Penstemon gentianoides (gentian beardtongue) — Bushy, upright, semi-woody at the base

Overview

Penstemon gentianoides is a bushy, upright, semi-woody at the base perennial in the genus Penstemon, part of the Plantaginaceae family, with semi-evergreen or evergreen; narrow, glossy, mid to dark green foliage. It typically grows around 1.5 metres tall. Penstemon gentianoides grows best in full sun, and tolerates most soils and neutral to alkaline pH. Its UK hardiness is rated H3-H5. It is native to Mexico and Central America.

About

Penstemon gentianoides is a semi-woody perennial reaching about 1.5 metres with upright, well-branched stems. It carries narrow, glossy mid to dark green leaves that are semi-evergreen in mild winters. Flowering occurs from June to September on erect spikes of blue-violet blooms. It suits sunlit, sheltered positions where soils drain freely.

Wikipedia contributors, CC BY-SA 4.0 — Penstemon gentianoides

About the genus

Penstemon, the beardtongues, is a large genus of roughly 280 species of flowering plants native to North America from northern Canada to Central America. It is the largest genus of flowering plants endemic to North America. As well as being the scientific name, penstemon is also widely used as a common name for all Penstemon species alongside beardtongues.

Wikipedia contributors, "Penstemon", CC BY-SA 4.0 — Penstemon

In the garden

Penstemon gentianoides comes from mountain regions of Mexico and Central America and forms upright, semi-woody perennial clumps that can reach around 1.5 metres. The plant produces dense bundles of narrow, glossy leaves and bears blue-violet flowers from June to September, making it a summer-flowering presence in the border. Plant into a free-draining, light fertile loam or sandy soil with neutral to alkaline reaction in a south- or west-facing, sheltered spot in full sun. Avoid waterlogging: winter wet is responsible for most losses, so elevate the root zone or plant on a gentle slope or raised bed where soils dry more quickly. Hardiness is H3–H5 (borderline to hardy), so give additional shelter in the coldest sites or favour milder areas of the UK. At around 1.5 metres high, Gentian beardtongue suits the middle-to-back of a sunny perennial border, a gravel garden with good drainage or a Mediterranean-style bed. The tall flowering spikes provide season-long vertical structure from June to September and are effective where you need height without a woody shrub.

Growing conditions

Best soil and position for Penstemon

Sunlight: Full sun
Soil type: Light, fertile, free-draining loam or sand
Soil pH: Neutral to alkaline
Soil moisture: Well drained; winter wet causes most losses
Aspect: South or west facing
Exposure: Sheltered
UK hardiness: H3-H5

Plant details

Penstemon gentianoides size, habit and characteristics

Plant type: Perennial
Habit: Bushy, upright, semi-woody at the base
Foliage: Semi-evergreen or evergreen; narrow, glossy, mid to dark green
Height: 1.5 metres
Native to: Mexico, Central America

Care notes

Pruning and caring for Penstemon gentianoides

Cultivation: Drainage and shelter decide whether a penstemon is perennial or annual in your garden. Plant in spring rather than autumn so the roots establish before winter, and leave the top growth standing until spring as crown protection. Regular deadheading is what sustains the extraordinarily long season. Given the modest hardiness of most cultivars, taking cuttings every summer is sensible insurance.
Pruning: Leave stems intact over winter, then cut back to low healthy buds in mid-spring once frosts have passed. Deadhead continuously through summer, cutting spent spikes to a side shoot.
Propagation: Semi-ripe cuttings taken in late summer root quickly and are the standard method - and the usual replacement for winter losses. Species can be raised from seed.
Pest resistance: Slugs take young spring shoots; capsid bug and eelworm occur but are uncommon.
Disease resistance: Powdery mildew and leaf spot appear on crowded plants. Root rot follows winter waterlogging.

Frequently asked questions

How do I grow Penstemon gentianoides?

Drainage and shelter decide whether a penstemon is perennial or annual in your garden. Plant in spring rather than autumn so the roots establish before winter, and leave the top growth standing until spring as crown protection. Regular deadheading is what sustains the extraordinarily long season. Given the modest hardiness of most cultivars, taking cuttings every summer is sensible insurance.

Where is the best place to plant Penstemon gentianoides?

Penstemon gentianoides prefers full sun. It suits sheltered positions.

What soil does Penstemon gentianoides need?

Penstemon gentianoides is adaptable and grows happily in most soil types, including light, fertile and free-draining loam or sand. It prefers neutral to alkaline soil. Aim for soil that stays well drained; winter wet causes most losses.

How do I prune Penstemon gentianoides?

Leave stems intact over winter, then cut back to low healthy buds in mid-spring once frosts have passed. Deadhead continuously through summer, cutting spent spikes to a side shoot.

How big does Penstemon gentianoides grow?

Penstemon gentianoides reaches a height of 1.5 metres.

Is Penstemon gentianoides hardy in the UK?

Penstemon gentianoides has an RHS hardiness rating of H3, meaning it is half-hardy, tolerating -5 to 1°C, and may need winter protection in colder areas.

How do I propagate Penstemon gentianoides?

Semi-ripe cuttings taken in late summer root quickly and are the standard method - and the usual replacement for winter losses. Species can be raised from seed.

More in the Penstemon genus

Browse all Penstemon →