Penstemons need good drainage, but Nick Hamilton grows them successfully on his heavy clay soil – and they are hardier than you might think, he says
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| Penstemon 'Catherine de la Mare'
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'There is a popular misconception that penstemons are not reliably winter hardy, and most gardeners treat them as tender perennials – but many varieties originate from the Rocky Mountains area of North America and are as tough as old boots.'
'Do not be fooled into thinking that the hybrid penstemons are the only worthwhile varieties to grow just because they have the largest flowers; many species deserve a space in the garden.'
For more than 20 years the herbaceous borders in the gardens at Barnsdale have relied on penstemon for non-stop colour throughout the summer and autumn. So far, I have amassed more than 170 varieties, although some are so similar they need to be placed side by side to tell them apart.
Penstemon history
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| Penstemon 'Osprey'
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The plants came to prominence in the 19th century when they were brought over from France to be grown as a cut flower, with the French having originally discovered them in North America. Their name comes from the fact that they have five stamens, however, only four of these are fertile, with the largest being sterile.
Old and new varieties
One of the main breeders then was John Forbes, who carried out his breeding at his nursery in the Scottish Borders – he was looking for the biggest and blousiest flowers possible that would look spectacular in vases. Many of the varieties he bred are still in cultivation today. Since then, there have been several breeders that have introduced a number of new varieties. Ron Sidwell's varieties are all named after his passion for birds, such as 'Blackbird', 'Flamingo' and 'Osprey'. Recent new varieties include the Pensham range, the Pershore and Patio Penstemon.
Do not be fooled into thinking that the hybrid penstemons are the only worthwhile varieties to grow just because they have the largest flowers; many species deserve a space in the garden.
Not hardy – not true...
There is a popular misconception that penstemons are not reliably winter hardy, and most gardeners treat them as tender perennials – but many varieties originate from the Rocky Mountains area of North America and are as tough as old boots. Over the past 12 years, we have been working closely with two of the top penstemon experts, Clive and Kathy Gandley, who have been researching this very topic.
The first thing to bear in mind is that a lot of the modern-day cultivars were bred in the Borders, not the warmest part of Britain, and that their natural habitat is at fairly high altitudes where it is not very warm. The important aspect of both these situations is that they were growing in a soil with sharp drainage.
Penstemons need good drainage
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| Penstemon 'Geoff Hamilton'
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The Gandleys came to the conclusion a long time ago that excessively wet soil accounts for the majority of winter casualties. It is therefore very important to avoid losing the plants in a wet winter by improving the drainage of the area the plant will inhabit. I like to improve any area I am planting into with well-rotted garden compost, but with penstemon I throw in a bucket of coarse grit as we have a heavy clay soil that is poorly drained in the winter. The plants are fairly shallow-rooted, so the drainage needs to be improved just enough to take any excessive water away from the roots.
Growing in raised beds
Years ago, I commandeered a raised bed to grow a lot of my collection, because raising the soil in this way improved the drainage dramatically. Most of the varieties have been growing in situ for more than 10 years now.
We are in the process of growing some plants at the top of molehill-like mounds to see if this helps with the survival rate on our very heavy clay soil. The added bonus of the raised bed is that it has a Prunus cerasifolia 'Nigra' planted in the middle, so half of the bed is in semi-shade, with the other half in full sun, which allows us to show visitors that penstemons are happy in either situation.
Some years ago I was concerned that my Penstemon 'Rubicundus' seemed to last for only two to three years before dying. I asked the Gandleys about it while they were carrying out their research trials. They weren't sure at the time, but thought that the larger-flowered varieties should be treated in the same way as the short lived perennial wallflowers – this seems to be holding true with their current trials. The varieties in question tend to be vigorous growers that get woody at the base and produce masses of very large flowers and effectively flower themselves to death. Good for the gardener, but not for the plants! Take a cutting in the second year to ensure a plant of good size to replace the mother plant when necessary.
Deadhead for flowers from June to October
In order to ensure the hybrid varieties have a flowering period from June right through into October, and sometimes as late as December, it is important to regularly deadhead the flower spikes that have gone over. This prevents the plants from setting seed, which is not required, and means that they are able to put more effort into producing more gorgeous flower spikes.
