Soil pH
Soil Health
Soil pH describes whether soil is acid, neutral or alkaline, on a scale centred on pH 7. It affects how easily plants can take up nutrients and which crops are comfortable in a bed. Most UK vegetables perform well at about pH 6.5, but testing is always better than assuming.
What it is
Acid soil has a pH below 7, neutral soil is pH 7, and alkaline soil has a pH above 7. Parent rock, rainfall, previous liming and organic matter all influence the result. Soil pH does not measure fertility on its own: a nutrient-rich soil can still have an unsuitable pH for a particular crop. At very high or low pH, some nutrients become less available, causing poor growth or leaf yellowing. Chalky soils are commonly alkaline, while peaty soils are often acid. Different areas of one garden can give different readings.
What to do
Use a simple soil pH kit on several samples from each bed, following the kit instructions and recording the results. Test again after major changes, but do not chase tiny variations. If acid soil needs raising for vegetables or brassicas, apply ground limestone or chalk only at an appropriate time and at the rate stated by a reliable product label or the RHS. Do not lime alkaline or chalky soil. To manage strongly alkaline ground, improve it with organic matter and choose suitable plants rather than trying to transform it. Keep lime separate in timing from well-rotted manure applications.
Tips
Test before liming, because unnecessary lime can create nutrient problems. Most vegetables favour around pH 6.5, but potatoes prefer slightly more acid conditions and brassicas tolerate more alkaline soil. Sample cleanly from several points, avoiding recent fertiliser or lime patches. Recheck pH every few years rather than treating it as permanent.
Soil pH: frequently asked questions
What is soil ph?
Acid soil has a pH below 7, neutral soil is pH 7, and alkaline soil has a pH above 7.
How do I improve soil ph?
Use a simple soil pH kit on several samples from each bed, following the kit instructions and recording the results.
What are some tips for soil ph?
Test before liming, because unnecessary lime can create nutrient problems.
General guidance for UK gardens and allotments. Page updated 19 Sep 2026.