The first of my Camellias has just burst into flower and it looks like being a good year with all the Camellias that I have seen having plenty of fat flower buds. Plants such as Camellia, Rhododendron, Azalea and Acers are ‘ericaceous’ and are often described as acid-loving plants. But I garden on a neutral clay soil so why do my Camellias, Rhodos and Acers thrive? Well in fact, it is more accurate to say that these plants do not prosper in an alkaline soil, they are perfectly happy in a neutral soil if a fertiliser containing extra iron is added. Here is the explanation: ericaceous plants cannot tolerate an excess of calcium and calcium is the main cause of an alkaline soil usually in the form of chalk or limestone. Calcium reacts chemically to tie up the iron present in the soil making it unavailable to plant roots and ericaceous plant families are especially susceptible to an iron deficiency. This limits the formation of chlorophyll that gives the green colour and is vital for photosynthesis and the leaves turn a sickly yellow colour: at least this makes the problem easy to spot!
Happily the condition can be reversed by supplying a form of iron that does not react with the calcium and so remains in the soil accessible to the roots. It is usually labelled chelated or sequestered iron. Adding plenty of well-rotted organic matter to a clay soil has a slightly acidifying effect too. Of course, if you garden over chalk then these plants are not a good choice as there is simply an endless supply of calcium in the soil that you cannot counteract and you are better to choose a shrub that is suited to your conditions.
In the meantime, take advantage of the spring weather to visit an open garden with a collection of these stunning, ericaceous flowering shrubs.
Happy Gardening, Alison