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Penstemon strictus (Rocky Mt Penstemon)
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© Stephen Hornbeck, some rights reserved (CC-BY) · iNaturalist

Penstemon strictus

Rocky Mt Penstemon

At a Glance

HabitUpright
Height1-3 feet (30-90 cm)
Width12-18 inches (30-45 cm)
Maturity2 years

Growing Zones

USDA Hardiness Zones

3 - 8
These zones indicate the coldest temperatures this plant can typically survive.
What's my zone? →
Frost Tolerancehardy

Overview

An upright herbaceous perennial reaching 1-3 feet (30-90 cm) tall from a basal mat of leaves with multiple flowering stems. Basal leaves lance-shaped to oblanceolate, 2-4 inches (5-10 cm) long, dark green and glabrous, with smooth margins. Stem leaves narrower and clasping, often with a slight upward curve. Inflorescences narrow erect spike-like racemes 8-20 inches (20-50 cm) long, with flowers held in pairs in a one-sided arrangement at the upper portion of the stem. Each flower 1-1.25 inches (2.5-3 cm) long, deep blue to violet-purple, two-lipped, with the corolla tube widening abruptly and the lower lip flaring outward. Sterile staminode bearded with yellow hairs. Capsules 0.3-0.4 inch (8-10 mm), ripening in late summer. Plants form a dense basal mat that expands slowly over 3-5 years to a width of 12-18 inches (30-45 cm). Foliage often persists through winter as an evergreen basal rosette in zones 4-8.

Native Range

Native to the southern Rocky Mountain region of the western United States, occurring in Colorado, Utah, New Mexico, Arizona, and Wyoming. Found in mountain meadows, ponderosa pine and aspen forest openings, sagebrush flats, and gravelly road cuts at 6,000 to 11,000 feet (1,830-3,350 m) elevation.

Suggested Uses

Commonly planted in mountain native plant gardens, xeric pollinator plantings, and dry meadow restorations at 18-24 inch (45-60 cm) spacing. Suitable for containers of at least 3 gallons (11 L) with adequate drainage. Pairs in cultivation with other Rocky Mountain natives such as Castilleja integra, Hymenoxys hoopesii, and Penstemon eatonii.

How to Identify

Distinguished from related Penstemon species by deep blue to violet-purple flowers held in narrow spike-like racemes (not panicles) with paired flowers in a one-sided arrangement. Basal leaves dark green and glabrous, separating the species from the glaucous foliage of P. pruinosus. Stem leaves often with a slight upward curve, contributing to the species epithet strictus ('upright').

Appearance

Size & Dimensions

Height1' - 3'
Width/Spread1' - 1'6"

Reaches mature size in approximately 2 years

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~5 weeks
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June through August depending on elevation; lower-elevation populations bloom in June, alpine populations into August. Each spike holds open flowers for 3-4 weeks; the full bloom period in a stand extends 4-6 weeks. Plants in cooler summers extend bloom to 6-8 weeks.

Detailed Descriptions

Flower Description

deep blue to violet-purple

Foliage Description

dark green

Growing Conditions

Sun Requirements

Requires 6-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range6.0 - 7.5(Neutral)
357912
Drainagewell drained

Water & Climate

Water Needs

Low

Frost Tolerance

hardy

Time to Maturity

1-2 years to first bloom

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Plant container-grown specimens in autumn or early spring into well-drained loamy or gritty soil. Water weekly during the first growing season; established plants tolerate periods of 3-4 weeks without rain. The species adapts to a wider range of garden conditions than most Penstemon, persisting in moderately heavy clay if drainage is adequate. Powdery mildew develops on stressed plants in humid conditions but does not kill them. Plants establish in year 1-2 and persist 5-10 years; division every 4-5 years rejuvenates older clumps and extends planting life.

Pruning

Cut spent flower stems to the basal rosette after seed has dispersed in late summer. The basal rosette persists as evergreen winter foliage in mild zones; only damaged or dead leaves are removed in early spring. Cut entire plant to 2-3 inches (5-7.5 cm) above the soil in late autumn in colder zones (3-4) where foliage browns over winter.

Pruning Schedule

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summerfall

Maintenance Level

low

Container Growing

✓ Suitable for container growing

Minimum container size: 3 gallons

⚠️ Toxicity Warning

Non-toxic