Silybum Species, Milk Thistle, St. Mary's Thistle

Silybummarianum

Family
Asteraceae (ass-ter-AY-see-ee)
Genus
Silybum (SIGH-lee-bum)
Species
marianum (mar-ee-AH-num)
Synonym
Silybum intermedium
Silybum leucanthum
Silybum mariae
Sun Exposure
Full Sun
Foliage
Grown for foliage
Deciduous
Good Fall Color
Height
4-6 ft. (1.2-1.8 m)
Spacing
24-36 in. (60-90 cm)
Hardiness
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)
Danger
Plant has spines or sharp edges; use extreme caution when handling
Bloom Color
Medium Purple
Bloom Time
Mid Summer
Late Summer/Early Fall
Other Details
Category
Biennials
Water Requirements
Average Water Needs; Water regularly; do not overwater
Foliage Color
Where to Grow
Bloom Characteristics
Bloom Size
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
Non-patented
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
Regional

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

Butler, Pennsylvania

New Galilee, Pennsylvania

, Saskatchewan

Okatie, South Carolina

Dallas, Texas

show all

Featured Videos

Gardener's Notes:

5
positives
4
neutrals
2
negatives
Sort By:
Sort By:
P
Acton, CA (Zone 8b) | March 2016 | positive

No experience growing this plant, but we use it commonly in veterinary medicine (and sure it human medicine, too) for treating all sorts ...Read More

C
ROSLINDALE, MA | November 2014 | negative

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

...Read More

S
Bluffton, SC (Zone 8b) | May 2011 | positive

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. So...Read More

O
Livermore, CA | May 2010 | neutral

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 spectac...Read More

O
Dallas, TX | October 2006 | positive

My experience with this plant began while taking my dogs on their usual walk. All this spring I watched this little plant, which attract...Read More

C
Pocola, OK (Zone 7a) | November 2004 | negative

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

P
Deal, NJ (Zone 7a) | September 2004 | neutral

Very easy from seed.... direct sow after last frost or sow indoors........ However very prone to damping off....... Doesn't love to be t...Read More

N
Broadview, SK (Zone 3a) | September 2004 | positive

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...Read More

G
Sandstone, MN | September 2004 | positive

The leaves of this plant are quite spectacular, with irregular white patches that have a silvery sheen in the sunlight. Although some pe...Read More

A
A
| July 2004 | neutral

Spectular foliage when young, but becomes shabby with age. Self seeds. Thorns are long and will pierce thick clothing. Perhaps best grown...Read More

P
Westbrook, ME (Zone 5a) | November 2001 | neutral

This striking plant’s common name comes from the legend that Mary’s milk first made the white markings on the leaves. It is a biennia...Read More

Featured
Bald-faced Hornet
(Dolichovespula maculata)
Gang-gang Cockatoo
(Callocephalon fimbriatum)
Featured
Bald-faced Hornet
(Dolichovespula maculata)
Gang-gang Cockatoo
(Callocephalon fimbriatum)