Scotch thistle Onopordum acanthium

☠ Toxic to humans
🐾 Toxic to pets
🌸 Blooming
🍪 Not edible
‍🌱 Hard-care
cotton thistle
cotton thistle
cotton thistle
cotton thistle
cotton thistle
cotton thistle


The common name of Onopordum acanthium is Scotch thistle. This plant is easily recognized by its impressive spiny leaves and stems, which feature a silvery-gray color due to a thick layer of woolly hairs. The heavily armed leaves are large, lobed, and form a rosette at the base during the first year. In the following year, it produces a flowering stem that is also covered in spiky hairs. Scotch thistle produces a wealth of purple or occasionally white flower heads that are quite large and thistle-like, encased in a spiny involucre, which is a collection of bracts or scales subtending each flower head. The blooms have a somewhat fluffy appearance and attract a variety of pollinators, including bees and butterflies. After flowering, the plant generates a lot of seeds. These seeds are contained in small, dry, one-seeded fruits called achenes that have a tuft of hair called a pappus. This pappus aids in wind dispersal, helping the plant spread to new locations. The overall look of the Scotch thistle gives it a rather commanding and somewhat intimidating presence in the landscape, primarily due to its broad, spiky foliage, and prominent, attractive flower heads.

Plant Info
Common Problems

About this plant

  • memoNames

    • Family


    • Synonyms

      Cotton Thistle, Scotch Thistle, Scottish Thistle, Heraldic Thistle, Sliver Thistle.

    • Common names

      Onopordum acanthium L., Acanos spina Scop., Onopordon acanthium (L.) Lam., Onopordum alexandrinum Boiss., Onopordum acaulon L., Onopordum acaulon Gilib., Onopordum acanthium var. gautieri Rouy, Onopordum acanthium var. inermius Fiori, Onopordum acanthium L. var. thessalicum Fiori & Paol., Onopordum acanthium var. oligocephalum DC., Onopordum oligocephalum Clairv., Onopordum tauricum Willd., Onopordum acanthium var. acanthium.

  • skullToxicity

    • To humans

      Onopordum acanthium, commonly known as Scotch thistle, is not listed as toxic to humans. However, due to its spiky foliage and potential for skin irritation, it is not advisable to handle or ingest this plant. Consuming any part of non-toxic plants can still potentially cause mild stomach upset due to the plant's rough nature or personal sensitivities. There are no specific symptoms of poisoning associated with this plant, as it is not known to be poisonous.

    • To pets

      Scotch thistle is not specifically listed as toxic to pets. However, the spiny nature of the plant can cause physical injury to pets if they try to ingest or simply interact with the plant. The absence of known toxin does not mean it's safe for consumption, and pets may still experience gastrointestinal upset or mechanical injury if they ingest parts of this plant. It is always best to prevent pets from ingesting plants not intended for their consumption to avoid any potential complications.

  • infoCharacteristics

    • Life cycle


    • Foliage type


    • Color of leaves


    • Flower color


    • Height

      6-9 feet (1.8-2.7 meters)

    • Spread

      2-4 feet (0.6-1.2 meters)

    • Plant type


    • Hardiness zones


    • Native area



  • money-bagGeneral Benefits

    • Wildlife Attraction: Onopordum acanthium, commonly known as Scotch thistle, is known to attract bees, butterflies, and other beneficial pollinators, enhancing biodiversity.
    • Soil Improvement: The deep taproot of the Scotch thistle helps to break up compacted soil, which can improve soil structure and fertility over time.
    • Erosion Control: Its robust growth and extensive root system can help to stabilize soil and reduce erosion in certain environments.
    • Livestock Forage: Although it is often considered a weed, some farmers use Scotch thistle as emergency forage for livestock during drought conditions due to its resilience and availability.
    • Ornamental Use: With its striking appearance, the Scotch thistle can be used as an architectural plant in gardens, adding visual interest with its large, thistle-like flowers and spiny foliage.
    • Historical Emblem: The Scotch thistle is a national emblem of Scotland, symbolizing bravery, determination, and resilience, thus carrying cultural and historical significance.

  • medicalMedical Properties

    • Diuretic effect: Onopordum acanthium has been used traditionally to increase urine production which may help in the management of urinary tract conditions.
    • Anti-inflammatory properties: It is believed to contain compounds that may reduce inflammation, although more research is required to substantiate these claims.
    • Astringent: The plant has been used for its astringent properties to help with skin conditions and wounds, potentially aiding in the healing process.
    • Antimicrobial potential: There is some indication that the plant might have antimicrobial effects, although detailed studies are needed to validate this use.

  • windAir-purifying Qualities

    This plant is not specifically known for air purifying qualities.