Leave the tops on plants
Once they have finished flowering, the plants can be tidied up by removing all the spent flower spikes down to the nearest set of leaves, but no further. It is important that the tops are left on the plants in order to protect the new young shoots bursting through in the spring. Therefore, all varieties that grow up to 90cm (3ft) are then cut back about the middle or end of April, right down to the mass of young shoots appearing at the base of the plant.
It is important to carry out this task every year as it not only rejuvenates the plant so that it produces stiffer stems that carry the continual display of flower spikes much better, but it also stops the base of the plant becoming woody, thereby prolonging its life. If the plants are not cut back they become over-heavy with blooms so that the stems cannot take the weight and they will then invariably flop over, with the bases of these stems becoming woody very quickly, dramatically shortening the life of the plant.
Tall varieties
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| Penstemon 'Alice Hindley'
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Varieties that flower on stems that grow higher than 90cm (3ft) can have the old flower spikes cut back once they have finished flowering, and in the spring the whole plant can
be tidied up, removing damaged or dead leaves and no more. They may look a little tatty for a few weeks, but if cut back the plants take so long to reach their flowering height, it is not worth doing. Unlike the shorter varieties, the stems of these taller plants are naturally
stronger, so are able to carry the blooms year on year, and surprisingly they do not seem to be affected by the basal woody stem problem. Species and semi-evergreen varieties can be tidied in autumn and cut back, if necessary, in April.
How to take cuttings
You can increase your stock of penstemons by propagating the hybrids by softwood tip cuttings, although we have found greater success removing the growing tips of these cuttings. Being organic, we do not apply any rooting hormone. We find that from May to September we can have our cuttings rooted in about three to four weeks by inserting them into a peat-free compost in an 8cm (3in) pot, covering the cutting with a plastic bag held onto the top rim by an elastic band.
Most species will propagate easily from seed, although some will also multiply happily using the cuttings method.
Nick's choice for borders
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Penstemon digitalis 'Husker Red' – one of my favourites for value-for-money colour. It not only produces 90cm (3ft) spikes of small, white flowers, but also has fantastic beetroot-red evergreen leaves.
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Penstemon strictus – a species that stays low to the ground and has violet-blue flowers that seems to thrive on our poorly drained border soil.
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Penstemon 'Alice Hindley' – one of those taller varieties that does not need to be cut back in April as it reaches 120cm (4ft) with a continual display of large, lilac and white flowers. Identical to this, but with large, rose-pink flowers where the front fades to white, is 'Rosy Blush'.
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Penstemon 'Geoff Hamilton' – my favourite of all. It's an obvious choice, but I wouldn't recommend it if it wasn't a fantastic variety, producing a non-stop display of wine-red flowers that become translucent in the evening light. We've got him dotted all over the gardens at Barnsdale – and he's loving it!
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Penstemon 'Phoenix Red' – a variety specially bred to withstand heat, so it is ideal for a very sunny spot, and the large white throat really sets off the whole flower. This is also the case for
Penstemon 'Maurice Gibbs'. Not named after a Bee Gee, this variety produces a fantastic display of cerise flowers, with the intensity of the flower heightened by the large white throat.
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Penstemon 'Snowstorm' – a pure-white variety. I find that white in the garden, particularly in the semi-shade areas, really lifts the surrounding plants and there are several varieties that will do this.
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Nick Hamilton with his wife Sue
at Barnsdale Gardens
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Penstemon 'Stapleford Gem' – causes confusion because it is usually sold as 'Sour Grapes'. This variety is planted in a spot just outside the Modern Estate Garden at Barnsdale, where the flowers glow when it catches the evening sun.
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Penstemon 'White Bedder' – white with some pink in the bud, which transfers into the flower. For varieties that have slightly more pink, 'Thorn' is very subtle, while 'Flamingo' and 'Osprey' leave less to the imagination.
Look further
Barnsdale Gardens in Rutland, Leicestershire, are the creation of the late Geoff Hamilton who was much loved by the public as a gardener and TV presenter during his lifetime. Today, Barnsdale Gardens continues to thrive and win awards in the hands of Geoff's son Nick, together with Nick's wife Sue. The gardens, shop and nursery are open to the public every day except 22 and 25 December, and sell a selection of Barnsdale-themed and other garden products online.
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