Silybum Plant Growing & Care Guide for Gardeners

Article by Dean Ravenscroft, Ph.D. - Updated 27th Oct 2023

In this Gardener's HQ guide, we'll explore cultivating Silybum plants in your garden, indoor spaces, and other settings.

Milk Thistle, Ivory Thistle: Cultivation & Garden Use

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

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).

Silybum - Milk Thistle by Andrusdevelopment; Creative Commons.

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.

Common Questions

How many members does the Silybum genus have?

The Silybum genus comprises of 2 known species, with Silybum marianum, or Milk Thistle, being the most well-known.

Do members of Silybum make a good garden or landscaping plant?

Silybum is not typically used in general landscaping due to its spiny nature, but it can add interest to wildlife gardens.

Which Silybum species are most frequently grown by gardeners?

Silybum marianum (Milk Thistle) is commonly grown, both for its intriguing appearance and its medicinal properties.

Are members of the Silybum plant genus fragrant?

Silybum plants are not typically known for their fragrance.

What is the perfect location to grow Silybum?

Silybum species prefer full sun and well-drained soils. They are quite tolerant of poor soils and dry conditions.

Is Silybum invasive in the USA, if so in which states?

Currently, Silybum marianum is considered invasive in parts of the USA, especially in the western states. Check local regulations for updated information.

How do I remove Silybum plants from my garden?

To remove Silybum, dig up the entire plant, making sure to remove all root fragments. Be cautious of its spiny leaves.

Summary

The Silybum genus consists of annual or biennial plants native to the Mediterranean region. They are recognized for their glossy green, spiny leaves with white veins and large, purple, thistle-like flowers. The seeds of Silybum marianum are used in herbal medicine.

Silybum can be grown from seeds, sown in spring or autumn. They prefer full sun and thrive in a variety of soil types, including poor, dry soils. Once established, they require minimal watering and are quite drought-tolerant. Note that they can become invasive in some areas.

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.