Members of the Silybum plant genus are hardy annuals or biennials. They can reach a height of about 1.2 m (4 feet).
They bloom in the summer, when they carry purple flowers reminiscent of thistles.
Some common names for Silybum include Milk Thistle, Lady's Thistle, Holy thistle, and Our Lady's Milk Thistle.
Common Names: Milk Thistle, Holy Thistle, Elephant Thistle, Ivory Thistle, Blessed Milk Thistle.
Life Cycle: Hardy annual. Hardy biennial.
Height: 16 to 80 inches (40 to 200 cm).
Native: Europe, Mediterranean, Middle East, Northern Africa.
Growing Region: Zones 1 to 10.
When starting off outdoors, the seeds of Silybum species such as milk thistle should be sown at a depth of 3 mm (1/8th inch). Do so either in early summer (Silybum biennials) or just after the last frost of spring (annual Silybum).
Milk thistles can grow in either sunny or lightly shaded areas of the garden. The soil type is not to important.
If starting Milk thistle off indoors, then do so about two months before they are due to be transplanted outdoors. Transplant biennials in late summer, and annuals following the last frost of spring.
It takes about three weeks for milk thistle to germinate at a temperature of 12 to 15 degrees centigrade (54 to 59°F).
It is easy to look after Milk thistle and other members of the Silybum plant genus. They readily tolerate dry ands wet soils, so just let them be.
They may however become weedy, so it is best to deadhead the flowers before they set seed, and to remove any unwanted thistle plants.