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Bromus diandrus

great brome

Overview

Bromus diandrus is a winter annual grass growing 12-36 inches (30-90 cm) tall on erect, sparsely branched culms. The leaf blades and sheaths are softly hairy and green, drying to pale straw. Each stem ends in an open, nodding panicle 4-8 inches (10-20 cm) long bearing large spikelets, every floret tipped with a straight rough awn 1.2-2.4 inches (3-6 cm) long. At maturity the sharp-pointed florets break apart with a hardened, needle-like callus that can drive into the mouths, eyes, and hides of grazing animals, the trait behind the common name ripgut brome. Germination follows autumn and winter rains, flowering runs through spring, and the plant dies by early summer. In western North America and Australia B. diandrus forms dense stands on roadsides, fallow fields, and overgrazed range, where the cured biomass adds to summer fire load. It resembles the smaller B. rubens, which has shorter awns and a compact reddish head, and B. sterilis, which has narrower spikelets. One limitation is that its tall litter shades and suppresses low-growing native annuals. Stand density swings widely with winter rainfall.

Native Range

Bromus diandrus is native to southern and western Europe, North Africa, and southwest Asia around the Mediterranean Basin. It has naturalized across western North America, temperate Australia, New Zealand, and South America, and is a widespread weed of grain crops and rangeland in those regions.

Suggested Uses

Bromus diandrus is not cultivated and has no ornamental or forage value once the awns harden. It occurs as a weed of cereal crops, fallow land, and rangeland and is studied for its effect on crop yield and fire fuel. Young plants are sometimes grazed before flowering.

How to Identify

Identify it by the tall stems and open, drooping panicle whose spikelets each carry a rough straight awn 1.2-2.4 inches (3-6 cm) long, far longer than those of B. rubens. The mature florets separate with a sharp, hardened callus. The large nodding spikelets and very long awns distinguish it from other annual bromes.

Appearance

Size & Dimensions

Height1' - 3'

Width/Spread4" - 8"

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~10 weeks

Spring

Flowering runs from April to June in its naturalized range, after autumn and winter germination. The wind-pollinated florets are green, drying to straw as the awns stiffen. Seed shatters in early summer and the plant dies back.

Detailed Descriptions

Flower Description

green drying to straw

Foliage Description

green drying to straw

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 Range6.0 - 8.0(Neutral)

357912

Soil Types

sand loam clay

Drainagewell drained

Water & Climate

Water Needs

Low

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Bromus diandrus grows in full sun on disturbed, fertile, or sandy soils across a soil pH of about 6.0 to 8.0. It is a drought-adapted winter annual that germinates with autumn and winter moisture and matures before summer drought. The species self-sows from a short-lived but abundant seed bank and needs no cultivation. It establishes densely on roadsides, crop margins, and degraded pasture. Stands vary year to year with winter rainfall. It is listed as a noxious or invasive weed in several western U.S. states and Australian regions.

Pruning

As an annual grass, B. diandrus is not pruned. On farmland and range it is mown or grazed before seed set to reduce the seed bank, though the long awns make mature plants unpalatable. Cutting after the awns harden disperses the injurious florets.