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Setaria viridis

green bristle grass

Overview

Setaria viridis is an annual grass native to Europe and Asia and now naturalized across much of the world as a weed of crops, gardens, and waste ground. It grows 4-40 inches (10-100 cm) tall on slender, often branching stems that root at the lower joints and bend upward, forming loose tufts. The flat leaf blades are 2-10 inches (5-25 cm) long and up to 0.5 inch (1.3 cm) wide, with rough margins and a fringed membrane at the leaf base. From summer into autumn the stems carry dense, cylindrical seed heads 1-4 inches (2.5-10 cm) long, green to purplish, with each tiny spikelet backed by several bristles that give the head a soft, foxtail-like form. The bristles point forward and do not detach with the seed, separating it from the yellow and bristly foxtails. A single plant can shed thousands of seeds that persist for years in the soil, making it a lasting agricultural weed. It grows in full sun on most soils, favoring warm, disturbed, fertile ground, and completes its cycle quickly in a single season. The seed feeds birds and small mammals, and the foliage is grazed while young.

Native Range

Native to Europe and temperate Asia and naturalized throughout North America, South America, Africa, and Australia. It grows in cultivated fields, gardens, roadsides, vacant lots, and other open, disturbed ground.

Suggested Uses

It is seldom planted and is mainly encountered as a weed, though the seed is harvested for birdseed and the young growth grazed as forage. In restoration and disturbed sites it gives short-term cover and bird food before perennial cover takes over.

How to Identify

Recognized by soft, cylindrical green to purple seed heads with forward-pointing bristles that stay on the head as seed drops. The stems branch and bend upward from rooting lower joints, and the leaf bases carry a fringe of soft hairs. The persistent bristles separate it from yellow foxtail and the bristly foxtails.

Appearance

Size & Dimensions

Height4" - 3'4"

Width/Spread6" - 1'6"

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~18 weeks

Summer Fall

Flowering and seed heads form from June through October, continuing until frost. The dense bristly spikes shift from green to purplish as the wind-pollinated florets mature. Seed ripens quickly and drops over a long period, building a lasting seed bank.

Detailed Descriptions

Flower Description

Green to purple

Foliage Description

Green

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 Range5.5 - 7.5(Neutral)

357912

Soil Types

loam sand clay silt

Drainageaverage

Water & Climate

Water Needs

Low

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

This grass grows in full sun on almost any soil and favors warm, fertile, disturbed ground with adequate moisture. It is rarely grown on purpose and is managed as a weed in most settings. Seedlings emerge through the warm season and mature within weeks, so shallow cultivation or mulching while plants are small keeps them in check. Removing the seed heads before they ripen limits the seed bank that drives reinfestation. It tolerates drought once rooted but stays smaller on dry, poor soil. No care is needed where it grows as a volunteer.

Pruning

No pruning is practiced. Where control is the goal, cutting or pulling plants before the seed heads ripen prevents reseeding. Mowed plants can still flower on short stems, so repeated cutting through the season is needed.