Soil pH tester: which kind to trust
Skip the two-prong probe. A colour-chart kit gives a reading you can act on.
When researchers at the University of Wisconsin–Stevens Point and The Morton Arboretum tested 21 field meters against a lab-grade glass electrode, the cheap metal-probe meters showed no meaningful link to the true pH, while glass-electrode meters tracked it closely (Scheberl et al., 2017). For most gardens, a chemical colour-chart kit is the cheap way to a number you can act on. Then lime raises the pH and sulphur lowers it.
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- Two-prong probe meters with no battery: not reliable for pH.
- Colour-chart kit: good enough to choose lime, sulphur or nothing.
- Glass-electrode meter or a lab test: for a big project, or frequent testing.
Soil pH testers compared
| Type | How it did | Cost | Use it for |
|---|---|---|---|
| Two-prong metal probe, no battery | No meaningful link to true pH in a 2017 university test | A few pounds | Not pH |
| Colour-chart kit with chemical reagent | Close enough to choose lime, sulphur or nothing | A few pounds | Most gardens, once a year |
| Digital meter with a glass electrode | Tracked the reference closely (r = 0.96 to 0.97) | Over £100; needs calibrating | Keen growers testing often |
| Laboratory test | The most accurate | Posted off; takes a week or two | A big change, such as a new blueberry bed |
Probe and glass-electrode results: Scheberl, Scharenbroch and Fite (2017), 21 sensors on four soils at three moisture levels, against a Hach glass electrode. The study found sensors read best in a soil and deionised water mix, and that cost was a strong guide to quality.
What your reading means
| Reading | What it means | What to add |
|---|---|---|
| Below 5.5 | Acid. Fine for blueberries and rhododendrons; too low for most else | Lime, about 0.7 to 1.8 kg per m² by soil type |
| 5.5 to 6.0 | Slightly acid. Fine for camellias; low for veg | Lime, about 0.4 to 1.0 kg per m² by soil type |
| 6.0 to 7.0 | The sweet spot for most plants | Nothing |
| 7.0 to 7.5 | Slightly alkaline. Too high for acid-lovers | Sulphur, only where acid-lovers grow |
| Above 7.5, fizzes with vinegar | Chalky, with free lime | Grow acid-lovers in pots of ericaceous compost |
Lime rates for beds from the RHS liming table; lawns need less. Sulphur rates on our Sulphur Soil Acidifier page. Full method for taking the sample: how to test soil pH.
Work out your exact amount. Put your reading, your area and your soil type into the soil pH calculator for the exact amount of lime or sulphur, and when to apply it.
Common questions
Are soil pH meters accurate?
The cheap two-prong probe meters are not. In a 2017 test of 21 sensors, the metal-probe types showed no meaningful correlation with the true pH, while glass-electrode meters costing over £100 tracked it closely (Scheberl et al., 2017).
Do 3-in-1 moisture, light and pH meters work?
The pH reading on those is the same metal-probe design that failed the 2017 test. Use a colour-chart kit for pH.
Can I test soil pH without a kit?
Only roughly. Vinegar on a dry spoonful of soil is a sound check: fizzing means free lime, so the soil is alkaline (RHS). No fizz does not tell you the soil is acid. For a number, use a kit.
Is a lab soil test worth it?
Before a big change, such as a new blueberry bed or liming a whole plot, yes. For a yearly check on beds, a colour-chart kit is enough.
How often should I test soil pH?
Before you add lime or sulphur, then three to six months after. Once a bed is in range, every two or three years. Never straight after lime, manure or fertiliser, which skew the reading.
More: how to test soil pH · soil pH calculator · acidic soil · how to raise soil pH · how to make soil more acidic
Test, then correct
Below your target, lime raises the pH. Above it, sulphur lowers it. Both packed in Stockport.
Buy what your reading calls for
Free UK delivery over £40. Buy now goes straight to checkout.
Free UK delivery over £40. Dispatched in 1 to 2 working days. Packed and posted from Stockport.