Cool looking shady customers

These hot and dry days of summer, it is good to have some indicator plants that let you know when some H2O is needed - and few plants do that as effectively as hydrangeas. Once they have been in moisture deficiency for a day or two, they hang their flower heads, a sure-fire indicator you need to get the hoses out.

The popularity of these summer blooming stalwarts has waxed and waned over the years. Once popular here , they fell from grace a little, with a generation of gardeners regarding them as common, but seem to be having a bit of a revival, perhaps spurred by the arrival of new varieties, and the uptake of gardening by a younger generation.

Older gardeners will recall when all gardens had a dollop of hydrangeas, often planted on a south-facing wall. They would provide green foliage throughout the growing season and, as long as they were not butchered too badly at pruning time, would usually furnish a nice display of flowers over the summer. My first garden had such a row of hydrangeas, awaiting my first pruning, then failing to flower for a couple of years as I pruned too hard and injudiciously.

My clearest recollection of those hydrangeas is the role they played in my first attempts of growing plants from cuttings. I took slips from several different rock plants I had in another border, and lined them out in freshly-turned garden soil, using hydrangea trimmings to mark the end of the rows. The inevitable happened - the only cuttings that struck were the hydrangeas.

All these were the most common form of hydrangea, "mop heads". This slightly disrespectful epithet denotes that the flower heads are entirely composed of sterile flowers, with much larger florets than the fertile flowers. These flowers can look a little heavy and, indeed, can be more than a little weighty, especially after a shower of rain.

The lacecap types, which have a mix of fertile and sterile flowers, probably should be more widely grown as they are as easily grown as mop tops, but easier to mix with other flowers as the flower head is looser, more graceful and more subtle in its effect. Often it is composed of a ring of sterile flowers around a central core of fertile ones.

The common garden hydrangeas as referred to is H. macrophylla and, as I said before, there has been an interesting range of new forms coming on to the market in the past few years.

I have been impressed by the picotee-edged form called "Sensation". This is a vigorous growing mop top with bright green glossy leaves and masses of large flower heads with the coolest flowers of rose-pink edged with white. The new buds are greenish and an opening head has the most amazing combination of colours.

The new You-Me series is even more interesting, with a range of pastel colours in double forms, quite unlike anything grandma grew in her garden. "You-Me Forever" has intriguing balls of double blue blossom while "You-Me Eternity" has the same form but in dark pink. These are fabulous plants and worth seeking out in your garden centre.

If you are interested in lacecaps "Nightingale" is an older variety, but is as nice as any, with light blue sterile flowers around the edge of medium-sized flowers on a robust plant.

Of course, there are many other kinds of hydrangeas, apart from the H. macrophylla types. "Annabelle" is a stunning form of a more unusual species, H. arborescens. As the name suggests this species is larger than the usual species, but nonetheless is an amazing shrub with a bushy but rather untidy habit. It bears large cream flower heads throughout the summer. This is one that will quickly let you know if it is too dry so make sure you keep it well watered and mulched - it would probably do best in light shade.

The American species H. paniculata is most often represented by its cultivar "Grandiflora" in New Zealand. This forms a strong-growing multi-stemmed large shrub which is covered with large panicles, up to 30cm long, of creamy-white flowers in summer. These flowers turn pink with age. The plant is vigorous and needs a little space to be seen at its best, but is a spectacular sight when well grown - it does best in light shade in dry conditions.

In a way, this plant (nicknamed "Pee Gee" in America, after its initials) is the "mop top" version of the species. If you are looking for a lacecap version you should go for "Tardiva" which has the usual mix of fertile and sterile flowers, the sterile flowers being white when young but ageing to pink. With both the varieties, a severe pruning in the spring helps to promote good flowering, as does thinning out crowded stems in late winter.

A real pet for the shaded garden is H. aspersa "Villosa", a willowy shrub that grows perhaps 2.5 metres high and has flattened lacecap blooms, which consist of tiny purplish-blue fertile flowers surrounded by large white or lilac-tinged sterile flowers which bees enjoy visiting. The sterile flowers are carried on little stems and will flutter on a windy day, giving the effect of hundreds of lilac butterflies. One to treasure.