Penstemon hartwegii (scarlet beard tongue) — Bushy, upright, semi-woody at the base

Overview

Penstemon hartwegii 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. Penstemon hartwegii grows best in full sun, and tolerates most soils and neutral to alkaline pH. Its UK hardiness is rated H3-H5. Suggested uses include borders, rock gardens and containers. It is native to Mexico.

About

Penstemon hartwegii is a semi-evergreen perennial with well-branched, upright stems and a semi-woody base, notable for racemes of bell-shaped flowers in shades of red to purple. The leaves are narrow, glossy and mid to dark green. It flowers from June to September, bringing sustained summer colour. It suits a sunny, sheltered spot with sharp drainage.

Wikipedia contributors, CC BY-SA 4.0 — Penstemon hartwegii

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 hartwegii originates from Mexico and performs as a semi-evergreen, multi-stemmed perennial in temperate gardens. It carries narrow, glossy leaves and produces racemes of bell-shaped flowers in red to purple hues from June to September, making it a summer and early-autumn feature. Plant it in full sun on a south- or west-facing, sheltered site where soil is light, fertile and free-draining — loam or a sandy mix is ideal. It prefers neutral to alkaline conditions; ensure winter drainage because prolonged winter wet is the most frequent cause of loss. Hardiness is rated H3–H5 (borderline to hardy), so give extra protection or grow in a container in the colder or wetter corners of the UK and move it to a frost-sheltered spot for severe winters. Penstemon hartwegii suits mixed borders, gravel and rock gardens, and containers where its upright flower spikes can be appreciated. Plant on a slight slope or in raised beds to improve drainage, or use grit in container composts to keep the crown dry. Positioned against a warm wall or at the front of a sunny border, its red-to-purple bells provide reliable seasonal colour through the summer months.

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 hartwegii 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
Suggested uses: Borders, rock gardens, containers
Native to: Mexico

Care notes

Pruning and caring for Penstemon hartwegii

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 hartwegii?

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 hartwegii?

Penstemon hartwegii prefers full sun. It suits sheltered positions.

What soil does Penstemon hartwegii need?

Penstemon hartwegii 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 hartwegii?

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.

Is Penstemon hartwegii hardy in the UK?

Penstemon hartwegii 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 hartwegii?

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.

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