Plants that are at their best in August

August is difficult. The water table is often low, so the garden looks tired and there’s also a natural lull between summer and autumn-flowering perennials. However there are plants that lift the garden. Three (dahlias, salvias and penstemons) are sun-loving, drought-tolerant plants from the Americas and they begin to perform strongly as the days shorten, going on until late.

Silver leaves shine in August, flattering dark-leaved sedums like ‘Purple Emperor’ and ‘Karfunkelstein’. These fleshy-leaved sedums peak in August attracting butterflies and bees. Add a buddleia, a Viticella clematis, some yellow and orange daisies with some touches of blue. Try Agastache ‘Blue Fortune’. Then August will never seem dull again.

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Buddleia x davidii

Buddleias shine in August and they are the best butterfly of all so everyone should plant one.  However the spent flowers must be removed as they brown in order to keep the flowers coming: this will also prevent unwanted seedlings. Cut back hard to the lowest shoots in late-April for August flowers. ‘Lochinch’ is a subtle buddleia suitable for smaller gardens, with silvery foliage and slender lavender flower-spikes. Each flower has an orange eye. Larger buddleias include ‘Pink Delight’, ‘Royal Red’ and ‘Black Knight’. All are popular with butterflies, but the nectar will only flow abundantly in warm, sunny positions.

Heleniums

Heleniums are colourful daisies with velvet middles and petals that come in shades of foxy red, orange and yellow. There is a huge range, flowering at different times, but generally taller heleniums are later. You will need fertile soil, as these struggle otherwise, with one exception - ‘Sahin’s Early Flowerer’. This hybrid helenium tolerates drier conditions, repeat flowers if deadheaded, and each flower is slightly different. It reaches three feet in height and forms a tight clump.

Hardy Geraniums - ‘Patricia’, ‘Rozanne’ or ‘Orion’

These sterile hardy geraniums repeat-flower, but they all take up space.  Patricia (a dark-eyed magenta) and Orion (the best deep-blue) begin flowering in May, forming large mounds.  Cut them back to nothing at the beginning of July: they will reshoot within days and flower within four to five weeks and look fresher for it.

Rozanne is a softer blue and more sprawling in habit. It flowers later and, at RHS Wisley, they give 'Rozanne' the Chelsea Chop to delay flowering until mid-August.

Smaller August-flowering geraniums include the pale-pink ‘Mavis Simpson’ and the magenta ‘Russell Pritchard’, but lots of others will be on offer in garden centres. Avoid G. x oxianum if you resent seedlings.

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Penstemons

Penstemons and will be available from garden centres throughout summer. When planting a mature flowering penstemon, fill the hole with water first and then be prepared to water. Opt for a dark-purple, or a claret penstemon like ‘Andenken an Friedrich Hahn’ (syn. ‘Garnet’) to provide contrast.

Dahlias

Dahlias are easily available from garden centres and are ideal for sunny positions. Look out for Dahlia ‘Knockout’ (syn ‘Mystic Illusion’), an award-winning, chocolate-leaved, single yellow bred in New Zealand. Or you could use the butterscotch-orange double ‘David Howard’. Deadhead after flowering to prolong flowering season.

Agastache ‘Blue Fortune’

This blue bottlebrush, which adds all important vertical accents, should survive through harsh winter in most gardens, although those on heavy clay might struggle. Aromatic foliage and the longest-lived of all for me (3ft/1m).

Aster x frikartii ‘Monch’ and Rudbeckia fulgida var. deamii

I wouldn’t put two daisies together normally but these are superstars, flowering form July to September. Both are long-lived and clump-forming with neat daisies that flatter each other. The rudbeckia bears golden-yellow flowers, middled cleanly in brown, and the aster has long, lilac to lavender lashes. They won’t need deadheading and they are bombproof.

Shrubby, hardy salvias

S. microphylla and S. x jamensis will overwinter in a well-drained sunny position and they flower for midsummer until November. They are not showy, with winged flowers mostly in scarlet, pink and white, but they provide reliable sparkle and insects love them. ‘Dyson’s Crimson’ or ‘Silas Dyson’ are hardy, lipstick-pink salvias that will flower until November.

Viticella clematis

These small-flowered, easily grown clematis, originally bred from a Spanish drought tolerant species, peak in July and August. Pruning is simple. Cut down to the lowest buds every spring. The most highly regarded, picked by the British Clematis Society, is ‘Étoile Violette’. The gappy, purple flowers have a pale-yellow boss of stamens. Let them sprawl gently through a shrub, like Cotinus coggygria ‘Royal Purple’, or they can follow on after a rambling rose like ‘Goldfinch’, or they can be trained onto walls or pergolas. Some are more vigorous than others though. The perfect and easy support is a wire tensioning system called Gripple.

Other Viticella varieties

There are many viticellas in a range of colours and flower shapes, from nodding bell to open flower. Some, like ‘'Étoile Violette' have regular symmetrical flowers and others are misshapen with green-tinted petals, such as the white ‘Luxurians Alba’.

The magnificent seven

‘Betty Corning’
A nodding, frilly grey-blue bell with pink veining. Also scented. Discovered in America by Betty Corning in 1933.

‘Kermesina’
A large, vigorous plant, with deep-crimson flowers, also successful in shade. Lemoine 1883.

‘Mary Rose’
A double, with longer-lasting flowers in navy-blue. Believed to date from the 1500's, but rediscovered in the year the Mary Rose was raised, 1982. 

‘Polish Spirit’
Small flat-faced purple flowers, but useful as it flowers so late, spanning August and September. Raised in Poland by Brother Stefan Franczak and introduced in 1990.

‘Prince Charles’
A soft-blue, to almost silver-lilac, open-flowered clematis with ruched flowers. Bred in New Zealand and introduced by Jim Fisk in 1986.
 
‘Purpurea Plena Elegans’
The damson form of ‘Mary Rose’, with double pom poms, and probably my favourite vitcella of all. Raised by Morel in 1899.

‘Royal Velours’
Almost round, velvety-textured rich-red flowers and quite unique. Raised by Morel in 1900.

Good performers for August at a glance

• Sedum ‘Purple Emperor’ 
• Hardy Geraniums - ‘Patricia’, ‘Rozanne’ or ‘Orion’
• Buddleia x davidii
• Heleniums 
• Agastache  ‘Blue Fortune’ - best foil for golden summer daisies
• Penstemons 
• Dahlias
• Aster x frikartii ‘Monch’ - the longest flowering aster of all with large lavender diasies
• Rudbeckias - yellow daisies
• Salvias - particularly named forms of  S. microphylla and S. x jamensis
• Viticella Clematis

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