Acid soil

Acid soil has a pH of below 7 and is generally high in nitrogen. It is sometimes known as an ericaceous soil or peat soil.

The pH of a soil refers to the acidity of the soil (for a further explanation of pH, click here).

Some plants only thrive in an acid soil, for example, blueberries.  Many popular spring flowering shrubs such as azaleas and magnolia also prefer an acid soil. They are healthier and give a more impressive floral display when planted in the correct acid soil.

One later flowering shrub which changes the colour of its blooms from pink to blue when you plant it in an acid soil is the hydrangea; why that happens is explored in our Hydrangea blog.

It may be possible to make your soil more acidic. This is easier if you already have an acid soil and need it to be more acidic.

Peat uplands have been over farmed and are at risk, so using peat to increase the acidity of your soil is no longer acceptable; it takes thousands of years to replace the peat bogs.

It is possible to reconcile peat free gardening and acid loving plants – see our Plews Potting Shed blog on Peat free compost alternatives.

There are other acidifying materials that you can use – although it should be pointed out that altering your garden soil’s pH is not the easy option.

To acidify your soil, you can apply:

  • Sulphur
  • Aluminium sulphate
  • Ferrous sulphate (sulphate of iron)

Each of these will need to be applied at a particular depth and in sufficient quantities.
They have an effect on the plants’ ability to take up essential nutrients. So you may decide it’s easier to grow your acid loving plants in large pots!

azaleas, scotney castle, marie shallcross, kent, national trust garden


Chartered Institute of Horticulture