Is it really from Scotland?

Despite its common name, it is actually native to Europe and western Asia.

The best method is to remove the plant before it sets seed.

Plant guide

Cotton thistle.

Onopordum acanthium L.

Pronounced on-oh-POR-dum ah-KAN-thee-um

Also known as Cotton Thistle, Cotton-thistle, Giant Thistle, Heraldic Thistle

The cotton thistle is a striking biennial plant known for its dramatic architectural presence and silvery, woolly foliage. It produces impressive purple flower heads that attract plenty of pollinators to your garden. You will find it makes a bold statement in any sunny landscape.

Another photo of Cotton thistle — Photo by Matt Lavin (CC BY) via iNaturalist

At a glance

Care level: Easy
Plant type: Biennial
Light: Full sun
Indoor light: Direct sun
Water: Every 7 to 14 days
Mature size: 6 to 8 feet tall
Growth rate: Fast
Hardiness: USDA 3 to 9
Bloom time: Mid to late summer

Care

Plant this beauty in a spot with plenty of sun and well draining soil. Keep an eye out for aphids or mildew if the air circulation is poor. It is a biennial, so it will grow leaves the first year and bloom the second before dying back.

Watering: Water deeply once established, but allow the soil to dry out between sessions.
Feeding: Feed with a balanced fertilizer during the first year of growth to support foliage development.
Pruning: Remove spent flower stalks after they finish blooming to prevent unwanted self seeding.
Repotting: Since it is a biennial, you likely will not need to repot it unless you are starting it in a container.
Soil: Well draining, sandy or loamy soil
Soil pH: Neutral to slightly alkaline
Temperature: -25 to 35°C
Humidity: 20 to 50%
Drought tolerance: High
Lifespan: Biennial, typically 2 years
Fragrance: Light
Deer and rabbits: High

Safety

People: There is no significant toxicity, but the sharp spines pose a physical injury risk.
Children: Keep children away due to the extremely sharp and painful spines covering the entire plant.
Contact allergens: The stiff, sharp spines can cause skin punctures and irritation.
Airborne allergens: The fine hairs on the leaves can become airborne and irritate the respiratory tract.
Edibility: The plant is not considered edible and should be avoided for consumption.

How to identify it

Silvery white woolly foliage
Large spiny leaves
Tall branching stems
Purple thistle like flower heads

Height: 1.5 to 3m
Spread: 0.6 to 1.2m
Leaves: gray, silver, deciduous
Flowers: purple, pink, 3 to 6cm
Fruit: brown, Autumn

Problems to watch for

Powdery MildewCommon
RustCommon
AphidsUncommon
Slugs and SnailsUncommon

By symptom

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Growing it

Propagation: seed
When to plant: spring, autumn
Overwintering: The first year rosette stays low to the ground and requires no special protection.
In containers: It is generally too large and aggressive for standard containers.

Direct Sowing

1. Collect seeds in late autumn.
2. Sow directly into well drained soil in a sunny spot.
3. Thin seedlings to allow for large growth.

Plant in a location where you can easily reach the base to remove it before it spreads.

Grows well with

Mullein — They share similar requirements for dry, sunny, disturbed soil.
Common Sage — It complements the silver foliage and thrives in similar conditions.

Similar species

Milk Thistle — It has similar spiny foliage but features distinctive white marbling on the leaves.

Science

Family: Asteraceae
Genus: Onopordum
Order: Asterales
Class: Magnoliopsida
Native range: Europe and western Asia
Conservation: It is considered an invasive weed in many parts of the world, including North America and Australia.

It thrives in disturbed, dry, sunny soils where it can outcompete native vegetation.

Value to wildlife: nectar source, seed source for birds
Pollinators: bees, butterflies
Uses: ornamental architectural plant, dried flower arrangements

Through the year

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Flowering

Fruiting

Foliage

Ecological indicators

Salinity: 2/9
Soil reaction: 6/9
Light: 8/9
Temperature: 5/9
Moisture: 2/9
Nutrients: 5/9

Taxonomy resolved against GBIF.

Questions people ask

Is it really from Scotland?: Despite its common name, it is actually native to Europe and western Asia.
How do I control it?: The best method is to remove the plant before it sets seed.

Where the name comes from

The genus name Onopordum comes from Greek words meaning donkey and fart, referring to the plant's effect on donkeys, while acanthium refers to its prickly nature.

Good to know

It is the national emblem of Scotland.
The plant can produce over 20,000 seeds in a single season.
It is often called the heraldic thistle.

Also in

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This guide was generated with AI and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.