Milk Thistle
Silybum marianum
Milk thistle is a striking, spiny thistle with white-marbled leaves and purple flower heads, long valued as a liver tonic. Its seeds yield silymarin, the basis of its herbal reputation.
- Light
- Full sun
- Water
- Low; drought-tolerant
- Difficulty
- Easy
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Overview
Milk thistle is a tall annual or biennial in the daisy family (Asteraceae), instantly recognizable by its glossy green leaves boldly marbled with white veining and its large, spiny purple flower heads. The white marbling gave rise to the legend that it came from the Virgin Mary's milk, hence the names 'Mary thistle' and 'holy thistle'.
It is best known medicinally for its seeds, which contain silymarin, a flavonoid complex traditionally used to support liver health. Robust and self-seeding, it can become a weed in warm climates.
How to identify it
- Leaves: Large, glossy green with distinctive white marbled veins, deeply lobed and edged with sharp spines
- Flowers: Large, solitary, purple-pink thistle heads surrounded by stout spiny bracts
- Habit: Bold, erect plant typically 1-2 m tall
- Seeds: Shiny brown-black seeds (achenes) topped with a tuft of white hairs (pappus)
- Stems: Thick, grooved, branching
Care & growing
- Light: Full sun
- Water: Low; very drought-tolerant once established
- Soil: Tolerant of poor, dry, well-drained soils
- Temperature: Hardy, roughly zones 5-9; grown as an annual or biennial
- Feeding: Not needed; thrives on lean ground
- Propagation: From seed sown in spring; it self-seeds readily, so deadhead before seeds disperse if you want to prevent spreading
Habitat & origin
Milk thistle is native to the Mediterranean region, southern Europe and the Middle East, growing in dry, sunny, disturbed ground, roadsides and overgrazed pastures. It has naturalized widely in North and South America, Australia and elsewhere.
In many warm regions it is regarded as an invasive weed of rangeland. It is also cultivated, particularly in Europe, for the medicinal seed and silymarin trade.
Uses & benefits
Milk thistle's main use is medicinal: extracts of the seed (standardized to silymarin) are widely sold as supplements traditionally taken to support liver and gallbladder function and protect against toxins.
Historically the plant was also eaten — the young leaves (despined), stalks, roots and flower heads are edible and were used as a vegetable. It is a good pollinator plant, and the seed-tuft fluff attracts goldfinches and other seed-eating birds.
Frequently asked questions
What is milk thistle used for?
Its seed extract, rich in silymarin, is traditionally used to support liver health and is one of the most popular liver-tonic supplements, though you should consult a professional before using it.
Why is it called milk thistle?
Because of the milky-white marbling on its leaves, which legend attributes to the Virgin Mary's milk falling on the plant.
Can you eat milk thistle?
Yes. Once the spines are removed, the young leaves, stalks, roots and flower buds are edible and were historically used as a vegetable.
Is milk thistle invasive?
It can be. It self-seeds prolifically and is a noxious weed in some warm regions, so deadhead it before the seeds disperse if you grow it in a garden.
Milk Thistle guides
In-depth guides for identifying, growing, and caring for Milk Thistle.
