Silybum Species, Milk Thistle, St. 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)
Synonym:Silybum intermedium
Synonym:Silybum leucanthum
Synonym:Silybum mariae



Water Requirements:

Average Water Needs; Water regularly; do not overwater

Sun Exposure:

Full Sun


Grown for foliage


Good Fall Color

Foliage Color:

Unknown - Tell us


4-6 ft. (1.2-1.8 m)


24-36 in. (60-90 cm)


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)

Where to Grow:

Unknown - Tell us


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

Bloom Color:

Medium Purple

Bloom Characteristics:

Unknown - Tell us

Bloom Size:

Unknown - Tell us

Bloom Time:

Mid Summer

Late Summer/Early Fall

Other details:

May be a noxious weed or invasive

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


This plant is said to grow outdoors 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

show all

Gardeners' Notes:


On Mar 10, 2016, palmbob from Acton, CA (Zone 8b) wrote:

No experience growing this plant, but we use it commonly in veterinary medicine (and sure it human medicine, too) for treating all sorts of liver maladies- it is not really a medicine, but a nutraceutical product that has supportive actions for the liver, and can be a useful addition to treating most liver diseases.


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.


On May 7, 2011, sueroderus from Bluffton, SC (Zone 8b) 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.


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.


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 abou... read more


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

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


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!!!! :)


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.


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 f... read more


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.


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... read more