How to Grow Silybum Plants

Guide to Growing Milk Thistle, Ivory Thistle and Holy Thistle

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.

Silybum marianum
Silybum marianum – Blessed Milk Thistle by -Merce-; Creative Commons.

Milk Thistle
Silybum - Milk Thistle by Andrusdevelopment; Creative Commons.

Silybum Plant Growing and Care Guide

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.

Flowers: Summer.
Flower Details: Pink/red-purple, white. Tubular florets. Thistle-like.
Foliage: Alternative. Lobed. Oblong. Lanceolate. Spiny. Prickly. Mottled. Contain milky sap.

Sow Outside: 1/8 inch (3 mm). Annuals: Following the last frost. biennials: Beginning of summer. Spacing 16 to 36 inches (40 to 90 cm).
Sow Inside: Germination time: two to three weeks. Temperature 60°F (16°C). Seven or eight weeks in advance. Transplant annuals outdoors following the last frost. Transplant biennials outdoors towards the end of summer or in the first month of autumn.

Requirements: Full sunlight or light shade. Good drainage. Most soils. Rich soil if growing for foliage. Can survive in dry soils. Prone to damping off.
Family: Asteraceae.
Miscellaneous: Often grown for its foliage. Seeds have been used for thousands of years in traditional medication for the treatment of liver disease.

How to Grow Milk Thistle and other Silybum Plants in the Garden

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).

Caring for Milk Thistle (Silybum)

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.

I hope that you enjoyed this guide on how to grow Silybum plants. You may also enjoy the following Gardener's HQ growing guides: How to grow Echinacea purpurea and Brachycome plants.