Penstemon is a tall, spired perennial, that will give you plenty of bell-shaped blooms from June right up until the first frosts. These wonderful flowers come in a range of gorgeous colours. They are easy to grow and propagate and most are hardy enough to make it through a cold British winter. They provide plenty of colour in the later part of the season and attract bees with their nectar-filled flowers.
Read on to find the best penstemon varieties along with guidance on how to propagate, grow and take care of these lovely flowering plants.
Most varieties of this plant bloom in late summer through to early autumn. Their flowers are similar in shape to a foxglove, growing in tall spires of trumpet-shaped flowers. There is a huge variety of colours available, and many have different colours inside the flower trumpet. Some varieties have a slender flower while others are more wide-mouthed. The varieties with narrow leaves tend to be hardier than the broad-leaved varieties.
This variety takes its name from the delicate red foliage rather than flower colour. The contrasting white flowers make this a very attractive plant. It is a reliable variety that comes back year after year and flowers prolifically.
‘Pensham Just Jayne’
This is a lovely deep pink variety with nice, large flowers. It copes with a variable climate and overwinters well.
This variety has large deep purple flowers. It makes a good cut flower. These do not always survive over winter, so it is worth taking cuttings.
This has flowers the colour of red wine with a white throat. It may not survive a harsh winter, so it is worth propagating each year.
‘Andenken an Friedrich Hahn’
Also known as Garnet, this is a very hardy, narrow-leaved variety. The flowers are also narrow and deep red in colour.
This electric blue-flowered variety is vigorous and provides a profusion of blooms. It is a little harder to propagate than some varieties and it may not survive a harsh winter unless planted in a very sheltered spot.
This is one of the best white varieties. Its buds are creamy white, opening to white flowers that are very lightly tinged with pink. It’s a strong upright plant that flowers well.
heterophyllus ‘Heavenly Blue’
I have included this variety as it does well in part shade. It has a lower growth habit, forming more of a clump than some varieties. It flowers abundantly with azure blue blossoms overlaid with hints of pink. It also has lovely grey-green foliage. It overwinters well if planted in a sheltered position.
This pretty variety has white flowers flushed with pale pink. It is a compact variety and produces good stems for cuttings.
This is a stunning variety featuring hot red flowers with a contrasting white throat.
‘Strawberries and Cream’
With pinky-white flowers and deep red markings on the throat, this variety is enough to make your mouth water.
This a taller variety than most reaching 1.2 metres (4 feet) in height. It makes a very sophisticated addition to the garden.
Another tall varieties this has lovely pink flowers with deeper pink markings.
These wonderful plants were a favourite of Victorian gardeners for their abundant blooms and gorgeous colours. They are easy to grow, drought resistant and have the added advantage of being slug resistant.
These plants thrive in good light and will be happiest in a sunny border or bed. When grown in pots, position them on a bright patio or balcony. They will cope with partial shade but may not flower as profusely. However, p. heterophyllus ‘Heavenly Blue’ will flower well even in partial shade.
Penstemon are quite drought hardy once established. On medium to heavy soils, you will not need to water except in long periods of dry weather. On light or sandy soils, they may need watering fortnightly.
These plants require well-drained soil as they hate waterlogging. They do well in light sandy soils, often flowering best in these conditions. They also do well in containers and pots. Often it is cold wet soil in winter that causes these plants to die rather than cold temperatures themselves. If you have a heavy clay soil, you should add plenty of coarse grit before planting to improve drainage.
Fertilise once in spring and again in summer. A rose fertiliser suits them perfectly. Do not over fertilise as this can lead to the plant producing foliage at the expense of flowers.
You should plant your penstemon in late spring or early summer so that they have plenty of time to establish before winter. Choose a position in sun and with well-drained soil. It is not usually necessary to enrich the soil before planting as this can lead to a lush green plant but few flowers. If planting in a pot, use a loam-based potting compost. Though these plants are quite tall they have strong sturdy stems and so will not need support.
Regular deadheading will ensure you have flowers right up until the first frosts. Cut the flower stalks right back to the ground after flowering. A good mulch of well-rotted manure or compost will help your plant get through cold winter weather. Container grown plants will need to be watered once the soil dries out.
Penstemon make a lovely cut flower and should last 5-7 days in a vase. The flowers will last longer if the stems are dipped in boiling water for 30 seconds and then left in very cold water overnight.
Penstemon are not generally a long-lived plant and rarely self-seed in the garden. For this reason, you should consider dividing your plants or taking cuttings in order to have new plants to replace the old ones as they die off.
In spring, you should scrape away the top couple of inches of compost and replace it with fresh. Once the roots fill the pot you should repot your plant into a container that is a couple of inches larger than the existing one. Do not be tempted to put a small plant in a very large container. This would cause the plant to put its energy into root growth and foliage at the expense of flowers, plus large pots stay moist for longer and this can encourage root diseases.
