Tall biennial or annual thistle with marbled leaves and pink-purple flower heads. Seeds yield silymarin, the most studied plant compound for liver support.
Hardiness ratings
| System | Rating | Temperature range | How to read it |
|---|---|---|---|
| USDA hardiness zone | Zone 5–9 | −28.9 °C to −1.1 °C | Zones where it can be grown as an annual — not a frost-tolerance rating |
| RHS hardiness rating | H7 | down to −20 °C | Plant needs at least this level of cold tolerance |
| Canadian plant hardiness zone | Zone 5–9 | −23 °C and warmer | Zones where it can be grown as an annual — not a frost-tolerance rating |
| Australian (ANBG) zone | Zone 1–5 | −15 °C to 10 °C | Zones where it can be grown as an annual — not a frost-tolerance rating |
As a tender annual, Milk thistle doesn't overwinter — the zone range shows where the growing season supports it. See the RHS rating for its actual cold tolerance.
Growing notes
- Self-seeds heavily — single plant produces hundreds of seeds and can become a weed
- Declared invasive in several Australian states — check local rules before planting
- Always consult a qualified medical or herbal practitioner before using any plant medicinally
Categories
Related plants
Cross-check Milk thistle against your zones