classification | Common Plants |
|---|---|---|
| 4.5–5.5 | Strongly acidic | Blueberries, azaleas, rhododendrons |
| 5.5–6.0 | Moderately acidic | Potatoes, strawberries |
| 6.0–6.5 | Slightly acidic | Most vegetables, flowers, herbs |
| 6.5–7.0 | Neutral | Lawns, beans, lettuce |
| 7.0–7.5 | Slightly alkaline | Asparagus, beets, cabbage |
| 7.5–8.0 | Moderately alkaline | Some desert plants |
To raise pH (more alkaline) — add lime:
- Ground limestone (calcium carbonate): most common, slow-acting
- Dolomitic limestone: adds magnesium too
- Application rates vary by soil type — clay soils need more than sandy soils
To lower pH (more acidic) — add sulfur:
- Elemental sulfur: most effective, slow-acting (3–6 months)
- Iron sulfate: faster but needs 6× more material
- Aluminum sulfate: fastest but can be toxic in excess
Amendment rates (approximate per 100 sq ft / 9.3 m²):
Lime to raise pH by 1 point:
| Soil Type | Amount Needed |
|---|---|
| Sandy | 1.5 kg (3.5 lb) |
| Loam | 3.5 kg (8 lb) |
| Clay | 5 kg (11 lb) |
Sulfur to lower pH by 1 point:
| Soil Type | Amount Needed |
|---|---|
| Sandy | 0.5 kg (1 lb) |
| Loam | 1 kg (2.5 lb) |
| Clay | 1.5 kg (3.5 lb) |
When to use this calculator:
- Preparing garden beds for specific plants
- Correcting pH after a soil test
- Establishing blueberry patches (need acidic soil)
- Improving lawn health
Tips:
- Always test your soil pH before amending — guessing can make things worse.
- Apply amendments in fall for best results; they take weeks to months to fully work.
- Never change pH by more than 1 point per season.
- Retest soil 2–3 months after application to check results.
- Organic matter (compost) gradually moves soil toward neutral pH over time.