Looks good with
These plants are wonderful for the herbaceous border adding lots of height and colour. Most varieties are the right height for the middle of the border, though some alpine varieties will suit being closer to the front. They flower from late summer up until the first frosts.
In a traditional border or cottage garden, they go well with peonies, roses, fuchsias and hardy geraniums. The darker coloured varieties also look wonderful against silver foliage such as nepeta, artemisia and cineraria or among feathery grasses.
Most penstemons should not be cut back in autumn as the old growth protects the tender crown. However, taller varieties should be cut back by a third in September to reduce the risk of wind damage. Leaving some growth intact will help them survive the winter. In spring, when new growth appears, cut back the old growth to just above the new shoots.
Penstemons are not very long-lived plants and can become rather woody and untidy after about four or five year’s growth. They also begin to suffer more through harsh winters. So, it worth propagating regularly to ensure you always have fresh vigorous plants in your garden.
It is easy to propagate these plants from cuttings or by division.
You should take cuttings in July or August.
Choose stems from the current year’s growth that are just beginning to turn woody. Each cutting should be about 3- 4 inches in length. Cut the base of the stem to just below a leaf node. Remove any flower buds and the bottom set of leaves. If there is only one set of leaves reduce these by half if they are large.
Prepare a seed tray with a mixture of half potting compost and half horticultural grit. Make holes with a pencil and insert cuttings so that most of the cutting is in the compost. Water and place in a sheltered spot. The cuttings can be potted up individually once you see roots emerging from the base of the tray.
Overwinter the plants in a cool greenhouse or cold frame and they will be ready to plant out the following April.
If you choose to propagate your plant by dividing it, this should be done in spring to ensure the plant has enough chance to recover before winter. Wait until the harsh winter weather is well and truly over and the soil has begun to warm.
Water the plants well the day before you make your divisions. Dig up the plant, ensuring you get all the roots, and move it to a cool location. You can then gently break the plant apart ensuring each new section has some roots and leaves. Each new plant can now be replanted into its location in the bed or border or planted up into a container. Water the plants well until they are well established.
If you live in an area with a harsh climate you may like to pot up your divisions and place them in a sheltered spot until they have recovered. They can then be hardened off before planting out.
Common Penstemon Problems
Penstemon are usually healthy plants. Ensuring good conditions will help them stay strong and vigorous.
This plant is not susceptible to many pests and is even slug proof. Occasionally they may get attacked by aphids, such as blackfly and greenfly, which suck the sap of the leaves and cause them to become yellow and curled. These pests can be removed with a strong jet of water or by spraying with a soap solution. Encouraging beneficial insects such as ladybirds can keep populations under control.
Penstemon are occasionally susceptible to fungal diseases. In order to prevent these, you should ensure plenty of air circulation around the plant. Cut back any plants that are overcrowded and remove weeds and plant debris. In addition, water you plant at the base rather than on the leaves and water early in the day to allow the moisture to evaporate before nightfall.
Botrytis leaf mould
This is a fungal disease that may appear as brown spots on the leaves. As the disease progresses it can lead to damaged flowers. You should remove all infected buds, blossoms and foliage. You can treat plants with a fungicide, however, badly affected plants should be disposed of.
This is another fungal disease that can affect penstemon. You may see yellow spots on the leaf surfaces and orangey brown spores on the undersides. This disease occurs mostly in humid weather. Improving air circulation around the plant can help. A fungicidal soap applied in spring can reduce the chance of this disease affecting your plants.
Q My penstemon did not come back after winter. What can I do to make sure this doesn’t happen again?
Firstly, you can choose one of the hardier varieties. In general, those with narrow leaves tend to be able to survive worse weather than those with broader leaves.
Secondly, make sure your soil is well-drained. It is often cold wet soil that kills off these plants rather than generally low temperatures, so add plenty of course grit if you have heavy clay soil.
Thirdly, never cut back your penstemon in autumn. Leaving the top growth over winter provides some protection for the tender crown. Fourthly, mulch the crown of your plant with some well-rotted manure or compost to keep it cosy and warm over winter.
Q My penstemon usually provide me with plenty of flowers but this year they have not flowered so much. Are they reaching the end of their life?
Penstemon are not particularly long-lived plants, however, they can be regenerated by dividing existing plants into several new plants. Ideally, this would be done in spring to give the plants a chance to regrow before winter, however, it can be done in autumn if you have a fairly sheltered garden.
Alternatively, you can divide them in autumn but pot them up and keep them in a sheltered spot or cool greenhouse ready for hardening off and planting up in spring once any danger of frost has passed and the soil has begun to warm.
Rachel Brown is a senior writer at DIY Garden reporting on all things from gardening to fun with the kids. Her expertise stems from a passion to teach her children about the benefits of outdoor play and how to protect the environment.