Plant Of The Month - August - Hydrangea

Hydrangeas have large blooms that bring flamboyant colour to the garden in late summer and autumn. They are easy to grow, dependable and improve with age.  Use them in big, bold groups in the border, or even try them in large containers. 

HTA’s David Gilchrist comments “Hydrangeas are deciduous and can be either treated as large shrubs or small trees. They are grown for their beautifully domed or flattened flowers which appear from late summer for about a month. 

The flowers normally consist of a mass of fertile flowers surrounded by infertile flowers which give the hydrangea its large flower heads. Hydrangeas are recommended for the amateur and the experienced gardener alike.”

Nominated and agreed upon by HTA member growers and retailers, the HTA’s Plant of the Month campaign highlights the plants that are widely available and looking especially good in garden centres each month. Different varieties are recommended together with simple planting and care hints and tips.

Mop head hydrangeas (with rounded heads of large flowers) come from Japan where the native species with lace cap flowers (flattened heads of large flowers) have been grown for hundreds of years. When these plants reached the west in the eighteenth century they caused a sensation, initially treated as tender and grown indoors. There are now many, many varieties to choose from. 

Soils for Colour

With Hydrangeas, the soil type determines the colour. Acid soils for example produce blue flowers. To create blue flowers on a chalky soil, use a blueing compound composed of aluminium sulphate. This can be purchased at your local garden centre. However, the results won’t compare with plants growing in a naturally acid soil. 

Alternatively, you could grow a compact variety such as ‘Blue Bird’ in a large container filled with ericeous compost and supplement its liquid feed with a blueing compound. 

Site and Watering

Hydrangeas are true survivors and can be often seen flowering in overgrown and neglected gardens. Mop heads and Lace Caps prefer dappled shade against a north or west facing wall. If it is too bright they are likely to scorch. Their leafy shoots need plenty of moisture during the summer, apply a mulch of well-rotted compost to drier soils to help lock in moisture and promote decent sized flowers. Plants also need to be sheltered from cold winds which can scorch new foliage during the spring.

Pruning

Pruning isn’t essential but can be done each spring as new shoots appear.  With established plants, just remove one third of the older, less productive stems and cut back old flowering stems to a strong pair of buds. 

Leave old flower heads on over winter to provide frost protection for new growth. The brown papery domes look great when covered with hoar frost.

Left un-pruned Hydrangeas will continue to bloom but the size of the flower heads will be reduced by the overcrowded stems. Hydrangea paniculata types need to be cut back completely each spring.