RHODODENDRONS and azaleas produce a stunning splash of colour at this time of year and, if you want to get spectacular results, it helps to know a little about the right conditions for these ericaceous, sometimes called acid-loving, plants.

What is acid soil?

You probably know that acidity is measured on the pH scale, where a reading of 7 indicates neutral, less than 7 indicates acidic and over 7 indicates alkaline. Most plants grow well in soil when the pH is 6.5 to 7, but plants that thrive when the pH is lower – in the range 4.5 to 6 – are classed as ericaceous plants.

How does soil become acidic?

There are a number of natural processes which influence soil acidity. For example, soil is naturally acidic where there is a lot of organic matter breaking down, such as in peat bogs and woodlands.

Acid rain, created when moisture in the atmosphere combines with carbon dioxide to form a mild acid, naturally impacts on the pH of the soil. And in areas of high rainfall, there is the additional impact of nutrients being leached from the soil, further increasing acidification.

Is your soil acidic?

Soil pH can vary locally and, although East Lothian is predominantly in the neutral range, pockets of acidic soil will occur.

Acidity reduces the availability of certain nutrients in the soil and, whilst ericaceous plants have developed to tolerate those conditions, the growth of non-ericaceous plants will be disappointing if your soil is acidic.

Testing for pH is very simple and test kits are available in most good garden centres. The tests are inexpensive and knowing the pH of your garden soil lets you decide what plants are most appropriate for the conditions.

Don’t be concerned if you find that your soil is acidic – you only need to visit some of Scotland’s amazing west coast gardens to see that you can create wonderful gardens with ericaceous plants.

If your soil isn’t acidic but you’d like to some ericaceous plants, you can successfully grow them in containers or defined areas using ericaceous compost and fertilisers.

Our favourite acid-loving plants

Favourites amongst early-flowering ericaceous shrubs are the magnolia and the camellia.

The camellia produces fabulous blooms in late winter to early spring and, being evergreen, its dark green, glossy leaves are a welcome addition to the garden throughout the year.

Varieties of magnolia grown in the UK are generally deciduous and in spring they produce magnificent flowers before there’s much foliage, meaning that the blooms are easy to see and enjoy.

The majority of rhododendrons and azaleas bloom mid to late spring depending on variety. Botanically, rhododendron is the genus and azaleas are a group within that genus. In very general terms, rhododendrons are evergreen and tend to be larger plants with fewer, stouter stems and larger flowers, whilst azaleas are often deciduous with more, finer stems and blooms. As always, there are exceptions – the Japanese azalea is evergreen and there are also many dwarf rhododendron varieties available. It’s easy to see why they’re often confused!

Pieris are a group of small to medium evergreen ericaceous shrubs, adding all-year-round interest to your garden with colourful young foliage. Primarily grown for their foliage, they do also produce delicate clusters of small pale pink or white lantern-shaped flowers in spring and they’re sometimes known as ‘Lily of the Valley’ plants because their blooms are similar.

One of our favourite varieties is Pieris Mountain Fire with its dazzling, flame-coloured young foliage.

It’s not possible to talk about ericaceous plants without mentioning heaths and heathers. The typical Scottish mountain heather is a calluna while heaths, found in more southerly regions, are ericas. Although there are botanical differences between callunas and ericas, both tend to be known generally as heathers.

Both are mountain plants and will tolerate windy conditions and poor, rocky soil provided it is acidic. Ericas are generally more colourful but less hardy than the rugged calluna simply because of their habitat of origin. These low-growing plants require little maintenance and, with careful planning, you can create a heather garden that provides successive colour over many months.

We hope that this has given you an introduction to the world of ericaceous plants, but, of course, there are too many wonderful varieties to mention in this column. If you would like more information, why not pop in and have a chat with our plant team? They are always delighted to chat gardening!

Visit www.merryhatton.co.uk for more information.