Ericaceous compost

If your soil is alkaline (with a pH of above seven), you can grow acid-loving plants in pots or raised beds, using ericaceous potting compost. Using the right potting compost is key to success when growing plants in restricted spaces like containers or raised beds, because they need a good foundation to perform at their best from a small rooting area.

Why do plants need ericaceous compost?

Certain plants that have evolved from woodland, mountainside or heathland, require soil that's acid or neutral as they cannot absorb some nutrients in alkaline or limy soil. These plants belong to the family Ericaceae, hence the term 'ericaceous'. Plants grown on the wrong soil type soon show signs of nutrient deficiency, particularly a lack of iron and other trace elements. The key symptom is yellowing leaves, known as ‘lime-induced chlorosis’. This weakens growth and leads to poor performance.

Which plants need ericaceous compost?

The largest groups of lime-hating or acid-loving plants are rhododendrons (including azaleas), camellias and pieris. Blueberries do best in ericaceous compost, along with summer-flowering heather (Calluna), Fothergilla, Gardenia, Gaultheria, Kalmia and Leucothoe.

What's in ericaceous compost?

Until recently, many potting composts, particularly ericaceous compost, have had peat as their main ingredient. Peat is naturally acidic, however growing awareness of the environmental degradation caused by peat extraction has led to the development of many excellent peat-free alternatives. Peat is mainly harvested from lowland bogs in the UK and Europe. Peat bogs hold vast amounts of carbon and water, and provide a habitat for many rare species of wildlife. Destroying them to extract peat therefore exacerbates climate change, puts wildlife at risk and increases the risk of localised flooding. There are plans to phase out the use of peat in horticulture and composts, but progress is slow.

There are a few peat-free ericaceous composts available, with ingredients such as composted bracken or bark, coir (coconut fibre) and wool. You can also buy a compost called Moorland Gold which is made using reclaimed peat, which has been washed into lakes and reservoirs.

How to make ericaceous compost

Certain materials have a high acidic content and can be composted, such as deciduous leaves, conifer needles, Christmas trees (put through a shredder), bracken and coffee grounds. These can be mixed in with acid topsoil or sharp sand, plus some grit or perlite, to make compost. However, it's hard to achieve a reliable and consistent ericaceous compost mix for using in pots so there's always the risk that plants will fail to thrive.