How to grow penstemons

Choosing penstemon

If you have well-drained soil and sunny places to plant them, penstemons are the perfect plants for your garden.

When choosing the right penstemons for you, bear the following things in mind:

• How hardy do you need your penstemon to be? Choose according to your local conditions. Some penstemons are hardier than others. As a general guide, the thinner the leaves the hardier the penstemon. We've also made it easier by offering these lists of penstemon by hardiness.
• What flower colour do you want? Flower range from whites, through pale pinks, dark pinks, purples and reds. There are plenty of two-tone cultivars as well
• Would you like your penstemon to contrast or complement the other flower colours in the border? Go for those that suit the neighbouring plants or try our Find a Plant tool to select plants to go with your penstemons

Choose penstemon by hardiness

RHS Grower Guide – Penstemon

Buying penstemons

Buy plants in 9cm (3½in) pots or 2-litre containers; both will establish and flower in the first summer. The choice is great and they are widely available in garden centres, nurseries and online.

When to plant penstemons

March to mid May is an ideal time to plant; the soil will be warming up in spring, the roots will quickly settle in, and the plants start putting on growth. If you miss this time, don’t worry, you can plant container-grown plants anytime from March to October, as long as the soil is not too dry or you water to keep it moist.

Where to plant penstemons

In garden borders:

Choose a sunny position with more than half a day of full sun in spring and summer

• Allow 45cm (18in) between plants.
• Plant in a sheltered position with well-drained soil, out of cold winds. Some penstemons tolerate temperatures down to -10°C (15°F) in good positions like this.

In containers

You can also grow penstemons in containers.

How to plant Penstemons

Penstemons are easy to plant - see our guide to planting perennials

Perennials are plants that live for multiple years. They come in all shapes and sizes and fill our gardens with colourful flowers and ornamental foliage. Many are hardy and can survive outdoors all year round, while less hardy types need protection over winter. The term herbaceous perennial is used to describe long-lived plants without a permanent woody structure (they die back to ground level each autumn), distinguishing them from trees, shrubs and sub-shrubs. .

Planting perennials: a step by step guide

Growing specialist penstemons

There is a small group of alpine penstemons that you may find in specialist nurseries. These are usually sold in 9cm (3½in) pots and require a sheltered, sunny position and very well-drained soil. Grow these in gravel gardens, rock or crevice or scree gardens. This group particularly dislikes winter wet, so you may need to erect a perspex cover over your plants; or grow them in a cold frame

Cold frames are glaze box-like structures made from brick or wood with a  hinged or removable, glazed, sloping lid. Useful to protect plants from cold weather over winter or acclimatise (harden off) young plants in spring and provide extra warmth for tender crops in summer. or unheated greenhouse. In containers, use a gritty compost

Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. mix: peat-free John Innes No. 2 with 30 per cent horticultural grit by volume added.

Watering

Water well until plants are established. Aim to water well and occasionally, rather than a little and often. You shouldn’t need to water well- established plants

Established plants have been in their current location for two or three years and so have well-developed root systems able to support strong growth with healthy foliage and flowers. in medium to heavy soils, but plants growing in light, free-draining soils might need watering every two weeks in prolonged dry spells. The aim would be to keep the soil just moist.

If you have planted penstemons into containers, water until it comes through the drainage hole, then leave until the soil is dry at a depth of about 2.5cm (1in) before watering again. A saucer placed under the pot will reduce the amount of watering needed.

Feeding

Mulching plants in borders with well-rotted manure or garden compost

Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. each spring should be sufficient. Penstemon are not very hungry plants in the open garden, but in containers would appreciate an application of a general purpose balanced fertiliser such as Growmore in spring.

Deadheading

Remove spent flower spikes as blooms fade to help encourage a long season.

Overwintering

Hardy penstemons in the open ground should not need any protection. You may want to take cuttings of the more tender cultivars to overwinter in the protection of a greenhouse or coldframe.

In containers

If more than a day or two of freezing temperatures are forecast, wrap containers with a couple of layers of bubble plastic to protect the roots.

Caring for older plants

After about five years, penstemons often need replacing as they become woody and flower less well. Propagating from cuttings means you always have younger ones coming on.

Penstemons can become woody and leggy if they are not pruned hard annually. It’s quite straightforward to do:

• In autumn, cut back plants by about a third, leaving enough foliage to provide winter protection. This helps limit windrock
  This can occur when tall or top-heavy plants, especially those with shallow roots, are buffeted by the wind, loosening their roots. It can impair growth and even lead to the plant being blown over. Solutions include tying the stem to a sturdy support, mounding soil up around the stem base, firming the plant back in, and providing more shelter. and looks tidy
• In April or May, check plants for new shoots at the base or along the stems. Cut down to just above these lowest shoots

Take semi-ripe cuttings 5-10cm (2-4in) long in trays and pots of peat-free cutting compost

Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. in summer or early autumn. This is the easiest way to propagate penstemons.

If you take cuttings

A method of growing new plants from parts of an existing plant, such as sections of root, stem, leaf or bud. When prepared correctly and planted in the right conditions, they can produce roots and eventually become independent plants. There is a wide range of different methods for taking cuttings, depending on the plant and time of year. in early summer, they could be flowering by the end of the season.

Sowing seedis also worthwhile – the seedlings

A seedling is a young plant grown from seed. are often similar but not identical to the parent plant. Sow in spring in a propagator

A propagator is a portable, lightweight structure usually plastic, with a vented or unvented lid to provide a humid, slightly warmer atmosphere. It is useful to help seeds germinate and root cuttings. It may have adjustable, thermostatic temperature control. with the thermostat set to 15°C (60°F).

Generally penstemons are trouble-free, but powdery mildew and frost damage are sometimes problematic.