The root of 3

... out

These three make a striking contrast of colour and form from spring to autumn.

Cotinus coggyria "Royal Purple" is a shrub with everything - good shape, fine foliage, brilliant autumn colour and clouds of hazy flower plumes that smother its branches and give rise to its common name of Smoke Bush. There are a number of purple-leaved forms and all would work here. Pick your own favourite.

Royal Purple has rich, wine-purple leaves which seem translucent if you can place the sun at their back. Left alone it can reach 15ft and more. In most gardens, and for this scheme, it is best to chop back some branches each spring. But not them all, for this bush flowers on older wood.

It can be tempting to go for dramatic effects by growing golden-leaved forms of shrubs like the Elder or Mexican Orange Blossom alongside your purple Smoke Bush, but think hard before you do. It may result in a striking contrast that's not too easy on the eye.

However, for one of the spurges, Euphorbia griffithii "Fireglow", the Smoke Bush provides the perfect foil. The genus Euphorbia is enormous - 2,000 species in all - and you must have this one. An herbaceous perennial from the Himalayas, its leafy stems reach 2-3 ft high, are clothed with dark green leaves and topped by orange-red bracts in early summer. It spreads underground, and will often emerge some feet from where you planted it, to form rounded hummocks.

All Euphorbias are mildly poisonous - but so are many garden plants. They also contain milky juice which bleeds from the leaves and stem if they are broken. It can be an irritant, so wear gloves.

The final plant in this grouping, Eryngium giganteum - one of the Sea Hollies - is commonly known as Miss Willmott's Ghost. Legend has it that the gardener Ellen Willmott scattered seeds of the plant as she made her way round other people's gardens.

Most of the Sea Hollies come up year after year, but this one dies after flowering. Fear not. If it's happy in your garden it will scatter seeds in abundance, without the aid of Miss Willmott, and you'll never be without it.

The sturdy stems of this spiky leaved plant reach 3-4ft tall and bear long-lasting, thistle-like, blue-green flower cones, each surrounded by a spiny silvery-white collar, stunning against a backdrop of purple Smoke Bush.

Like its companions in this trio it prefers a place in the sun and soil that's not too rich.

John the gardener