Garden shrubs – Hydrangea

Mophead hydrangeas – the ones large rounded heads of large flowers – originated in Japan, where they had been grown for hundreds of years, but when they reached Europe in the eighteenth century they were initially treated as tender and grown indoors – although today we assume they are hardy and grow them all outdoors. A proliferation of new varieties with improved colour began over a century ago and there’s now a such a bewildering choice that even hydrangea experts can't always tell them apart.

The odd thing about hydrangeas is that soil type determines flower colour – an acid soil will deliver blue flowers, a more alkali one will give pink or cream. Children are fascinated by this and it’s a good horticultural experiment to plant two shrubs in different soils to demonstrate this to them. If you want to generate blue flowers, you can buy a ‘blueing’ compound composed of aluminium sulphate but if your soil is highly alkali, this will not give rich colour, so instead pick a compact variety and plant it in a large container filled with lime-free compost and supplement its liquid feed with a blueing compound.

Most hydrangeas prefer dappled shade against a north or west facing wall because too bright a sun aspect will make them scorch and the large-leaved shoots need plenty of moisture during the summer which can be transpired away by too much heat and sunshine. Apply a mulch to drier soils to lock in moisture and promote good sized flowers. Pruning isn't essential but can be done each spring as new shoots appear. With established plants, remove one-third of the older, less productive stems and cut back old flowering stems to a strong pair of buds. On the other hand, remember to leave old flower-heads on through the winter to provide frost protection to the new year’s growth.

Hydrangea photograph by ghindo, used under a creative commons attribution licence

 

© blueworldgardener.co.uk