Photo by Melody

PlantFiles: Milk Thistle, Mary's Thistle
Silybum marianum

Family: Asteraceae (ass-ter-AY-see-ee) (Info)
Genus: Silybum (SIGH-lee-bum) (Info)
Species: marianum (mar-ee-AH-num) (Info)

One vendor has this plant for sale.

26 members have or want this plant for trade.


4-6 ft. (1.2-1.8 m)

24-36 in. (60-90 cm)

USDA Zone 5a: to -28.8 C (-20 F)
USDA Zone 5b: to -26.1 C (-15 F)
USDA Zone 6a: to -23.3 C (-10 F)
USDA Zone 6b: to -20.5 C (-5 F)
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)
USDA Zone 9b: to -3.8 C (25 F)

Sun Exposure:
Full Sun

Plant has spines or sharp edges; use extreme caution when handling

Bloom Color:

Bloom Time:
Mid Summer
Late Summer/Early Fall

Grown for foliage

Other details:
May be a noxious weed or invasive
Average Water Needs; Water regularly; do not overwater

Soil pH requirements:
6.6 to 7.5 (neutral)
7.6 to 7.8 (mildly alkaline)
7.9 to 8.5 (alkaline)

Patent Information:

Propagation Methods:
From seed; direct sow outdoors in fall
From seed; winter sow in vented containers, coldframe or unheated greenhouse
From seed; sow indoors before last frost
From seed; direct sow after last frost

Seed Collecting:
Allow seedheads to dry on plants; remove and collect seeds
Wear gloves to protect hands when handling seeds
Properly cleaned, seed can be successfully stored

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There are a total of 21 photos.
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4 positives
4 neutrals
2 negatives

Gardeners' Notes:

Negative coriaceous On Nov 14, 2014, coriaceous from ROSLINDALE, MA wrote:

Three states have designated this species a noxious weed. In some localities state law requires its eradication.

It has escaped cultivation in 26 states and 7 provinces.

Positive sueroderus On May 7, 2011, sueroderus from Bluffton, SC wrote:

Foliage is wonderful. I have grown this plant for a few years and it is an annual that flowers in the first year in my zone 8b garden. Some years it has grown 4 1/2 feet tall but this year the plants are small, perhaps due to an unusually cold winter. I have one blooming at 1 ft the first week in May. It does reseed but not excessively. Definitely an unusual plant.

Neutral otter47 On May 17, 2010, otter47 from Livermore, CA wrote:

This plant is very common in much of California. Near my house, it grows in large colonies along the arroyo where I walk. It is spectacular in growth and the flowers are attractive, too.

Positive onegoodmelon On Oct 28, 2006, onegoodmelon from Dallas, TX wrote:

My experience with this plant began while taking my dogs on their usual walk. All this spring I watched this little plant, which attracted my attention. It was wild by the side of a road. I saw it when it was just as small as a wee lettuce, and thought it was a slightly different looking dandelion. However, over the summer it grew and grew, and then the beautiful purple blooms took off. It grew to almost 7 and a half feet tall. Had a good west and south exposure. (I am located in Dallas, TX). I started to take some of the blooms and eat the seeds, or make tea out of them, which I believe were very helpful to my liver. I used to be unable to process caffeine or alcohol, but now I am better with those. I am convinced that it is the fresh seeds, at the base of the purple flower about 2 to 3 weeks after they reach full size, that are the most effective. Dried preparations, unfortunately, do not seem to have much effect...

Anyway, the poor plant suffered a slow death from the roots up, but it is covered with seed pods that are now dried up brown. I've opened one of them up, and to my untrained and unknowing eye, the seeds look brown and dead.

Negative cherishlife On Nov 13, 2004, cherishlife from Pocola, OK (Zone 7a) wrote:

Arkansas has this plant listed as a noxious weed in the site.

