Penstemon: how to grow, plus 16 of the best varieties

By Abigail Whyte

Published: Friday, 29 April 2022 at 12:00 am

Few herbaceous perennials are as generous as penstemons. Many start flowering in midsummer and, long after other plants are exhausted, will carry the garden on until the first frosts. So long flowering and floriferous are they that they were used as bedding plants by the Victorians, who planted up whole borders with them to fill the garden with summer colour. Margery Fish, a gardener and writer in the middle of the 20th century, admitted to forever ‘preaching the benefits of Penstemon for continual colour’.

Plant breeders in the UK and North America have recently rediscovered the virtues of penstemons and the past decade has seen lots of new introductions. All the modern forms keep the characteristic tubular colourful flowers that give easy access to bees and butterflies.

IN BRIEF

What A genus of about 250 species of semi-evergreen and deciduous perennials grown for their profusion of flamboyant flowers.

Origins Most are native to North America.

Season The main flowering period is early summer to mid-autumn.

Size From 15cm to 1m tall.

Conditions An undemanding and adaptable plant that grows best in well-drained soil in a sunny situation.

Hardiness Very hardy to frost hardy.

Penstemon is the largest family of flowering plants endemic to North America with about 250 species found in habitats ranging from forests to alpine meadows and prairies. Some are small, low-growing plants suitable for rock gardens and alpine houses and some are taller, more floriferous forms which appeal to modern gardeners. Most of the new hybrids are descended from just a handful of species, mainly Penstemon hartwegii, a semi-evergreen species from Mexico.

Despite there being so many garden forms of Penstemon already available, plants breeders are starting to mine the potential that other species may offer in creating new hybrids. The resurgence in popularity of Penstemon looks to be fuelled by new forms and new colours, which will hopefully secure the plant’s place in our garden palette.

How to grow pentsemon

Where to grow pentsemon

Except in very cold or very wet gardens, penstemons should be easy to grow throughout the UK. They are at their happiest basking in a sunny situation in well-drained soil. Give them plenty of room to grow where they are not crowded out by other plants.

How to care for pentsemon

Regularly cutting down old flower spikes during the summer will prolong flowering and help keep the plant vigorous. After a couple of years plants often become woody and straggly, so need pruning to keep them in shape and to produce new growth. They are not susceptible to specific pests or diseases and often appear in lists of plants that deer and rabbits avoid. Treat that advice with scepticism if your garden is visited by either of these animals and try a couple of plants before investing in what might turn out to be deer or rabbit food.

Producing as many flowers as most penstemons do take a lot of energy, so add compost to the soil when planting. Mulching around the plant in the autumn will feed the soil and also help protect the base of the plant from frosts.

Penstemons with narrow leaves tend to be the hardiest. In general, the broader and fatter the leaves, the more tender the plant. As an insurance against cold or wet winter it is advisable to take cuttings of tender penstemons.

How to take penstemon cuttings

Taking cuttings of penstemons is easy, and if you are new to taking cuttings penstemons are good plants to start with. The cuttings don’t require any special equipment other than a cool, light, airy and frost-free place to keep them in over winter.

Take the cuttings between mid-July and mid-September. Fill a 9cm pot with cutting compost or a 50:50 mix of compost and grit. Collect 10-12cm-long tips of a shoots that do not have flowers. Make the cut with sharp secateurs or a sharp knife just below where the leaves join the stem. Remove the leaves from the bottom half of the cuttings. Cut off the top third of the remaining leaves – this looks drastic but will reduce the amount of moisture the cutting loses. Insert the cutting to about two-thirds of its depth. You should get four or five cuttings into a 9cm pot. Water the pot and keep it in a cool place away from direct sunlight. Keep the compost moist but not wet. In a couple of weeks the cutting will have rooted. You can either pot up the young plants immediately or in the following spring. Both cuttings and newly potted young pants should be kept away from frosts.