Ericaceous plants are plants that don’t like growing in soils that contain lime. They are also known as acid lovers or lime haters. This means they won’t grow well in soils that have a high pH - such soils are referred to as alkaline.
Ericaceous plants include Rhododendron, Camellia, Azalea, Pieris, summer-flowering heathers (calluna) and even Japanese maples (Acer) among others. This also applies to Blueberries.
If you try to grow ericaceous plants in alkaline or limey soils, they produce yellow leaves. This is a condition known as lime-induced chlorosis, where they don’t grow or flower well and usually, finally die.
The main reason for this is that they need plenty of iron and other soil nutrients that become insoluble or ‘locked up’ in the soil at high pH, so the plants can’t absorb them.
If your soil is alkaline, you could try digging a large hole, lining it with plastic sheeting, making some drainage holes in the plastic, and then filling with a lime-free soil or ericaceous compost. However, this rarely works well and is a bit of a risk.
It is much better and easier to grow ericaceous plants in large pots filled with ericaceous (lime free) compost. Growing ericaceous plants in containers also allows you to grow them in the right place in the garden. Most of the plants listed (apart from calluna and blueberries) prefer a position in light shade or out of direct sunlight - especially early morning sunlight, which can cause the flower buds and flowers to turn brown and drop off.
The other thing you need to ensure for fabulous, healthy growth is to feed the plants with a suitable fertiliser. Whereas many plants can be fed with a general-purpose feed, ericaceous plants really do much better if fed with a specific ericaceous plant feed. These contain all the specific nutrients needed for great green leaves and masses of fabulous flowers.
This can either be a granular feed or a liquid feed - whichever you prefer. Continuous release feeds are perfect for those who lack time to feed regularly as they feed for up to 6 months from 1 application. Liquid feeds are more suited to those who love the routine of regular feeding.
Because Rhododendrons, Azaleas and Camellias set their flower buds from June to August, it is essential to keep them well fed during this period, as well as feeding in spring.
Because most ericaceous plants - especially rhododendrons, azaleas, camellias and heathers - are shallow rooted, they are prone to drying out during prolonged dry periods. So it is very important to keep the soil or compost moist. This is particularly important during the flower bud setting period in summer; if the soil or compost is allowed to dry out at this time bud set can fail. So water plants weekly during dry periods and mulch the soil well to preserve moisture.
Plants, like rhododendrons, are classed as ericaceous and have to be in completely ericaceous soil. Others are acid loving and prefer to grow in an acidic soil but can tolerate a slightly more alkaline soil than ericaceous plants.