Photo by Melody

PlantFiles: Smooth Sow Thistle, Milk Thistle, Common Sow Thistle, Annual Sow Thistle, Hare's Colwort
Sonchus oleraceus

Family: Asteraceae (ass-ter-AY-see-ee) (Info)
Genus: Sonchus (SON-chus) (Info)
Species: oleraceus (awl-lur-RAY-see-us) (Info)

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24-36 in. (60-90 cm)

USDA Zone 7a: to -17.7 C (0 F)
USDA Zone 7b: to -14.9 C (5 F)
USDA Zone 8a: to -12.2 C (10 F)
USDA Zone 8b: to -9.4 C (15 F)
USDA Zone 9a: to -6.6 C (20 F)

Sun Exposure:
Sun to Partial Shade


Bloom Color:
Bright Yellow

Bloom Time:
Late Winter/Early Spring
Mid Spring
Late Spring/Early Summer
Mid Summer
Late Summer/Early Fall
Blooms repeatedly


Other details:
May be a noxious weed or invasive
Drought-tolerant; suitable for xeriscaping

Soil pH requirements:
6.1 to 6.5 (mildly acidic)
6.6 to 7.5 (neutral)
7.6 to 7.8 (mildly alkaline)

Patent Information:

Propagation Methods:
From seed; direct sow outdoors in fall

Seed Collecting:
Allow seedheads to dry on plants; remove and collect seeds

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Gardeners' Notes:

Neutral htop On Mar 6, 2008, htop from San Antonio, TX (Zone 8b) wrote:

Smooth sow thistle, milk thistle, swine thistle (Sonchus oleraceus) is an introduced plant from Europe that can be found growing natively in Texas and numerous other states. It can grow in just about any type of soil; however, it prefers nutrient rich soils. Smooth sow thistle has a considerable variation in leaf form and flower color.

This annual/biennial sow thistle forms a winter rosette, grows from a long taproot and is from 8 inches to 5 feet high. The stout stems are hollow, usually 5-angled, hairless and exude latex when broken. The spined leaves are grayish rather than dark glossy green like prickly sow thistle. However, both species can have some plants that fall in the intermediate range in this regard. In the shade, the leaves may have a have purple blotching The upper leaves are not divided and have a broad-based triangular shape; whereas, the lower leaves are divided to the midrib into lobes with the end lobe being the largest. The lobes clasping the stem have arrow-shaped, pointed tips. Sonchus asper are ear- shaped.

Smooth sow thistle flowers usually from June to August. It can flower in April and continue until the first frost. The pale yellow flowerhead is about 1 inch in diameter when fully open and the flowers appear in loose clusters. Dry, stored seed remains viable for around 10 years.

The smooth sow thistle is used in Greece as a winter salad. The leaves also can be boiled like spinach, mixed with other pot-herbs or added to soups.


This plant has been said to grow in the following regions:

Canoga Park, California
Austin, Texas
San Antonio, Texas
Leesburg, Virginia

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