Different varieties of penstemon are put to the test for long-lasting flowers and hardiness. Here are the results
Walking aound the garden at Sissinghurst today, it's the penstemons that really shine. I saw six varieties in full and abundant flower this morning – 'Evelyn', 'Sour Grapes' and 'Alice Hindley' in the rose garden, 'Ruby' and the similar 'Garnet', with a touch of purple in the pillar box red, on the lower and upper tower lawns, and 'Burgundy' in the famous late summer and autumn purple border.
They remind me why I decided to put in a big trial bed of penstemons this spring at Perch Hill. Until then, I'd only grown 'Raven', 'Garnet' and P. heterophyllus 'Heavenly Blue', but Sissinghurst last September convinced me to launch into penstemons in a more dedicated way.
This spring we carried out a mini trial on 15 varieties to work out which we liked and which performed longest and hardest. Many have excelled, without a break in their flowering, from May or June until now. We've picked and picked and most have not batted an eyelid, so next year, this selection of 10 will make it out of their trial corner into one of the central, sunnier, more prominent beds.
My top 10 penstemons
1 'Pensham Just Jayne' 10/10
A lovely deep pink bred in Pensham, Worcestershire, and one of the Pensham series of penstemons – robust, stronger growing with larger, showy flowers. They seem to stand our unpredictable climate better and will overwinter well.
2 'Raven' 9/10
Delicious, strong, deep purple with no white throat, similar to 'Purple Bedder' (also excellent) but with larger flowers. It's a strong grower and one of my favourites for arranging, lasting well if the stems are seared (see below). This does not always survive winter so propagate in autumn.
3 'Burgundy' 9/10
Very similar to 'Raven' in outer petal colour, but more port-wine red than purple. White throat. An excellent doer, but does not always overwinter so propagate every year.
4 'Garnet' (syn. 'Andenken an Friedrich Hahn') 9/10
The hardiest of the varieties we've trialled, with narrow, deep red flowers, which I remember overwintered in my parents' garden when I was young. It has elegant, narrow, willow-like leaves. I find this is best grown with support from a hidden hazel frame. It gets tall and rather chaotic-looking by the end of the year, but you mustn't cut any of this down until March or April. The top growth protects the potentially tender crown.
5 'Penbow' (syn. Jean Grace) 9/10
Electric luminous blue, like 'Heavenly Blue', but never seems to stop growing and flowering. This is a favourite of Derry Watkins (Special Plants). She says she cuts down her show plants and puts them away, only to find them blooming at least 3ft high the following week. May not overwinter and unreliable in propagation, hence not a 10/10.
6 'Snow Storm' (syn 'White Bedder') 8/10
A good white with the odd tinge of pink and an upright, strong grower. Not reliably hardy so propagate every year. For a white, try also P. scouleri 'Alba', another recommendation from Derry Watkins. It flowers from May, and is long blooming, thrives in full sun and good drainage.
7 'Alice Hindley' 8/10
Tall and upright, with flowering spikes growing at least 3ft without support. This has purple, flushed white and mauve flowers with a broad, tubular shape. Flowers from June to October or November and seems to overwinter well.
8 'Evelyn' 8/10
Red-pink, thin tubular flowers, with fine willowy leaves. This is one of Bob Brown's favourites (Cotswold Garden Flowers). He finds the "ranginess" of penstemons difficult – some tend to collapse from the heart with octopus limbs if not supported – but 'Evelyn' has a compact habit and fine foliage. Harriet Hardiman at Hayloft Plants says the trick to prevent penstemons from flopping is to cut back to the lowest shoots in spring, after frost has passed.
9 P. heterophyllus 'Heavenly Blue' 7/10
This flowers longer and harder than most in sun or part shade and benefits from regular picking or deadheading. Even if it's almost over, deadheaded and given a quick boost of seaweed, it bursts into flower again. The downside is it has a lower, more spreading habit than most, so is best poking out from the edge of a skirt of something taller. Should overwinter in a sheltered spot.
10 'Apple Blossom' 7/10
White washed with pink, a compact, vigorous and quick growing variety, so good for picking.
- All these varieties perform well in well-drained soil in full sun. They do fine, but flower less, in partial shade.
- Deadheading the flower spikes is important to encourage repeat flowering from June to November.
- Penstemons have a reputation for being unreliably hardy, which may be partly due to being cut back too early. Resist pruning until frosts have passed, then prune to about 6in, to encourage a bushy habit with growth that will flower well in summer.
- To use as a cut flower
- Strip the leaves from the bottom third of the stem. Sear ends in boiling water for 30 seconds and rest overnight in cold water before arranging. They should last 5-7 days.
The Telegraph | By Sarah Raven