Do You Know Your Soil’s PH Value?

PH Soil Test

Soil pH testing 

When you are designing your garden, it is really important to know what soil type you will be planting into and the pH of your soil. If you have alkaline soil, you won’t be able to grow blue hydrangeas, for example.

What is soil? 

“The upper layer of earth in which plants grow, a black or dark brown material typically consisting of a mixture of organic remains, clay and rock particles”

Oxford Dictionary


There is also a mix of water, nutrients, and air in the soil and this is what the growing plants are relying on to survive.


Home soil pH testing

When someone is talking about the pH of the soil, they are referring to whether it is acid or alkaline. This is measured and listed on a scale of 1 to 14. You can test your soil’s pH at any time of the year. If you have previously added lime or compost to your soil, you should wait at least 3 months before testing the soil. 

Most, if not all, garden centres will sell simple soil pH testing kits. While a pH result is by number, these basic kits will generally give a colour result. Yellow to orange indicates an acidic soil, green indicates neutral, and the darker the green result will indicate how alkaline the soil it. 

Professional soil pH testing

If you are looking for more answers than just roughly what pH your soil is, then there are professional laboratories that can carry out more detailed investigations for you. The RHS offers a Soil Analysis Service and issues a full written report on the findings. Professional testing will also look to see what other components are in the soil sample that you send. A common additional test is one for calcium carbonate, otherwise known as chalk or limestone. You can check this at home very easily – if your soil sample fizzes when you add vinegar to it, there is calcium carbonate in your soil sample. 

Soil pH results:

  • Acid soil: a pH of below 7
  • Neutral: a pH of 7
  • Alkaline soil: a pH over 7

As well as in the design stages, it is particularly worthwhile to check your soil’s pH if you are experiencing plant growth that is below the expected range, or if the plant’s foliage is yellow. 


What to do with the results

So you’ve tested the soil and you know what it’s pH is, but what does that mean for your garden and what so you need to do about it – it anything? 

Soil pH of 3.0 – 5.0

This range of pH indicates that your soil is very acidic. Acidic soils are very often lacking in the trace elements that are vital to plant health and growth. One of the other main issues with a highly acidic soil is that bacteria are unable to rot organic waste.

  • Apply lime to the soil, aiming to raise the soil pH to above 5.


Soil pH of 5.1 – 6.0

This range of pH indicates that your soil is acid, but at this level it is perfect for ericaceous plants. Camellias, heather, and rhododendrons should thrive in your garden

  • Apply lime to areas that you want to grow other plants in

Soil pH of 6.1 – 7.0

While this range is still defined as a moderately acid soil, a pH of 6.5 is considered to be the best all round soil pH for gardens. This is the optimum soil pH for nutrients and earthworms.

  • No action is generally required with the soil pH in this range 

Soil pH of 7.1 – 8.0

In this range, the soil is referred to as alkaline and iron, phosphorus, and manganese availability is reduced.

  • Apply treatments such as iron sulphate and sulphur to increase the levels of acid in the soil. A soil pH over 8.0 may prove to be untreatable.


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7 Replies to “Do You Know Your Soil’s PH Value?”

  1. What PH is best for growing heather?

  2. As a rule of thumb, winter and spring flowering varieties are suitable for alkaline soil and those that flower in the summer need more acidic soil

    1. Take a look at this website HEATHER

  3. Maybe this explains the colour of my hydrangeas!?

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