  • leavesOther Uses

    • Fish Poison: The seeds of the Scotch thistle have been used historically by some indigenous groups to poison fish, making them easier to catch.
    • Natural Dye: The plant provides a natural dye, which can be extracted from its purple blooms and used for coloring textiles or inks.
    • Cardoon Substitute: Its stalks, when peeled and cooked, can sometimes be used as a substitute for cardoon in recipes.
    • Vegetation Management: The dense growth of Scotch thistle can be utilized for controlling erosion in some areas that are prone to soil degradation.
    • Ruminant Food: In some parts of the world, the leaves are used as a supplementary food for ruminant animals like sheep when other forage is scarce.
    • Symbolic Art: The imposing look of the Scotch thistle has been used symbolically in art and heraldry, representing nobility and protection.
    • Fiber Source: The stems of the Scotch thistle can be processed to extract fibers for making paper or craft materials.
    • Ecological Indicator: It can serve as an indicator species in certain environments, signaling overgrazing or disturbances in the ecosystem.
    • Biomass Fuel: Potentially, Scotch thistle could be harvested as a biomass crop for producing bioenergy, due to its ample bio-material.
    • Photography Subject: The strikingly architectural form of the Scotch thistle makes it a popular subject for photographers, especially during its bloom phase.

Interesting Facts

  • bedFeng Shui

    The Scots thistle is not used in Feng Shui practice.

  • aquariusZodiac Sign Compitability

    The Scots thistle is not used in astrology practice.

  • spiralPlant Symbolism

    • Defense: Onopordum acanthium, commonly known as Scotch thistle, is a plant covered with spiny leaves and stems, symbolizing protection and a prickly defense against enemies or harm.
    • Persistence: Scotch thistle has the ability to grow in harsh environments, demonstrating resilience and the strength to survive and even thrive under difficult conditions.
    • Nobility: The Scotch thistle is the national emblem of Scotland and is often associated with nobility and honor, reflecting its regal bearing and long-standing use in heraldry.
    • Determination: This tough plant can flourish in a variety of soils and climates, which represents a strong will and determination to overcome obstacles.

Every 2-3 weeks
2500 - 10000 Lux
Every 2-3 years
Spring to early summer
Not needed
  • water dropWater

    The Scotch Thistle needs moderate watering, usually once or twice a week depending on the weather and soil moisture. It's important to check the top inch of the soil; if it's dry, it's time to water. With their deep taproot system, they're fairly drought-tolerant once established. An adult plant typically requires around 1 to 1.5 gallons of water per week during the growing season. In the winter or cooler months, reduce the amount as the plant's water needs decrease.

  • sunLight

    Scotch Thistle thrives in full sunlight exposure for healthy growth. This plant prefers a location where it can receive at least 6 to 8 hours of direct sunlight each day. Avoid shady areas as insufficient light can lead to poor flowering and weak growth.

  • thermometerTemperature

    Scotch Thistle is hardy in a wide range of temperatures but grows best in conditions between 50°F and 75°F. The plant can tolerate temperatures as low as 20°F and as high as 90°F without significant damage.

  • scissorsPruning

    Pruning Scotch Thistle is not essential, but removing faded flowers can prevent unwanted self-seeding, which may lead to its invasive spread. The best time to prune is after flowering, usually late summer or early fall. Cutting back spent flowers will also encourage a tidier appearance.

  • broomCleaning

    As needed

  • bambooSoil

    Scots Thistle requires well-drained soil with a pH ranging from 6.0 to 8.0. A good soil mix can be created using equal parts of loam, sand, and peat, ensuring good drainage and aeration for the plant's roots. Amend with organic compost to provide nutrition.

  • plantRepotting

    Scots Thistle is typically a biennial plant and doesn't often require repotting. If grown in containers, repot every 2 to 3 years or when the plant outgrows its current pot, usually in late winter or early spring before new growth starts.

  • water dropsHumidity & Misting

    Scots Thistle tolerates a wide range of humidity levels but prefers dry conditions. Ensure there is good air circulation around the plant to prevent humidity from becoming too high.

  • pinSuitable locations

    • Indoor

      Ensure full sun, infrequent watering, and airy soil for indoor Scots Thistle growth.

    • Outdoor

      Plant in full sun, well-draining soil, and water sparingly for outdoor Scots Thistle.

    • Hardiness zone

      3-9 USDA

  • circleLife cycle

    The Scotch thistle (Onopordum acanthium) begins its life cycle when its seeds germinate, typically in the spring, after which it develops a rosette of leaves that can survive through the cold months. In its second year, it transitions to a rapid vegetative growth stage, where a tall stem can shoot up, reaching heights of up to 3 meters. During this stage, the plant produces large spiny leaves, and the stem is topped with a branching inflorescence. The flowering stage occurs in the summer of the second year, where the plant exhibits purple, globe-shaped flowers that attract a variety of pollinators. After pollination, the plant sets seeds which are then dispersed by wind, animals, or human activity. The Scotch thistle is a biennial plant, completing its life cycle within two years before dying, relying on the next generation of seeds to propagate the species.

  • sproutPropogation

    • Propogation time

      Spring to early summer

    • The most popular method of propagation for Onopordum acanthium, commonly known as Scotch thistle, is through seeds. Optimal seed sowing occurs in the fall, but spring sowing can also be successful. Seeds should be surface sown on well-draining soil and lightly covered with soil no more than 1/4 inch (about 6 millimeters) deep. It is important to keep the soil moist until germination, which usually happens within 2 to 3 weeks at temperatures between 55 to 65 degrees Fahrenheit (approximately 13 to 18 degrees Celsius). Once seedlings emerge and grow large enough to handle, they should be thinned or transplanted to allow ample space for growth, as Scotch thistle can become quite large and spiky.