Soil pH levels may vary throughout your garden and this soil testing kit will help you to decide which of your plants and vegetables suit which areas. When designing and planning your kitchen garden or allotment it helps to know if your soil is acid or alkaline as different crops 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.

There are many reasons why you need to be aware of your soil’s acid/alkaline balance.  The solubility of minerals can be compromised if there is an imbalanced pH.  Minerals become locked-up in the soil making them unavailable for plants to absorb.  Essential and valuable micro-organisms become less active in the soil (earthworms hate acid conditions) and certain pests will be active at specific levels like the bane of brassicas, Club Root, a fungal disease which thrives in acidic soil. 

Most vegetables and fruit grow very healthy in a neutral to slightly acid pH, the ideal being around 6.5.  There are exceptions like the acid-loving blueberry and the leafy brassicas that thrive in a more alkaline soil. Be aware before you sow or plant of the specific soil pH requirements of the crop or family of vegetable types that you are planting as cultivating the area to a specific soil pH may be necessary.

Most fruit and vegetables will grow in a pH of between ph 5.5-7.5 but achieving the optimum growing conditions will ensure healthier growing conditions for your crops. You can test your soil pH yourself using a Soil Testing Kit which is easy to use and relatively inexpensive. 

For more detailed results, the RHS (Royal Horticultural Society) offers a Soil Analysis Service which has been developed specifically with gardeners in mind, providing an analysis of soil texture, pH, organic matter and three major plant nutrients (Potassium, Phosphorus & Magnesium).

pH Reading Your Results

Soil pH Grid

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 nutrients being available to plants.
  • Action: Add lime to raise the pH to above 5.0. The addition of garden 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.
  • One advantage of this pH level is that clubroot disease of cabbage family crops (brassicas) is reduced so you will be able to grow lots of Brassicas!
  • Action: Add plenty of compost and manure annually, 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.  Consider raised beds with an improved top soil added.