Heather soil: how to use it well in the garden?

What is heather soil?

Under the term “heather soil”, two quite different substrates are found :

• the true heather soil,
• the so-called heather soil.

The true heather soil

True heather soil occurs naturally in woodland understoreys, on sandy soil, at the foot of conifers or in heathland. This soil is formed mainly by decomposition of heather, an organic matter poor in nutrients. Heather soil is very acidic (pH < 5), nitrogen and phosphorus are scarcely available and there is often evidence of pollutants or heavy metals such as aluminium ions. As this soil is now only exploited on a very small scale in Sologne (France), it is rare and therefore expensive.

The so-called “heather soil”

It is an ‘imitation’ of true heather soil. It is a compound of siliceous soil, a little sand for permeability, bark and pine needles ground to a powder, plant fibres, compost and sometimes turf. In some cases, fertiliser is also included in this potting compost.

please note : turf moors are very fragile acidic natural mediums where a particularly distinctive flora and fauna live. Exploitation of these turf moors almost irreparably destroys them because it takes thousands of years for them to reconstitute. So avoid commercial “so-called heather soils” that contain blond turf.

Disadvantages of heather soil

Gardeners are generally well-meaning. If they read “ericaceous plant”, they plant in pure heather soil. Unfortunately, nothing is more effective at killing a plant, even an ‘ericaceous’ one! It is actually one of the main causes of failure when growing plants in acidic medium.

Why? Because real heather soil should never be used pure!

In reality, this substrate has the drawbacks of its qualities:

• High acidity: hooray, great! It is acidic so it is good for acidophilous plants. True, but not to the point of planting directly in this very acidic substrate. Excessive acidification of soil will reduce activity of soil fauna and thus limit availability of nutrients. Soil fauna is fauna of the soil (worms, invertebrates, springtails and even bacteria) that helps create soil and mineralise organic matter, thereby feeding plants.
• Rich in humus but… poor in nutrients: this soil results from decomposition of heathers. Furthermore, the little that is present is difficult to assimilate (see above).
• It does not retain water: due to its composition, it is a very permeable soil. This is an advantage because ericaceous plants prefer well-drained soils, especially in winter, but… once dry, this substrate is almost impossible to re-wet, bringing death and desolation to your beloved plants.
• It warms up quickly in spring: this can sometimes cause problems for certain acidophilous plants that flower early in season. They can then be caught by a late frost that aborts flowering.

Planting in pure heather soil is one of main causes of failure in the garden; if you are looking for the other nine, read our article : “10 ways to kill a plant naturally“

How can I better use heather soil, and what could I use instead?

When planting

Heather soil and substrate called heather soil are used to increase soil acidity and improve drainage.

• Genuine heather soil

Genuine heather soil must never be used pure! It should be used at no more than 30%: minimum 1/3 heather soil to 2/3 topsoil.

But, to establish acidophilous plants, best practice remains to prepare a mix of:

1/4 heather soil + 1/4 leaf mould + 1/4 topsoil + 1/4 free-draining substrate such as gravel, sand or pumice.

• So-called heather soil

With so-called heather soil: mix it with your garden soil at a rate of 50% so-called heather soil to 50% topsoil. You can, if necessary, use so-called heather soil pure only for container plantings. But do not forget watering!

If you do not have heather soil or so-called heather soil, replace it with:

• pine needles and pine bark: soil under conifers is often very acidic because it results from accumulation of needles. You can therefore add a surface layer of some pine needles. You can also add some pieces of decomposing bark.
• leaf mould: this is the result of fermentation and decomposition of leaves. This leaf mould is a more acidic substrate than conventional compost. Best leaves to use are oak and chestnut. To make it, store leaves in a wire silo and aerate from time to time by turning with a fork.

And of course, you can use fallen leaves and pine needles as mulch. This will keep the base of your bushes cool and moist, while enriching the soil and maintaining some acidity.

Find out more...

Planting ericaceous plants isn’t so complicated if you follow Michael’s good advice. He also gives you 5 tips to help you succeed with ericaceous bushes.

With all that, you’ll undoubtedly want to start planting acidophilous plants. The most beautiful plants in this category can be found in our online nursery: ericaceous bushes.