10 AGM-winning plants for clay soil

Growing the right plants is a big part of successful gardening on clay soil; here are 10 winners of the prestigious RHS Award of Garden Merit that will grow better than most on clay

Gardeners who have never gardened on clay have no idea of the problems it can bring. If you’ve ever got your boot stuck in the mud on a country walk – well, just imagine a whole garden full of the stuff.

Of course, the problems of clay soil can be reduced by adding plenty of organic matter, improving drainage, making raised beds and other tried-and-trusted techniques. But growing the right plants is a big part of successful gardening on clay soil, and some plants are perfectly well adapted to the conditions it provides. So here are 10 winners of the prestigious RHS Award of Garden Merit that will grow better than most on clay.

H1 - H7 indicated the new hardiness ratings

Full details of hardiness ratings (510kB pdf)

Ajuga reptans ‘Catlin’s Giant’

‘Catlin’s Giant’ bugle succeeds on clay because bugle grows naturally on clay in the wild. It’s one of the larger varieties, with bold bronze leaves and upright spikes of rich blue flowers in spring. It makes an effective carpet, but is best split and replanted every few years. 20cm (8in). H7.

Rosa ‘Blanche Double de Coubert’

Many old-fashioned shrub roses grow well on clay soil, so ‘Blanche Double de Coubert’ is a representative of them all, as well as being one of the finest old roses in its own right. The semi-double double white flowers are blushed in bud, highly scented, open over many weeks and develop red hips later. Best left unpruned but rejuvenated occasionally by cutting back hard. 2m (6ft6in). H7.

Ribes sanguineum ‘Pulborough Scarlet’

One the most dependable and most colourful of early shrubs, the long strings of deep red flowers sway and tremble in the breeze all along the previous year’s shoots. It appreciates full sun and pruning as soon as the flowers drop, and it can also be trained in a fan on a wall, perhaps with Clematis alpina growing through it. 2m (6ft6in). H6.

Philadelphus ‘Manteau d’Hermine’

This was one of the first shrubs I ever planted and I still remember enjoying its neat growth, double pure white, early summer flowers and lovely vanilla fragrance. Its compact habit suits smaller gardens and tight spaces, and its profusion of double flowers lasts longer than those of the more common single varieties. Best in full sun and pruned immediately after flowering. 1m (3ft). H6.

Laburnum × watereri ‘Vossii’

The best of all the laburnums, and the one usually offered, ‘Vossii’ is a sterile hybrid without the poisonous seeds that worry so many people. It develops into a small tree, ideal in small gardens, and the June display of long, bright yellow, pendulous flower clusters is both colourful and stylish. After flowering, it’s unremarkable, but makes a fine host for a clematis. 6m (20ft). H6.

Helenium ‘Moerheim Beauty’

This is a case where an old variety is still a good one. ‘Moerheim Beauty’ has been around for almost 100 years, but its fiery summer flowers, with their appealingly swept back petals, open red then mature to yellow and are an even richer red on the backs. Best in sun, divide and replant every two or three years. 1m (3ft). H7.

Galanthus ‘Straffan’

Many snowdrops thrive on clay soil, especially if split and replanted when the clumps become crowded. ‘Straffan’ is unusual in that every bulb produces two flower stems each season, one taller than the other and one after the other, so the display is extended significantly. The inner petals feature a very distinctive 'Chinese bridge' green mark at the tip. 12cm (5in). H5.

Darmera peltata

This is an easy perennial that enjoys clay soil and damp conditions and which features three different seasons of colour. In spring, before the leaves emerge, clusters of these dark pink-centred flowers open paler pink and fade almost to white on bare stems. The bold green umbrella-like leaves then emerge, and in the autumn the foliage turns bright cranberry red before dying away. 90cm (3ft). H6.

Anemone × hybrida ‘Honorine Jobert’

I hesitate to include this lovely plant because on clay soil it can succeed too well and spread too much. But its bold, weed-smothering foliage followed by its long season of pristine white, gold-centred summer and autumn flowers makes it an essential in a sunny or partially shaded place on clay. Just be sure not to partner it with plants that will be overwhelmed. 1.2m (4ft). H7.

Alnus glutinosa ‘Imperialis’

Alder, Alnus glutinosa, is another British native that’s naturally happy on clay but for our gardens we can choose a variety that’s more attractive than the ordinary wild native type. ‘Imperialis’ has finely cut, jagged foliage that gives the plant an elegant airy look, and the whole tree has a grace we don’t expect from an alder. Happy by water as well as on clay. 6m (20ft). H6.

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