Cotton thistle (Onopordum acanthium) is a plant in the annuals and biennials category that can grow 3m – 8m tall and 50cm – 1.5m wide. In this growing guide we’ll learn the cultivation details and how to plant Cotton thistle (Onopordum acanthium).
This plant has several common names including: cotton thistle, Argentine thistle, down thistle, giant thistle, musk thistle, oak thistle, oat thistle, Queen Mary’s thistle, Scotch thistle, Scots thistle, silver thistle, star thistle or thistle-upon-thistle.
This is a deciduous plant that takes 2-5 years to reach full maturity.
In this article
Plant profile
Common name: cotton thistle, Argentine thistle, down thistle, giant thistle, musk thistle, oak thistle, oat thistle, Queen Mary’s thistle, Scotch thistle, Scots thistle, silver thistle, star thistle, thistle-upon-thistle
Scientific name: Onopordum acanthium
Plant type: Annual / Biennial
Habit: Bushy
Height: 3m – 8m
Spread: 50cm – 1.5m
Foliage: Deciduous
Sunlight: Full Sun
Soil: Chalk, Loam, Sand
Moisture: Well drained
Garden type: Informal Garden, Wildflower meadow
Planting type: Flower borders and bedding
Other characteristics: Plants for pollinators
Seasonal colors
| Season | Stem | Foliage | Flower | Fruit |
|---|---|---|---|---|
| Spring | ||||
| Summer | ||||
| Autumn | ||||
| Winter |
How to plant Cotton thistle (Onopordum acanthium) – Agnieszka KwiecieĊ, Nova, CC BY-SA 4.0, via Wikimedia Commons
Annuals and biennials are ideal for formal or informal flower beds, but also for growing in pots and containers of all kinds. They are important plants for their rapid growth, instant color and relatively low cost.
They are also useful plants for filling spaces between newly planted trees and shrubs, as well as in perennial beds that may need to be revived after the first spring bloom.
They are an important ingredient in country house gardens and wildflower meadows.
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How to plant
In this section we will learn how to plant Cotton thistle (Onopordum acanthium), know its needs in terms of soil, watering and sun exposure.
Soil
Cotton thistle (Onopordum acanthium) is not a demanding plant regarding the type of soil and can grow in chalk, loam or sand.
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The chalky soil is pale and contains chunks of calcium-rich rock. It is a fertile and well-draining soil, almost always alkaline.
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The loam soil is dark, rich in organic matter but balanced in minerals. It offers the best of all worlds, retaining enough water for the plants, but allowing excess moisture to drain away. This is the most desired type of garden soil, perfect for most plants.
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Sandy soil is light, porous and very easy to drain. It is a soil poor in organic matter and nutrients. It is composed of relatively large mineral particles that allow water to drain quickly.
As for pH, it is a plant that grows ideally in soils with pH alkaline or neutral.
Regarding drainage, Onopordum acanthium likes to grow in well drained soil.
Sunlight
Cotton thistle (Onopordum acanthium) should be grown in full sun places.
Cultivation profiles – Growing Cotton thistle (Onopordum acanthium) – Stefan.lefnaer, CC BY-SA 4.0, via Wikimedia Commons
