Milk Thistle (silybum marianum)

European settlers carried milk thistle with them to North America. An annual or biennial native to the Mediterranean, the herb bears oblong, spiny, variegated leaves and purple flowers, followed by black seeds. The common name milk thistle comes from the milky sap that exudes from the plant’s leaves, as well as its traditional use of stimulating milk flow in nursing mothers.

The name St. Mary’s thistle derives from a Biblical story. According to legend, Mary, mother of Jesus, was resting beneath a thistle plant while nursing the baby Jesus when a drop of her milk fell on the plant, producing the leaves’ characteristic white markings.

Milk Thistle

Plant profile

Common Names: Milk Thistle, St. Mary’s Thistle

Description: Erect stems, up to 6 feet tall; prickly, alternate, lance-shaped leaves contain a milky sap; solitary purple flowers followed by black seeds with hairy tufts

Hardiness: Annual or biennial; hardy to Zone 1

Family: Asteraceae

Flowering: Summer

Parts Used: Seeds and leaves

Range/Habitat: Native to the Mediterranean region, naturalized throughout North America; found in dry soil, roadsides, ditches, and fields

Culinary use

Remove the prickly outside edges of young thistle leaves, then lightly steam the leaves and eat them as a spring vegetable. The seeds are high in antioxidants, protein, and healthy fat. To prepare the fresh seeds, soak them overnight, and then drain them. Use a mortar and pestle or spice mill to grind them into a powder, and sprinkle it on cereal or add it to smoothies. You can also lightly roast the seeds, grind them, and then brew them with water (like coffee) to make a hot beverage. Store whole seeds in your freezer for future use.

Medicinal use

For more than 2,000 years, people have used milk thistle to treat liver conditions such as hepatitis, cirrhosis, and drug-induced damage. The seeds contain silymarin, a complex of flavonoid compounds that are powerful antioxidants that reduce inflammation. Herbalists value standardized milk thistle products for their ability to protect the liver from damage by environmental toxins, medications, and alcohol. More recent studies suggest that the extract may also protect the kidneys in a similar way.

Herbal practitioners also believe that milk thistle can help the liver repair damaged cells and generate new ones. In Europe, milk thistle extract is used along with standard medical interventions to treat poisoning from mushrooms in the genus Amanita, a deadly group of fungi.

Milk thistle has been used to treat poor digestion, female hormone imbalance, constipation, mood disorders, hemorrhoids, varicose veins, atherosclerosis, and skin conditions including psoriasis and acne. Milk thistle seeds are high in protein and linoleic acid, a healthy fat that might help balance the menstrual cycle and improve cardiovascular health.

How to grow it

Considered an invasive (and in some states “noxious”) weed, milk thistle self-seeds readily and is not recommended for the garden. To harvest wild milk thistle, look for the plants in dry, stony soil in fields or ditches. (Be sure the plants have not been treated with an herbicide.) Cut off the seed head after it has dried, remove the seeds, and then remove the hairlike fringe from the seeds.