Ericaceous compost
All you need to know about ericaceous compost, and where to buy it.
Ericaceous compost is acidic, with a pH of between four and five. It's suitable for growing ericaceous or acid-loving plants, which need a growing medium that's free from lime (alkalinity), such as blueberries and rhododendrons. Acidity and alkalinity are measured by the pH (potential Hydrogen) scale, and you can find out the pH of your soil using a cheap and simple test kit.
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.
Advice on buying ericaceous compost
- Ericaceous compost can be bought from garden centres, nurseries, retail DIY stores, and direct from the manufacturer by mail order. At present most composts are sold in plastic sacks apart from Melcourt SylvaGrow compost, which has an excellent refillable 'bag for life' scheme
- To avoid buying peat-based composts, look for products described as 'peat free'. Some well-known brands don't mention on the packaging that their products contain peat
Where to buy ericaceous compost
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.
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