Choose the ‘right place’ – The key to successful Hydrangea cultivation is choosing the ideal place. Hydrangeas will live for many years so choose the right place to avoid the problem of trying to move them when they are large. Consider their ultimate size after five years. Size varies by cultivar but some H. macrophyllas and H. arborescens can grow to 4m (14ft). The climbing hydrangeas, H. petiolaris and H. integrifolia can cover a long fence or even the side of a house. H. arborescens also has a habit of suckering and can spread substantially if not checked.
Sun or shade – Most hydrangeas prefer partial shade with one exception:
H. paniculata will do well in full sun.
Soil – Hydrangeas will grow in almost any soil but will grow better in well-drained soil that has plenty of organic matter added.
Soil additives – Not all plants respond vigorously to fertilisers or other additives, but hydrangeas do. Adding fertilisers can significantly change the growth of the plant, making leaves larger and greener. Follow the instructions on the packet as adding too much of anything can damage the plant. Adding lime, to change the flower colour to red or pink, for example, can promote chlorosis in the leaves if added in excess.
Planting – You only plant a hydrangea once and it could then remain in the same spot for 25 years. So, plant it well. Whatever you spend on purchasing the plant, spend twice as much on the hole. I use a mixture of Sea Soil™ and a premium potting compost with added Perlite™ and a slow-release fertiliser. Also add aluminium sulphate or lime (see below) if you want to influence the flower colour.
Flower colour – It is a commonly known fact that hydrangea flowers can change colour depending on the acidity of the soil. But to be precise, this is only true of cultivars of H. macrophylla and H. m. ssp. serrata; and not all cultivars of these two species will change colour, only some. Generally, white flowering cultivars will not change colour. Also, strictly speaking, it is not the acidity of soil that causes this change, it is the availability of aluminium ions in the soil (and acid soil makes aluminium ions more available). Adding aluminium sulphate to the soil will tend to change the flower colour to blue whereas adding lime (making the soil more alkaline) will enhance pinks and reds.