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

What is heather soil?

The term “heather soil” covers two quite different growing media:

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

True heather soil

Natural, true heather soil is found in woodland, on sandy soil, at the foot of conifers or in heathlands covered with heather. This soil is created mainly by the decomposition of heathers, organic matter that is poor in nutrients. Heather soil is highly acidic (pH < 5), nitrogen and phosphorus are not readily available, and pollutants or heavy metals such as aluminium ions are often present. As this soil is now only extracted on a very small scale in Sologne (France), it is rare and therefore expensive.

So-called “heather soil”

This is an “imitation” of true heather soil. It is composed of siliceous soil, a little sand for permeability, bark and pine needles reduced to powder, plant fibres, compost and sometimes turf. In some cases, fertiliser is also added to this “potting compost“.

Please note: turf moors are highly fragile acidic natural habitats where very distinctive flora and fauna live. Extracting from these turf moors destroys them almost irreversibly, as they take thousands of years to regenerate. So let us avoid commercial “so-called heather soils” containing blond turf.

The drawbacks of heather soil

Gardeners are generally well-meaning people. If they read “ericaceous plant”, they plant in pure, genuine heather soil. Unfortunately, it is one of the most effective ways to kill a plant, even one that is “ericaceous”! This is, in fact, one of the main reasons why growing acidophilous plants fails.

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

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

• High acidity: yippee, marvellous! It is acidic, so it is good for acidophilous plants. True, but not to the point of planting directly in this highly acidic medium. Excessive acidification of the soil will reduce soil fauna activity and therefore limit the availability of nutrients. Soil fauna comprises the animals living in the soil (worms, invertebrates, springtails and even bacteria) that help to create soil and mineralise organic matter, thereby feeding plants.
• Rich in humus but… low in nutrients: this soil comes from the decomposition of heathers. What little it contains is also difficult for plants to absorb (see above).
• It does not retain water: because of its composition, it is a highly permeable soil. This is an advantage because ericaceous plants prefer well-drained soils, especially in winter, but… once dry, this medium is almost impossible to re-wet, bringing death and desolation upon your beloved little plants.
• It warms up quickly in spring: this can sometimes cause problems for certain acidophilous plants that flower early in the season. They can then be caught out by a late frost, which prevents flowering.

Planting in pure heather soil is one of the 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 you use heather soil more effectively, and what can you replace it with?

When planting

Heather soil and so-called heather soil substrate are used to increase the acidity of soil and improve drainage.

• True heather soil

True heather soil must never be used pure! It should only make up a maximum of 30%: at least 1/3 heather soil and 2/3 good garden soil.

However, when planting acidophilous plants, the ideal mixture is:

1/4 heather soil + 1/4 leaf mould + 1/4 good garden soil + 1/4 draining “substrate” such as gravel, sand or pozzolana.

• So-called heather soil

With “so-called heather soil”: you will need to mix it with the soil in your garden, using 50% “so-called heather soil” and 50% good garden soil. If necessary, you can use pure “so-called heather soil” only when planting in pots. But do not forget to water it!

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

• pine needles and bark: soil beneath conifers is often very acidic because it results from the accumulation of needles. You can therefore add a small amount of pine needles to the surface. You can also add a few pieces of decomposing bark.
• leaf mould: this is the result of the fermentation and decomposition of leaves. This leaf mould is a more acidic substrate than conventional compost. The best leaves to use are oak and sweet chestnut leaves. To make it, you can store leaves in a mesh-sided bin, airing them from time to time by mixing them with a fork.

And of course, you can use fallen leaves and pine needles as mulch. This will keep the area around the roots of your shrubs cool and moist, while enriching the soil and maintaining a certain level of acidity.

For further information...

Planting ericaceous plants is not particularly complicated if you follow Michael’s sound advice. He also gives you 5 tips for successfully growing ericaceous shrubs.

With all this in mind, you will no doubt feel like planting acidophilous plants. The finest plants in this category can be found in our online nursery: ericaceous shrubs.