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Sonchus, Genus, arvensis, Species,

Genus & species

perennial sow thistle

Asteraceae Europe and western Asia

Attracts Pollinators Attracts Butterflies

SunFull Sun – Part Shade

WaterMedium

HardinessZones 3–9

Overview

Sonchus arvensis is a rhizomatous perennial in the family Asteraceae reaching 24-60 inches (60-150 cm) tall and 24-48 inches (60-120 cm) wide, forming dense spreading colonies via creeping horizontal rhizomes. Stems are erect, hollow, branching in the upper half, carrying milky latex throughout that exudes when cut or broken. Leaves are deeply pinnately lobed with soft spiny-toothed margins, 4-12 inches (10-30 cm) long, clasping the stem at the base with rounded auricles (ear-shaped projections). Upper leaves are smaller and less deeply lobed. Flower heads are bright yellow, 1-2 inches (2.5-5 cm) in diameter and larger than the heads of the annual Sonchus species, composed entirely of ligulate (ray-type) florets with no disc florets. Involucral bracts and peduncles are covered in yellow glandular hairs. Fruit is a ribbed achene with a white pappus. A single plant produces 5,000-20,000 seeds, dispersed by wind. The rhizome system is extensive and brittle and regenerates from fragments as short as 0.4 inch (1 cm). The species is listed as a Class C noxious weed in Washington State and is the most aggressive of the three widespread Sonchus species in the region due to the rhizomatous perennial habit. The species ranks with the most difficult perennial weeds to manage in Pacific Northwest field crops.

Native Range

Sonchus arvensis is native to Europe and western Asia, in cultivated fields, ditches, roadsides, and moist disturbed ground from sea level to approximately 7,000 feet (2,100 m). Naturalized across northern North America. The species ranks with the main perennial-weed problems in Pacific Northwest field crops.

Suggested Uses

Used in Asteraceae identification for the three-species Sonchus comparison: perennial rhizomatous S. arvensis (large heads, glandular peduncles) versus annual S. oleraceus (pointed auricles, soft spines) versus annual S. asper (rounded clasping auricles, stiff spines, curled leaves). The rounded-versus-pointed auricle comparison between Sonchus and Lactuca is a standard identification exercise. The milky latex and all-ligulate heads place Sonchus in the chicory tribe (Cichorieae). Studied in rhizome biology and fragment regeneration alongside Elymus repens (quackgrass).

How to Identify

Separated from Sonchus oleraceus (annual sow thistle) and S. asper (spiny sow thistle) by the perennial rhizomatous habit versus the annual taproot of both annuals, by the larger flower heads 1-2 inches (2.5-5 cm) versus 0.4-0.8 inch (10-20 mm), and by the yellow glandular hairs on the peduncles and involucre versus the smooth or sparsely hairy peduncles of the annuals. All three Sonchus species share the milky latex, the clasping leaf bases, and the all-ligulate yellow heads. Rounded clasping auricles separate Sonchus from Lactuca, which has pointed (sagittate) auricles.

Appearance

Size & Dimensions

Height2' - 5'

Width/Spread2' - 4'

Colors

Flower Colors

yellow

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~6 weeks

Flowers: July–October

Summer Fall

Bright yellow ligulate flower heads 1-2 inches (2.5-5 cm) in diameter, borne July through October over 4-6 weeks. Pollinated by bees, flies, and butterflies. Seeds mature 2-3 weeks after flowering and disperse by wind. In the Pacific Northwest peak bloom falls in August through September.

Detailed Descriptions

Flower Description

Bright yellow; all-ligulate heads 1-2 inches (2.5-5 cm); peduncles and involucres carrying yellow glandular hairs; July-October

Foliage Description

Dark green; deeply pinnately lobed with spiny-toothed margins; clasping the stem with rounded auricles; milky latex throughout; deciduous

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 4-10 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 - 8.0 (Acidic to alkaline)

3579

Soil Types

loam clay silt sand

Drainagemoist

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Care & Maintenance

Care Guide

Listed as a Class C noxious weed in Washington State. Management is slow because of the extensive brittle rhizome system: cultivation fragments the rhizomes, and each fragment as short as 0.4 inch (1 cm) regenerates. Repeated cultivation every 2-3 weeks during the growing season over 2-3 years gradually depletes rhizome reserves. Mowing before flowering prevents seed set but does not eliminate the rhizome network. The species is most competitive in moist fertile cultivated soils. In garden settings, digging to 8-12 inches (20-30 cm) extracts the maximum rhizome length and reduces regrowth. Revegetation with competitive perennial species after management reduces re-establishment.

Pruning

Pruning does not apply in a weed-management context. Stems are cut or mowed before flowering to prevent seed set. Rhizomes are dug to the maximum practical depth, and soil around the removal site is monitored for regrowth from rhizome fragments over the following 2-3 seasons.