It is especially worth checking soil

This describes how acid or alkaline soil is, and is expressed as a number between 0 and 14. Soil with a pH of 7 is neutral, an acid soil has a lower value, and an alkaline soil has a higher one. Most plants grow best in soil that’s within a specific pH range, so it’s useful to know your soil’s pH. Testing kits are easy to use and widely available in garden centres and online.

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

This describes how acid or alkaline soil is, and is expressed as a number between 0 and 14. Soil with a pH of 7 is neutral, an acid soil has a lower value, and an alkaline soil has a higher one. Most plants grow best in soil that’s within a specific pH range, so it’s useful to know your soil’s pH. Testing kits are easy to use and widely available in garden centres and online.

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.

Interpreting the results of a soil pH test

A pH test measures soil acidity or alkalinity. A pH 7.0 is considered neutral. An

The acidity/alkalinity of soil is measured on a pH scale, which runs from 0 to 14. Neutral soil has a pH of 7. Acid (or ericaceous) soil has a pH of less than 7, and the lower the pH, the more acidic the soil. You can measure your soil pH using a simple testing kit. Acid-loving (ericaceous) plants include rhododendrons, camellias, heathers and blueberries. Adding lime to soil will reduce its acidity. A slightly acidic soil of pH 6.5 is the best general-purpose pH for gardens, allowing a wide range of plants to grow.

pH 3.0 - 5.0

• Very acid soil
• Most plant nutrients, particularly calcium, potassium, magnesium and copper, become more soluble under very acid conditions and are easily washed away
• Most phosphates are locked up and unavailable to plants below pH 5.1, although some acid tolerant plants can utilise aluminium phosphate
• Acid sandy soils are often deficient in trace elements
• Bacteria cannot rot organic matter below pH 4.7 resulting in fewer
  To grow well, plants need a wide range of nutrients in various amounts, depending on the individual plant and its stage of growth. The three key plant nutrients usually derived from soil are nitrogen, phosphorus and potassium, while carbon, oxygen and hydrogen are absorbed from the air. Other vital soil nutrients include magnesium, calcium and sulphur. Most garden soils contain enough nutrients to promote healthy plant growth.

  nutrients being available to plants
• Action: Add lime to raise the pH to above 5.0. The addition of lime can help break up acid clay soils

 pH 5.1 - 6.0

• Acid soil
• Ideal for ericaceous (lime-hating) plants such as rhododendrons, camellias and heathers
• Action: Add lime if other plants are grown

pH 6.1 - 7.0

• Moderately acid soil
• A pH 6.5 is the best general purpose pH for gardens, allowing a wide range of plants to grow, except lime-hating plants
• The availability of major nutrients is at its highest and bacterial and earthworm activity is optimum at this pH
• Action: It is not usually necessary to add anything to improve soil pH at this level

pH 7.1 - 8.0

• Alkaline soil
• Phosphorus availability decreases
• Iron and manganese become less available leading to lime-induced chlorosis
• But an advantage of this pH level is that clubroot disease of cabbage family crops (brassicas) is reduced
• Action: Sulphur, iron sulphate and other acidifying agents can sometimes be added to reduce pH. Clay soils often require very large amounts of acidifying material and soils with free chalk or lime are not usually treatable

Certain plant diseases such as club root and nutrient deficiencies can be associated with acid or

The acidity/alkalinity of soil is measured on a pH scale, which runs from 0 to 14. Neutral soil has a pH of 7. Alkaline (lime-rich) soil has a pH above 7, and the higher the pH, the more alkaline the soil. Chalky or limestone soils are alkaline. You can measure your soil pH using a simple testing kit. If you have alkaline soil, choose plants that will thrive in it – acid-loving or ericaceous plants such as rhododendrons will not. Club root disease (which affects brassicas) is less prevalent in alkaline soil.