Guide
How to test your soil
A basic soil pH test takes ten minutes and tells you whether your beds need adjustment before the next planting. Most edible crops do best in slightly acid to neutral soil.
Why pH matters
Soil pH affects how available nutrients are to plant roots. At the right pH, iron, calcium, and phosphorus are all accessible. Too acid or too alkaline and the plant struggles to take up what it needs even if the nutrients are present in the soil. Most edible crops prefer a pH of 6.0–7.0, with 6.5 being a reliable target for mixed vegetable beds.
What you need
A basic soil pH test kit - available from most garden centres for a few pounds. These typically use indicator solution dropped onto a small soil sample. More accurate digital probes are available but the kit is accurate enough for practical use. You also need a clean trowel and a small container.
Taking a sample
Take small samples from five or six spots across the bed at a depth of about 10 cm. Mix these together in your container to get a representative reading for the whole bed. Avoid taking samples from the very edges or from spots where you recently added lime or fertiliser, as these will skew the result.
Reading the result
Follow your kit instructions - most ask you to mix a small amount of the soil with water and add the indicator solution, then match the resulting colour to a chart. A reading below 6.0 is acid; above 7.5 is alkaline. A reading of 6.0–7.0 is ideal for most vegetables.
What to do next
If the pH is below 6.0, add garden lime (ground limestone) at the rate given on the packet - typically 150–200 g per square metre for slightly acid soil, more for very acid. If the pH is above 7.5, acidifying compost or sulphur chips can help, though very alkaline soil takes time to change. Re-test three to six months after treatment to see whether the adjustment has taken effect.
When to test
Testing in autumn after clearing crops is ideal - it leaves time to add lime before winter frosts work it into the soil. Spring testing before sowing also works. There is no benefit to testing more than once or twice a year.