Penstemons

How to choose a penstemon

Most garden penstemons are bushy plants of 50 to 90 centimetres with narrow green leaves and upright flower stems. Colour is the main choice. The Blackbird Penstemon is one of the darkest, a deep maroon purple on tall, slender stems. The Sour Grapes Penstemon is an old favourite in soft purple tones, and Penstemon Swan Lake is a white for cooling down a hot colour scheme. Penstemon Port Wine sits in the rich wine red range its name suggests.

The Pep Talk varieties, such as Pep Talk Purple Hartweg's Beardtongue, are compact selections suited to pots and the front of a bed. Planting three or five of one colour together gives a stronger effect than single plants dotted about.

Where penstemons grow

Penstemons are at home in cool and mild temperate gardens, including Melbourne, Adelaide, Canberra, Tasmania, Perth and the tablelands and highlands of New South Wales and Queensland. They tolerate frost and dry summer air, and they cope with coastal Sydney in an open, airy spot. They are less reliable in the humid subtropics and tropics, where summer rain and warm nights can rot the crown.

Full sun and sharp drainage are the two essentials. In a border they pair well with salvias and lavender, which like the same conditions, and the tubular flowers are worked by bees, so they earn a place among bee and butterfly plants. For companions and layout ideas, see our guide to perennial plants for a cottage garden.

Planting and spacing

Plant in spring or autumn in a sunny bed. If the soil is heavy, raise the bed or work in compost and coarse grit so that water drains freely, particularly in winter. Space plants 40 to 50 centimetres apart, set the crown level with the soil surface, and water in. Use a light mulch and keep it pulled back from the base of the stems.

Care basics

Water regularly until plants are established, then deeply in dry spells. Penstemons are reasonably dry tolerant, though they flower longer with some summer water. Feed lightly in spring. Too much fertiliser gives soft, leafy growth and fewer flowers.

The key job is trimming. Cut each spent flower stem back to a pair of leaves or a side shoot as soon as it finishes, and the plant will send up a fresh flush. Leave the main cut back until late winter or early spring, then shorten the whole plant to the new shoots near the base. The old top growth protects the crown through frost. Penstemons tend to be short lived, giving three to five good years, so take tip cuttings in late summer to keep favourites going.

Common questions

When do penstemons flower?

From late spring through summer and into autumn, in repeated flushes if spent stems are trimmed.

Are penstemons frost hardy?

Most garden penstemons tolerate moderate frost, especially in well drained soil. Wet, cold soil in winter does more harm than the frost itself.

Do penstemons need full sun?

Yes, for strong stems and plenty of flowers. They accept light afternoon shade in hot inland areas.

Can I grow penstemons in pots?

Yes. Compact varieties do well in a pot with free draining mix and regular trimming.