What hardiness zones is Pennisetum setaceum suitable for?

Pennisetum setaceum (syn. Cenchrus setaceus) is a warm-season, clump-forming perennial grass in the Poaceae spp. family, growing 24–48 inches (60–120 cm) tall and 24–36 inches (60–90 cm) wide in a dense, arching, fountain-like mound. Leaf blades are narrow, 0.1–0.15 inch (2–4 mm) wide, bright green, rough-textured, and arch outward from the clump centre. The inflorescence is a cylindrical, bristly, bottlebrush-like spike 6–15 inches (15–38 cm) long, pinkish-purple to tan, produced on arching stems above the foliage from midsummer through autumn. Native to open, rocky habitats in East Africa, the Middle East, and southwestern Asia, the species is listed as invasive in Hawaii, California, Arizona, and many tropical and subtropical regions worldwide; seed is wind-dispersed, and the species colonises disturbed ground, roadsides, and dry slopes, displacing native vegetation. In Hawaii alone the species has occupied more than 500,000 acres and increases fire frequency in dry ecosystems. The cultivar P. setaceum 'Rubrum' (purple fountain grass) carries dark burgundy-purple foliage and deep rose-pink spikes, and is sterile or near-sterile in most climates, lowering invasion risk relative to the green-leaved species type. In the Pacific Northwest, plants are killed below 20°F (-7°C) and are grown as annuals or overwintered indoors.

Native Range

Pennisetum setaceum is native to East Africa (Ethiopia, Eritrea, Kenya, Tanzania), the Arabian Peninsula, and southwestern Asia. It has naturalised widely in tropical and subtropical regions worldwide, including parts of the Mediterranean, southern Africa, Australia, Hawaii, and the southwestern United States.

Suggested Uses

Used as an ornamental grass in borders, containers, and mass plantings for the arching flower spikes and fountain-like habit. The cultivar 'Rubrum' (purple foliage) is widely grown in annual container combinations and municipal seasonal plantings. In the Pacific Northwest, it is grown as a warm-season annual accent in 5-gallon (19 L) or larger containers and in warm border positions. The green-leaved species type is regulated as invasive in Hawaii, California, Arizona, and other tropical and subtropical regions.

How to Identify

Identified by a dense, arching fountain-like grass clump and cylindrical, bristly, pinkish-purple to tan flower spikes 6–15 inches (15–38 cm) long held on arching stems above the foliage. Separated from P. alopecuroides (Chinese fountain grass) by the longer, more arching spikes and the P. setaceum hardiness range that excludes most of temperate North America. The cultivar 'Rubrum' is recognised by the dark burgundy-purple foliage and deep rose-pink spikes.

Appearance

Size & Dimensions

Height2' - 4'

Width/Spread2' - 3'

Reaches mature size in approximately 1 years

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~12 weeks

Summer Fall

Bottlebrush flower spikes emerge from July through October, arching above the foliage on slender stems. Each spike is 6–15 inches (15–38 cm) long and shifts from pinkish-purple to tan as the seed matures. Flowers are wind-pollinated, and the species type produces wind-dispersed seed. The cultivar 'Rubrum' is sterile or near-sterile and rarely sets viable seed.

Detailed Descriptions

Flower Description

Pinkish-purple to tan

Foliage Description

Bright green (species); dark burgundy-purple ('Rubrum')

Growing Conditions

Sun Requirements

Full Sun

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 Range5.5 - 7.5(Neutral)

357912

Soil Types

sand loam rocky

Drainagewell drained

Water & Climate

Water Needs

Low

Frost Tolerance

tender

Time to Maturity

1 year from seed or division

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Site in full sun in any well-drained soil with a pH of 5.5–7.5. Tolerates drought, heat, lean soil, and wind once established. Space plants 24–36 inches (60–90 cm) apart for mass plantings. In USDA zones 9–10 the species is perennial and is regulated as invasive in several states and territories including Hawaii, California, and Arizona. In zones 7–8, plants are root-hardy with winter mulch but top growth dies back. In USDA zone 8 of the Pacific Northwest, the species is grown as a warm-season annual or in containers overwintered above 32°F (0°C). The cultivar 'Rubrum' is sterile or near-sterile and is typically chosen where the green species type is regulated.

Pruning

Where plants overwinter, cut dead foliage back to 4–6 inches (10–15 cm) in late winter before new growth emerges. Where used as an annual, remove the entire clump after frost-killed foliage browns. No further pruning is required during the growing season.

Pruning Schedule

early spring