Join the RHS today and support our charitable work
Keep track of your plants with reminders & care tips – all to help you grow successfully
RHS members get reduced ticket prices
RHS members get free access to RHS Gardens
Free entry to RHS members at selected times »
Reduced prices on RHS Garden courses and workshops
020 3176 5800
Mon – Fri | 9am – 5pm
Help us achieve our goals
Join the RHS today and support our charity
When designing and planting your garden, you need to know whether the soil is acid or alkaline, as different plants thrive in different soils. The soil pH is a number that describes how acid or alkaline your soil is. A pH of 7.0 is considered neutral. An acid soil has a pH value below 7.0 and above 7.0 the soil is alkaline.
Soil pH colour chart
It is especially worth checking soil pH before designing or planting a new garden, making vegetable plots, planting fruit, when growth is disappointing, or where yellowing of foliage occurs.
Lime is added to increase soil pH (make it more alkaline) and acidifying materials are added to decrease soil pH.
Testing can be done at any time, but if carried out within three months of adding lime, fertiliser or organic matter, the test may give misleading results.
Professional testing: RHS soil analysis service provides a full written report.
Home testing: You can test your soil pH yourself using a DIY kit widely available at garden centres. These kits are relatively cheap and easy to use and give a good indication of soil pH. But for the best results, send a soil sample to a laboratory for detailed analysis.
Always follow the sampling directions given by the test kit or laboratory to get a representative sample for the area in question.
Laboratory tests also detect free calcium carbonate (chalk or limestone). This may not be measured by DIY kits. A quick home test to check for free calcium carbonate is to add vinegar to a soil sample. If ‘fizzing’ is seen, free calcium carbonate is present.
A pH test measures soil acidity or alkalinity. A pH 7.0 is considered neutral. An acid soil has a pH value below 7.0. Above pH 7.0 the soil is alkaline.
Certain plant diseases such as club root and nutrient deficiencies can be associated with acid or alkaline soil conditions.
Acidifying soilAgricultural Lime AssociationChalky soilChalky soil: plants forClay soilClay soil: plants forHardy heathersLime and limingPotash Development Association RHS soil analysis serviceSoil cultivationSoil types
the RHS today and get 12 months for the price of 9
RHS members can get exclusive individual advice from the RHS Gardening Advice team.
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.