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Sorghum halepense

Johnson grass

Poaceae

Mediterranean, North Africa, and Asia

Drought Tolerant

SunFull Sun

WaterLow · drought-tolerant

HardinessZones 6–11

Overview

Sorghum halepense is a tall, coarse perennial grass native to the Mediterranean region, growing 2-7 feet (0.6-2.1 m) tall from stout, spreading underground rhizomes. The flat leaf blades are 0.4-1 inch (1-2.5 cm) wide and up to 2 feet (60 cm) long, with a prominent whitish midrib. In summer the stems are topped with large, open, purplish to reddish panicles 6-20 inches (15-50 cm) long that bear paired spikelets and shed abundant seed. S. halepense spreads both by seed and by thick rhizomes that can extend several feet, forming dense stands that crowd out crops and native plants. It was introduced for forage and has become a serious agricultural weed, listed as a noxious weed across much of the United States and many other countries. The foliage can build up cyanogenic compounds and nitrates, especially under drought or frost stress, and is toxic to grazing livestock at those times. It tolerates heat, drought, and a wide range of soils. Growth is fast in warm weather, and rhizome fragments left in soil readily sprout new plants. It dies back to the rhizomes after frost.

Native Range

Sorghum halepense is native to the Mediterranean region and parts of Asia and North Africa. It has naturalized across the warmer parts of North America and worldwide, growing in fields, roadsides, ditches, and disturbed ground.

Suggested Uses

S. halepense was introduced as a forage and hay grass but is now treated mainly as a noxious weed of crops and pastures. Its seed is eaten by some birds, and the tall stands give cover in rough ground. It is no longer planted deliberately in most regions because of its invasive spread.

How to Identify

Identify S. halepense by its tall stems, broad flat leaf blades with a prominent white midrib, and large open purplish panicles of paired spikelets in summer. The thick, spreading underground rhizomes set it apart from annual sorghums and most pasture grasses. It forms dense, tall stands in fields and along roadsides. Seeds are reddish-brown and shed freely.

Appearance

Size & Dimensions

Height2' - 7'

Width/Spread2' - 4'

Colors

Flower Colors

purple

Foliage Colors

green

Bloom Information

Bloom Period

~20 weeks

Spring Summer Fall

S. halepense flowers from late spring through summer and into fall in warm regions, generally May to October. The large purplish panicles release pollen to the wind and set abundant seed. Flowering and seed set continue until frost.

Detailed Descriptions

Flower Description

purplish to reddish

Foliage Description

green with white midrib

Growing Conditions

Sun Requirements

SunFull 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 Range5.0 - 8.0(Neutral)

357912

Soil Types

loam sand clay

Drainageaverage

Water & Climate

Water Needs

Low

Frost Tolerance

hardy

Time to Maturity

1-2 years

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

S. halepense grows in full sun and tolerates heat, drought, and most soils, from sand to clay. It needs little water and spreads aggressively by rhizome and seed, making it hard to remove once established. Rhizome fragments left in tilled soil sprout into new plants. Hardy in USDA zones 6-11, it dies back to the rhizomes after frost and regrows in spring. The foliage can become toxic to livestock under drought or frost stress. Repeated mowing, tillage, or herbicide is used to control it.

Pruning

S. halepense is managed by control rather than pruning. Repeated mowing before seed set weakens the stand and limits seeding. Tillage can spread it by cutting rhizomes into sprouting fragments, so cultivation is timed carefully.