Marsh thistle

How to recognise it

Habit

Biennial: in the first year a leaf rosette, in the second an upright, little-branched stem of 0.5–2 m.

Leaf

Deeply divided, with numerous spines along the edge; dark green above, often with a purplish margin, cobwebby-hairy below.

Stem

Covered from bottom to top with continuous spiny wings; often dark or purple-tinged.

Flower

In June–September small heads of 1–1.5 cm, dark purple, sometimes white, in tight clusters at the top of the stem and side branches.

Fruit

A small nut with a white, feathery pappus that blows away on the wind.

Confused with

Creeping thistle has a stem without wings or spines. Spear thistle has larger, egg-shaped heads, leaves with a long terminal spine and grows on drier ground. Welted thistle has larger, less tightly packed heads and a pappus without feathery hairs.

Flowering: June–September · Pruning: September

Why grow it?

• A rich source of nectar in summer for bumblebees, wild bees, hoverflies and butterflies.
• Goldfinches and other seed-eaters eat the ripe seed.
• A slender, upright plant that gives structure to a wet wildflower meadow or pond edge without taking up much room.
• Not invasive: it has no creeping roots and dies after flowering.
• In winter the green rosette and the dead stems remain, giving shelter to insects.

Marsh thistle: where does it grow best?

• In the wild: wet hay meadows, marshes, reedbeds, ditch banks, riversides, damp woodland edges and clearings.
• Sun to partial shade.
• Moist to wet, moderately rich soil: sand, loam, clay or peat, preferably slightly acid to neutral.
• In the garden: at the edge of a pond, in a wet wildflower meadow or in a damp, wild corner.

Goes well with

• Ragged-robin: Pink flowers in May–June in the same wet hay meadow.
• Meadowsweet: Creamy, fragrant plumes in summer on wet soil.
• Purple loosestrife: Purple spikes at the water’s edge, also loved by bees.
• Hemp-agrimony: A butterfly magnet in late summer on the same damp soil.

Marsh thistle: when and how to plant it?

1. Buy seed or young plants from a nursery specialising in native plants. Never dig up plants from the wild.
2. Sow in September–October or in March where it is to grow, on bare, damp soil, barely covering the seed.
3. Thin out or plant young rosettes 40–50 cm apart.
4. Plant out pot-grown plants while young, in autumn or spring: a larger taproot does not transplant well.
5. Keep the soil moist until the plants are established.
6. Sow or plant two years running so there are flowering plants every year.

Care

Water

Not needed in a wet spot. In a damp spot only during long dry spells.

Feeding

Not needed.

Mowing

Mow a wet hay meadow in September, after seed set. Mowing as early as June removes the flowering stems.

Let it seed

Let some of the heads ripen so that new rosettes appear.

Limiting self-seeding

Cut off some of the spent heads before they turn fluffy if you want fewer seedlings.

Tip: Put marsh thistle at the back, at the pond edge or in a wet meadow: its tall, narrow silhouette takes up little room, and from the patio you can watch the butterflies and goldfinches.

Pruning and mowing

Pruning months: September.

When: After seed set, in September; the plant dies by itself after flowering.

How:

• Let some of the heads ripen for the birds and for new seedlings.
• Cut off the other spent heads before they turn fluffy.
• Feel free to leave the dead stems standing until spring: insects find shelter there.
• Then cut them down at ground level.

Caution: Wear sturdy gloves and long sleeves: the whole stem is covered in spines.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow in autumn or early spring on bare, damp soil. The plant flowers the following year.

Self-seeding

In an open, damp spot it self-seeds; you can move young rosettes in autumn.

Marsh thistle: how does it get through the winter?

Hardy to −30 °C.

• The first-year rosette stays green and lies flat on the ground.
• Fully hardy.
• The dead stems stay standing into winter; they give structure and shelter insects.

Diseases and pests

• Too many seedlings: Cut off most heads before the seed is ripe and dig out unwanted rosettes in spring.
• Aphids: Sometimes on the stem tips. Ladybirds and hoverfly larvae do the job.
• Drought: In a dry spot it stays small and disappears. Choose a damp spot.
• Gone after flowering: That is normal: it is a biennial. Let it seed and keep some bare ground.
• Spines: Do not plant it next to a path or seating area.

Through the year

• March: Sow where it is to grow. Rosettes start growing.
• May: The flowering stem shoots up.
• June: Flowering begins.
• July: Full flower; bumblebees and butterflies on the flowers.
• August: Seed ripens; goldfinches on the heads.
• September: Mow after seed set. Sow for next year.
• October: New rosettes. Plant pot-grown plants.
• December: Dead stems and green rosettes.

Did you know?

• Palustre comes from the Latin ‘palus’, marsh: a reference to its wet habitats.
• There is a white-flowered form, which you occasionally see among the purple plants.
• Unlike creeping thistle, marsh thistle does not spread aggressively: after flowering the plant dies and only the seed produces a new generation.