Clumber Gardener: Handsome hydrangeas are always so popular

The ‘mop head’ kinds are the most commonly seen, producing big, globe-shaped flower heads.

A well-known quirk with many hydrangea varieties is that their flower colour changes according to the soil or compost in which they are being grown.

Colour depends on the availability of aluminium, the element that traditional hydrangea ‘blueing agents’ contain.

On chalky, alkaline soils, flowers tend to be pink, on acid soil they will produce blue flowers.

This can range from sky blue to vivid gentian blue, depending on the variety. Good blues are ‘Generale Vicomtesse de Vibraye’ and ‘Marechal Foch’.

For pink, the aptly named Goliath has large flower heads while Nigra produces mainly rose-coloured florets and has characteristic black stems.

Once the flower heads have started to turn brown, they form excellent everlasting flowers.

In colder areas they are best left on the plant over

the winter.

This provides some protection to the buds immediately below which can be damaged by cold weather over the winter.

The other big group are the ‘lace cap’ kinds, which produce flattened flower heads consisting of small fertile flowers in the centre, surrounded by bigger, showy ray florets.

Two lace caps which have won the Royal Horticultural Society’s Award of Garden Merit, in recognition of their reliable performance, are Zorro, which combines dark purple to black stems with deep blue flowers on acid soils, and Love You Kiss, a Japanese introduction with white flowers which are edged pink and red.

Outside these two groups forms of Hydrangea paniculata are known for their cone-shaped flower heads.

Pink Diamond is another Annual Garden of Merit winner, producing creamy white flowers which fade to pink over a long period.

Shrubby hydrangeas can be grown in a mixed border with annuals and summer flowering perennials.

Blue campanulas and tradescantias and pink and blue geraniums make good companions.

One of my favourite blues is the willow gentian, Gentiana asclepiadea, which has intense blue flowers on gracefully arching stems.

Like the hydrangeas, it thrives in light shade.

Also good for shade is the climbing hydrangea, H. petiolaris.

It will succeed on a shady north-facing wall, producing creamy-white flowers in June and July.

It has a lower growing, variegated form, Miranda, which has heart-shaped green and gold leaves.

All hydrangeas resent dryness at the roots, so make sure they have organic matter added to improve the moisture holding ability of your soil, especially if you garden on a light sandy soil.

Well-rotted manure, mushroom compost (which contains lime, so will induce pink flowers), leaf mould, or home-made compost can all be used.

Be prepared to water hydrangeas if their roots are competing with the roots of established trees and leaves start to wilt in high summer, or if you’re tempted to buy and plant container grown plants now which are in flower and looking good.

We are now into August so it is time to sow Japanese onion varieties such as Senshyu Yellow.

These will over-winter and help fill the ‘onion gap’, cropping in late June or early July after the onions in store have been used up, but before the main crop onions sown in the spring are ready.

Keep dead-heading as this encourages plants to produce more blooms.

Dahlias and sweet peas respond well to this, as do plants in hanging baskets and containers.

Trim beech, yew and Leyland cypress hedges and propagate tender perennials such as penstemons, fuchsias, pelargoniums and osteospermums.

These root readily from non-flowering shoots.0

Visit gardens with summer bedding displays, herbaceous borders or kitchen gardens, which will all be at their best in August.

Gardens opening for the National Gardens Scheme (www.ngs.org.uk) the Royal Horticultural Society and its partner gardens (www.rhs.org.uk) and the National Trust (www.nationaltrust.org.uk) all have such gardens and many have activities for children during the long summer holiday.