Colourful, long-flowering and popular with pollinators, penstemons are easy to look after and fill your beds with flowers from summer to early autumn. Plant them with sun-loving perennials such as geraniums, rudbeckia and echinacea.
Penstemons are short-lived perennial plants that flower from June through to September or October. They come in a variety of colours, from bright whites and blues to rose pinks, deep purples and claret red, and are a wonderfully low-maintenance addition to herbaceous borders and cottage gardens.
Although the tubular flowers look similar to foxglove flowers, the plants belong to different genera. To add to the confusion, there is a species of penstemon called Penstemon digitalis, cultivars of which include the popular Penstemon digitalis 'Husker Red' and Penstemon 'Dark Towers'.
Most penstemons live for between three and five years, but they're easy to propagate from cuttings, so you can grow your own replacement plants as and when you need them. Some penstemons are fully hardy in the UK, while others are borderline hardy. Penstemon 'Windsor Red' and Penstemon 'Andenken an Friedrich Hahn' (also known as Penstemon 'Garnet') are two good options for colder parts of the country.
Where to plant penstemons
Penstemons enjoy a sunny spot, and while they can cope with a bit of shade, you may get fewer flowers. Plant them in fertile, well-drained soil and avoid exposed sites if possible, particularly if you're growing tender varieties. Penstemon can handle dry soils, but it may struggle in prolonged droughts.
Penstemons are a great filler plant for the middle of large borders. Most grow to between 60 and 90 centimeters tall, but there are shorter varieties like Penstemon 'Pep Talk Purple' and Penstemon 'Pep Talk Red' that look good at the front of beds. These compact varieties are also the best option for pots, though you can grow taller plants in containers, as long as the pot is deep enough to accommodate the roots.
When to plant penstemon
Spring is the best time of year to plant penstemons, as this allows them to get established before winter. You can also plant them in summer and early autumn if the ground isn't too dry.
How to plant penstemons
Before you start preparing the soil, water your plant well. Mix organic matter, such as compost or well-rotted manure, into the soil before planting. If your soil is quite heavy (common with clay soils), you may also want to mix in some horticultural grit to help with drainage.
Dig a hole a little wider than the pot your plant came in, remove the plant from its pot and place it in the hole. Backfill the soil so the top of the rootball is level with the surface. Water deeply and add a layer of mulch if planting in summer to help keep the soil moist. If you're planting several penstemons, space plants around 45 centimetres apart.
When planting penstemon in pots, choose a large container with drainage holes. Fill your pot with peat-free compost. Penstemon are hungry plants, so it's worth mixing in some slow-release fertiliser. Plant your penstemon so the rootball is level with the surface of the compost, a couple of centimeters below the top of the pot. Water it well.
Care of penstemon plants
Water new plants deeply and infrequently to encourage them to develop strong roots. You want to keep the soil moist but not waterlogged. Mature plants should only need watering during dry spells in summer.
Add a layer of mulch around plants in beds in early spring. Plants growing in containers will need more regular watering and feeding throughout the spring and summer.
Hardy penstemons grown in the ground shouldn't need any protection over winter, but less hardy varieties, such as Penstemon 'Apple Blossom' and Penstemon 'Hidcote Pink', may need to be covered with fleece or a cloche if temperatures drop much below freezing. Penstemons in pots will need wrapping in bubble wrap or hessian during cold spells or moving to a frost-free greenhouse.
If you're worried your penstemons won't survive the winter, take cuttings in summer and grow the penstemon seedlings on under cover. You can plant them out in spring to replace any plants that don't make it.
How to deadhead penstemon
Deadheading penstemon flowers as they fade will encourage the plant to produce fresh blooms. Cut the flower spike back to a healthy pair of leaves.
If you have multiple penstemons, you can stagger the flowering period by giving some plants the "Chelsea chop" in late May. Cut back these perennials by a third to a half to get a more compact, bushier plant. These plants will flower later, but you'll still get tons of blooms. If you just have one plant, you can cut back half the stems and leave the others intact for a longer blooming season.
Pruning penstemon
Prune penstemon plants in late April or early May, as new shoots are starting to grow. Cutting back penstemon hard at this time of year means that the plant will grow from the base, giving you bushy foliage and strong stems that can support flowers without flopping. Cut stems just above the lowest shoots.
You can also cut back penstemons by about a third in autumn to tidy up plants and protect them from wind rock (when strong winds blow foliage back and forth, causing the roots to lift). Don't cut stems back completely at this time of year, as the old foliage protects the plant during cold winters.
Penstemon propagation
The best way to propagate existing plants is to take semi-ripe cuttings in summer. Cut just above a leaf on a non-flowering shoot. Pinch out the tip of the shoot and trim the cutting to around 15 cm, cutting just below a leaf node. Strip off the lower leaves and cut any larger leaves in half to reduce water loss. Place the cutting in a pot of cutting compost or compost mixed with grit, water the compost and place in a sunny spot.
You can also grow penstemons from seed. As they need to be started early in the year, it's best to use a propagator so you can give the seeds a consistent temperature of 15-20°C. Sow seeds lightly onto compost between February and April, then prick out seedlings into individual pots once they have a couple of sets of leaves. Harden young plants off before planting them out in the garden after the risk of frost has passed.
Common problems
Penstemons are fairly resistant to common garden pests and diseases. They can struggle from too little water (in droughts) or too much (if you overwater them), and powdery mildew may be a problem for drought-stressed plants.
Our favourite penstemon varieties
Penstemon 'Pensham Czar' produces eye-catching purple flowers that are white inside. It grows to between 60 and 90 centimetres and is hardy throughout most of the UK, though it may struggle in very cold winters.
Penstemon 'Windsor Red' is one of the hardiest penstemons, making it a good choice for colder parts of the UK. It has vibrant crimson flowers, which bloom profusely in late summer, and semi-evergreen foliage.
Penstemon 'Harlequin Magenta' has striking magenta pink flowers. The inside of each flower is a paler colour, with slashes of dark pink stripes. This is a half-hardy penstemon that may need winter protection in colder areas.
FAQ
When should you cut back penstemon?
You can cut back taller penstemons by about a third in October to make the plant look neater and reduce the risk of wind rock. Don't fully cut back the foliage, as it helps protect plants over winter. In April or May, you can cut back penstemons to just above the new shoots. This hard pruning encourages strong, bushy growth.
Do penstemons come back every year?
Penstemons are perennials, which means they will grow back year after year. However, they are classed as short-lived perennials, so they won't last forever. Most plants will live for three to five years, but you can take cuttings and grow new plants to replace them. You may need to protect half-hardy varieties in cold winters or grow them in pots, which you can move under cover.
How can I take penstemon cuttings?
You can propagate penstemon plants by taking semi-ripe cuttings from mid summer to early autumn. Take cuttings from non-flowering shoots and trim to just below a leaf node. Remove lower leaves and place your cutting in a pot of cutting compost. You can plant multiple cuttings in one pot. Place the cuttings in a bright spot and move them to individual pots once roots have developed.
