Penstemons in the late summer garden

The late summer charm of penstemons

Credit: Alice Hindley

Penstemon, or beardtongue, is a perfect pick for your late summer garden.

After the euphoria of high summer has faded, there is often an awkward pause in the garden. Many plants, their flowering completed for the year, retreat into the background and even the repeat bloomers take time out to gather their resources for a second performance. This is when the penstemon family shines, keeping the garden colourful through the challenging months of August and September.

Penstemons get their name from two Greek words meaning “five stamens.” Their common name, beardtongue, refers to their hairy lower lip. The tubular flowers end in five flared lobes that are often a contrasting colour to the throat. Being natives of Central and North America, with a range as far north as Alaska, most penstemons are well adapted to our B.C. growing conditions. Plant-hunters began collecting them in the 19th century and British nurserymen were quick to recognize their potential for hybridizing. Today, over 250 species have been identified and the RHS Plant Finder lists around 170 hybrids, with more introduced every year.

Perfect for the late summer garden

Although they begin to flower in June, penstemons will go on making a good show until late in September, especially if spent flower stems are promptly removed. With grass-green foliage sometimes tinged with bronze, and a wide range of colours, they grow on average to a practical 75 centimetres, demanding little more than well-drained soil and a sunny location.

They are generally listed as hardy in zones 7 to 10, but will survive in colder climates as long as the soil is not too wet. At all costs the crown should be kept dry, which means that any protective covering should be of a dry material like leaf litter or dry peat. A cloche of some kind works better than a mulch. Even in milder areas, the secret to penstemon success is to resist any urge to cut them back before spring is truly under way and new growth is visible at the base.

The many faces of penstemon

The most popular penstemon, and one of the hardiest, is raspberry-pink ‘Andenken an Friedrich Hahn,’ whose mouthful of a name is often replaced in North America by ‘Garnet.’ It is a perfect match in my garden for the watered silk colours of an old rose, ‘Alain Blanchard.’ ‘Rich Ruby’ has a larger flower and a deeper velvet colour, but it hasn’t the same tolerance for frost. Similarly, among the paler pinks, pretty ‘Hidcote Pink’ is surpassed in vigour by ‘Evelyn,’ which is a soft strawberry shade.

Between ‘Thorn’ and ‘Apple Blossom,’ both of which are lipstick pink with white throats, I find ‘Thorn’ to be the stronger survivor and the one more inclined to develop into a good-sized clump. ‘Beech Park’ is another good performer in this colour combination and it produces larger flowers.

‘White Bedder’ is a superlative pure white, particularly attractive for the sharp contrast of its anthers against its petals, like grains of black pepper on starched linen. It is also one of the most adaptable and vigorous varieties. A truly Canadian effect might be achieved by planting it with ‘Firebird,’ which is as scarlet as a Mountie’s coat.

Perhaps my favourites are the mauve and purple varieties that look dramatic on their own or blend well with summer pastels. ‘Midnight’ is as dark as its name suggests, while ‘Sour Grapes’ and ‘Stapleford Gem’ are a mix of pink and pale-blueberry shades with decorative plum striping inside the bell. These two cultivars are often confused, but ‘Sour Grapes,’ the rarer variety, has a distinct lime-green line along the top of its flower tube and it is pinched in slightly behind the five lobes of the flower as if held by an invisible elastic. ‘Alice Hindley’ is vibrant lilac on the outside and a more gentle lavender within that fades to white in the throat. Of all the penstemons in this colour group, ‘Mother of Pearl,’ whose flowers are muted shades of palest blue, lilac and grey, is outstanding for its bushy growth, hardiness and constant bloom.

Unique among the penstemons is one variety appreciated more for its foliage than its flower. Following its introduction, Penstemon digitalis ‘Husker Red’ became such a sensation that in 1996 it was given the prestigious Plant of the Year award by the Perennial Plant Association in the U.S. ‘Husker Red’ develops a rounded rosette of leaves in a dark beet colour, out of which rise long, equally dark flower stems. The blooms themselves are small and a disappointing shade of washed-out pink. Nevertheless, when several plants are grouped together, these pale flowers have an airy presence that can be attractive in front of more strongly coloured neighbours. Fortunately, it is inclined to self-seed and the young plants seem to breed true to their parent.

The following plants are hardy up to the zone number indicated: Penstemon ‘Alice Hindley’- zone 7 • P. ‘Andenken an Friedrich Hahn’ – zone 7 • P. ‘Apple Blossom’ – zone 4 • P. ‘Beech Park’ – zone 7 • P. digitalis `Husker Red’ – zone 2 • P. ‘Evelyn’ – zone 7 • P. fruticosus – zone 3 • P. ‘Hidcote Pink’ – zone 7 • P. hirsutus var. pygmaeus – zone 8 • P. ‘Mother of Pearl’ – zone 7 • P. ‘Sour Grapes’ – zone 7 • P. ‘Stapleford Gem’ – zone 6 • P. ‘Thorn’ – zone 7 • P. ‘White Bedder’ – zone 6 • Rosa ‘Alain Blanchard’ – zone 5

Christine Allen is a member of the Master Gardeners Association, and teaches courses in the VanDusen Botanical Garden Education program. Her latest book Growing Up: A Gardener’s Guide to Climbing Plants for the Pacific Northwest has just been published by Steller Press.