Neutral PurplePansies On Sep 23, 2004, PurplePansies from Deal, NJ (Zone 7a) wrote:

Very easy from seed.... direct sow after last frost or sow indoors........ However very prone to damping off....... Doesn't love to be transplanted too much when young..... delicate succulent leaves when seedlings...... NOw I just have to wait for it to grow up!!!! :)

Positive nevrest On Sep 20, 2004, nevrest from Broadview, SK (Zone 3a) wrote:

Here in Southeastern Saskatchewan (Zone3), this fairly damp and cool year it grew to about 4 1/2 feet with a leaf spread at the bottom of 2 1/2 - 3 feet with the flower spikes reaching over 6 feet. Spectacular. Especially after the flower heads ( about 30) started.
When early frost threatened, we moved it into the solarium and it did not suffer at all from moving.
Wonderful "teaching" plant....when gramma says do not touch you should not touch!!
Tried the leaves steamed, very tasty but the old leaves are tough.
I will be using the seed pods in dried arrangements.

Positive gershom613 On Sep 19, 2004, gershom613 from Sandstone, MN wrote:

The leaves of this plant are quite spectacular, with irregular white patches that have a silvery sheen in the sunlight. Although some people have described this plant as a biennial, my experience here in Northern Minnesota is that it blooms the first year, but is not hardy over our severe winters, so I grow it as an annual. It is definitely a typical thistle, sharp spines and all, so it is best grown where people will not bump into it, such as at the back of a butterfly border. Butterflies do like the flowers, as well as Hummingbird moths and Sphinx moths. However, the larvae of Painted Lady butterflies, which eat native thistles, do not seem to like the leaves -- at least, I have not seen any on the plants. Still, it is a nice alternative to the more invasive kinds of thistles for butterfly gardeners who want to attract the adult insects. It will self-seed, but is not too invasive because the seeds are heavier than wild thistles, so they drop right around the base of the plant instead of sailing off on the wind. In fact, getting the seeds out of the dried heads takes some digging around inside the seed heads (and heavy gloves -- those spines are SHARP!) I find the best way to collect seeds is to leave the heads on the plant until they turn brown but before they open up the fuzzy part. Clip them off, dry them the rest of the way, then remove the seeds.

Neutral axel On Jul 5, 2004, axel from Hemel Hempstead
United Kingdom wrote:

Spectular foliage when young, but becomes shabby with age. Self seeds. Thorns are long and will pierce thick clothing. Perhaps best grown in pots and only displayed while attractive.

Neutral poppysue On Nov 2, 2001, poppysue from Westbrook, ME (Zone 5a) wrote:

This striking plants common name comes from the legend that Marys milk first made the white markings on the leaves. It is a biennial that will form a huge rosette its first year, and send up tall stems topped with large purple thistle flowers in the second year. If the seeds are started 6 weeks early indoors the plant will flower in the same year. It grows fast and the rippled leaves can become close to 2 feet long when its grown in rich garden soil. The irregular, white markings along the veins make it an attractive garden plant regardless, of its showy flowers. The whole plant is covered with fierce spines so its best to locate it in a place where you wont accidentally brush against it. When in full bloom the flower stalks can be as tall as 5 feet and it will have a spread of 3 or 4 feet. Its very tolerant of poor soils but it wont become as lush and extravagant like it does in a rich soil. The whole plant is edible, the young leaves if you remove the spines, and the flowers are said to be eaten like artichokes.

The plant is becoming known for its medicinal properties. The seeds contain silymarin, which helps restore liver function and improve digestion when there has been damage to the liver. The seeds help protect the liver cells from chemical damage and will regenerate cells, which have already been harmed from drugs, alcohol, radiation, or toxic chemicals. Its often included in formulas for people with hepatitis, cirrhosis, and anyone receiving radiation treatments.


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

Livermore, California
San Diego, California
Gainesville, Florida
Honolulu, Hawaii
Cumberland, Maryland
Boxford, Massachusetts
Halifax, Massachusetts
Coloma, Michigan
Sandstone, Minnesota
Belfield, North Dakota
Haviland, Ohio
Salem, Oregon
Butler, Pennsylvania
New Galilee, Pennsylvania
, Saskatchewan
Okatie, South Carolina
Dallas, Texas

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