How to Grow Scotch Thistle
Onopordum acanthium
Scotch Thistle is a hardy biennial — sow seed in late spring or early summer, let it form a large silver-woolly rosette in year one, then enjoy towering 2–3 m branching stems with purple thistle flowers in year two. Sow direct on well-drained, open ground in full sun; thin to 90 cm apart. No feeding needed on average soil. Drought-tolerant once established. Deadhead most spent heads to control spread, but leave a few to self-seed for a continuous succession. Wear gloves — all parts are spiny.
When to Start
Direct sow outdoors as soon as soil reaches 5°C — typically early to mid spring. Hardy enough to tolerate light frosts.
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Growth Stages
Approximate days from start
Care Essentials
- Onopordum is a lean feeder — no feeding is needed on average garden soil. On very poor or sandy soils, a single light balanced dressing at transplanting encourages strong first-year rosettes.
- A dramatic architectural biennial reaching 2–3 m in its second year, with huge silver-white woolly leaves and wings running up the branching stems. Purple thistle flower heads appear from midsummer. Hardy and drought-tolerant once established; self-seeds freely on bare or disturbed soil. Superb at the back of a border or as a specimen. Gloves recommended — all parts are spiny.
Growing Conditions
- Min. soil temperature
- 5°C+
- Germination temperature
- 10–20°C
- Direct sow
- —
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Spacing & Planting
| Plant spacing | 90 cm |
| Row spacing | 100 cm |
| Sow depth | 1 cm |
| Mature height | 250 cm |
| Mature spread | 90 cm |
Growing Conditions
| Min. soil temperature | 5°C |
| Germination temperature | 10–20°C |
| Base growth temperature | 4°C |
| Min. daylength to start | 10h |
| Photoperiod sensitivity | day neutral |
Frequently Asked Questions
- How far apart should I plant Scotch Thistle?
- Plant Scotch Thistle 90cm apart with 100cm between rows.
- Is Scotch Thistle frost hardy?
- Scotch Thistle is classified as Hardy.
