Soil pH to Nutrient Availability Converter
See how soil pH affects nutrient availability for plants.
Enter your soil pH to check which nutrients are optimally available and which may be locked out.
Enter your soil pH to see nutrient availability. Add a target pH, an area and a soil texture and it will also work out how much lime or sulfur to spread.
Understanding Soil pH and Nutrient Availability
Soil pH is a measure of acidity or alkalinity on a scale from 0 to 14. A pH of 7.0 is neutral. Values below 7 are acidic, and values above 7 are alkaline (basic). Most garden plants thrive in slightly acidic to neutral soil, typically between pH 6.0 and 7.0. The pH level directly controls which nutrients dissolve into the soil water and become available for plant roots to absorb.
The pH Scale and Soil:
The pH scale is logarithmic, meaning each whole number change represents a tenfold difference in acidity or alkalinity. Soil at pH 5.0 is ten times more acidic than soil at pH 6.0, and one hundred times more acidic than soil at pH 7.0. This is why even small pH adjustments can have a dramatic effect on nutrient availability.
Nutrient Availability by pH Range:
| Nutrient | Best Availability pH | Notes |
|---|---|---|
| Nitrogen (N) | 6.0 - 8.0 | Bacterial activity drops below 6.0 |
| Phosphorus (P) | 6.0 - 7.5 | Locks up in acidic and alkaline soils |
| Potassium (K) | 6.0 - 7.5 | Generally available in wide range |
| Calcium (Ca) | 6.5 - 8.5 | Deficient in very acidic soils |
| Magnesium (Mg) | 6.0 - 8.5 | Similar to calcium |
| Sulfur (S) | 6.0 - 8.0 | Widely available |
| Iron (Fe) | 4.0 - 6.5 | Locks up above pH 7.0 |
| Manganese (Mn) | 5.0 - 6.5 | Toxic at very low pH |
| Zinc (Zn) | 5.0 - 7.0 | Less available in alkaline soil |
| Copper (Cu) | 5.0 - 7.0 | Similar to zinc |
| Boron (B) | 5.0 - 7.0 | Leaches in acidic, locks in alkaline |
| Molybdenum (Mo) | 7.0 - 8.5 | Opposite of iron |
The Sweet Spot:
Most nutrients are simultaneously available between pH 6.0 and 7.0. This is why most gardening guides recommend maintaining soil in this range. At pH 6.5, nearly all essential nutrients are at or near peak availability. Blueberries, azaleas, and rhododendrons are notable exceptions that prefer acidic soil around pH 4.5-5.5.
Adjusting Soil pH:
- To lower pH (make more acidic): elemental sulfur, aluminium sulfate, or acidic organic matter like pine needles
- To raise pH (make more alkaline): agricultural lime (calcium carbonate) or wood ash
- Changes take weeks to months to fully take effect in the soil
How much to add
Fill in an area and a target above and the calculator works it out. The rates it uses are the standard extension-service figures, in pounds per 100 square feet to move the pH by one full unit:
| Soil texture | Lime, to raise 1 unit | Elemental sulfur, to lower 1 unit |
|---|---|---|
| Sandy | 3.5 lb | 1.2 lb |
| Loam | 7.5 lb | 2.3 lb |
| Clay | 10 lb | 2.8 lb |
Clay needs roughly three times what sand does for the same movement. That is buffering capacity: clay particles and organic matter hold a reservoir of exchangeable ions, so they resist a change that sand simply gives in to. It is also why a sandy soil that was limed two years ago has probably drifted back.
Three rules that matter more than the exact number:
- Do not move more than one pH unit in a season. Overshooting alkaline is much harder to undo than overshooting acid.
- Retest after three months, not three weeks. Lime is slow, and sulfur depends on soil bacteria that barely work in cold ground.
- Wood ash is not lime. It works, but it is far more soluble and much easier to overdo, and it adds potassium you may not want.
How we build and check this converter
This converter runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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