Ericaceous Compost

What is Ericaceous Compost?

You will probably have heard of ericaceous compost in terms of what you can grow in it. It is an acidic compost, and suitable for growing rhododendrons, camellias, azaleas, heathers, and other plants that dislike alkaline soil, also known as lime-hating plants. The name ‘ericaceous’ comes from the Latin name for heathers, Erica.

When to Use Acidic Compost

You use ericaceous compost when the soil in your garden is too alkaline to grow lime-haters. And how do you know the pH of your soil? Well, you can either look at your neighbours’ gardens to see if they’re growing rhododendrons, or you can buy a soil-testing kit and test the pH for yourself. If the pH is above 7.0, then you will probably need to grow your ericaceous plants in pots, and in ericaceous compost. Although you can add chemicals to increase the acidity of your soil, you probably won’t have much long-term effect, especially if your soil is very alkaline. And some plants are so strongly ericaceous that they won’t grow in even slightly alkaline soil. Rhododendrons and azaleas are more tolerant, but blueberries like a pH of less than 5.5, so need to be grown in pots in ericaceous compost in much of the UK.

Where to Buy Ericaceous Compost

Ericaceous compost is widely available from garden centres and compost suppliers. The Royal Horticultural Society recommends loam-based ericaceous compost such as John Innes Compost, but says that peat-free ericaceous composts are improving all the time, and will be perfectly suitable. 

You can grow a wide range of plants in pots, even quite large shrubs such as camellias, provided you choose the right pots. Dwarf rhododendrons, such as the Rhododendron yakushimanum hybrids, are really good pot plants. They flower reliably, year after year, and remain small. There are also some lovely dwarf azaleas available that are perfect for pot cultivation. Camellias can get a bit big, but choose carefully, and you could even have one of those. As with all pot cultivation, you need to choose a pot that is not too much bigger than the pot your plant is currently in, or the soil will go sour before the roots have spread into it. You need it to be about two inches bigger than the rootball all the way round. If you want to use a much bigger pot, then put several plants in it.

Whatever ericaceous compost you choose, your plants will need repotting every couple of years, as the compost will lose its structure and nutrients over time. This will give you a chance to move your plants into bigger pots if necessary, or prune the rootball if you want to keep them small. Your plants will also thank you for feeding them with ericaceous fertiliser in the spring when they start to grow again.