Cirse, <em>Cirsium</em>: planting, growing, care

Description and botany

Genus Cirsium includes nearly 300 species and is commonly referred to as thistle. This generic term covers several spiny genera mostly belonging to the family Asteraceae (formerly Compositae) such as Carduus (thistle in the strict sense), Cynara (artichoke), Onopordum and Cirsium. The blue alpine thistle or sea holly (Eryngium alpinum) with its steel-blue tones belongs to the Apiaceae (umbellifers) like carrot, while the common teasel (Dipsacus fullonum), once used to card wool, is part of the Dipsacaceae. Thistles therefore form dense, compact heads that are either heads or umbels. They commonly grow on dry, poor ground while some Cirsium species such as rivulare prefer rich, fresh or even very wet soils.

Cirsium species are native to Eurasia and North America. These often large herbaceous plants are annual, biennial or perennial but short-lived. They grow very quickly and bear dense, nectar-rich inflorescences perched on long architectural stems. They produce numerous feathery seeds appreciated by birds such as goldfinches, contributing to plant dispersal that can be problematic in species like Cirsium arvense.

Distinction between genera Carduus and Cirsium is subtle. It is mainly based on the egrets of the fruits, also called pappus, which are composed of simple or denticulate hairs in true thistles and of feathery hairs in Cirsium.

Cirsium arvense – botanical illustration

Stems of Cirsium, like those of other thistles, are often winged and leaves are alternate and thorny. Cultivated forms often have fewer spines, as in Cirsium japonicum Rose Beauty, which is almost inermous. Ornamental Cirsium commonly reach 90 cm to 1.20 m in height with a spread of 50–60 cm depending on soil richness and moisture, unlike true thistles. Large leaves of 20–40 cm long are glabrous or pubescent, often dark or light bluish-green, entire to deeply lobed into narrow segments, with spiny, dentate margins. Plants first form a rosette of large leaves that sends up a sparsely leaved, ramified flowering stem ending in hirsute heads, 3 to 5 cm in diameter. Aerial parts dry off completely at season end before reappearing the following spring from the rhizomatous stump. Cirsium rivulare is slightly less running than Cirsium japonicum, which can spread up to 60 cm rather than 50.

Inflorescence consists only of tubular flowers in pink, purple, bluish or white tones, with presence of scales or tufts of hair between florets. They are borne in an involucre of spiny bracts, particularly decorative in Cirsium eriophorum, the wooly cirsium, which forms a wooly sphere about 5 cm across crowned with magenta florets. The whiteness of the head is very luminous in Cirsium rivulare Frosted Magic.

Fruit is an achene topped by a white, feathery egret that forms a silky decorative mass under frost. Cirsium arvense provides a food source for birds such as goldfinch and skylark, whose populations are declining.

Cirsium japonicum has medicinal properties known since Antiquity: anti-inflammatory, haemostatic, diuretic, anti-infective, etc. Its roots are eaten raw or cooked in Chinese cuisine. Young cooked leaves of Cirsium and the involucre of Cirsium oleraceum, the farmers’ cirsium or cabbage thistle, are eaten notably in northern and eastern France. Plant is rich in phosphorus. Common or field thistle (Cirsium arvense) grows in lush meadows suitable for beef cattle. Wooly cirsium is favourable for dairy cattle and cheese production (sheep grazing is not recommended on such land because droppings raise already high pH). Excessive presence of these Cirsium indicates an excess of organic matter and nitrogen fertiliser from overgrazing, which has the effect of immobilising phosphorus in calcareous soil.

Word “cirses” comes from Latin cirsion, which denoted a species of thistle reputed to fight varicose veins, called kirsos in Greek.

Main varieties of Cirsium

Varieties to plant

Cirsium rivulare Atropurpureum - Plume Thistle

Very hardy perennial with 3 cm bright pink pompon flowers, blooms all summer, perpetual, occasionally in September (remove spent flowers) and dark green foliage with few thorns. Plant in full sun in ordinary to very moist, heavy soils.

• Flowering time July to September
• Height at maturity 1,20 m

See the product sheet

Cirsium rivulare Frosted Magic

Riverside thistle variety with very bright white heads.

• Flowering time August, September
• Height at maturity 1,20 m

See the product sheet

Cirsium japonicum Rose Beauty - Japanese Thistl

Thistle with very few thorns and large hairy 5 cm heads from soft pink to magenta. Rustic wildflower, easy to grow in most rather dry soils and in full sun.

• Flowering time July to September
• Height at maturity 1 m

See the product sheet

Varieties to sow

Cirsium japonicum Pink and Rose Beauty - Japanese Thistle

Perennial plant from Japan with leaves that have few thorns, whose red and pink thistle flowers open in September–October. Easy to grow in all soils. Excellent cut flower.

• Flowering time October, November
• Height at maturity 1,20 m

See the product sheet

Planting

Where to plant thistles?

Requirements of thistles vary depending on species. Riverbank thistle prefers rather heavy, rather damp to very damp, rich soil since it grows along watercourses whereas Japanese thistle requires ordinary to dry, well-drained soil, even poor.

In both cases, full sun is recommended or at least a minimum of 6 hours’ sun per day. Their lifespan is fairly short but sowing occurs frequently if you omit cutting faded inflorescences.

When to plant?

Planting can be done in spring or autumn for better establishment.

How to plant?

This plant is very easy to grow if you respect each species’ soil moisture needs.

For planting your thistles :

• Dip rootball into a bucket of water to thoroughly moisten it.
• Loosen soil over a 50 cm width to encourage extension of rootstocks.
• Add organic amendment for species rivulare, which likes rich soils, such as well‑rotted leaf compost. For species japonicum, add sand or gravel or plant in a rock garden to make soil sufficiently well‑drained.
• Dig a hole the size of the rootball to insert it, taking care not to bury the collar. Space young plants 30 to 40 cm apart if you wish to form a full border; otherwise insert some young plants within a meadow.
• Replace soil and firm lightly.
• Water and mulch, especially species rivulare, to maintain cool soil.

Care

• Simply cut faded flowers between June and July, then allow fruits to form in the hope of obtaining some viable seeds.
• Stake young plant discreetly if strong winds blow.
• Divide Cirse every three years to rejuvenate young plant, which tends to weaken and die.
• Cirse des rives is sometimes affected by powdery mildew or “white disease” during drought or poor air circulation. Water root area well and mulch it from mid-spring. Cut surrounding foliage if air circulation is poor.

Propagation: division, sowing

Simplest propagation method is to separate rootstocks in spring or September or to sow seeds between February and June.

Division

• With a well-sharpened spade, separate peripheral rosettes.
• Lift them and replant elsewhere in loosened soil.

Sowing

• Sow Cirse from February to June indoors or directly outdoors.
• Fill a tray with good-quality seed compost.
• Sow seeds as thinly as possible, mixing with sand for better distribution.
• Cover seeds with 2–3 mm of sieved compost or vermiculite.
• Firm down lightly and water copiously with a fine spray.
• Place tray in light, avoiding direct sun, at temperature of 15°C to 20°C.

Seed germination will take 21 to 40 days.

• As soon as young plants reach height of 5 cm, pot them into buckets.
• Take care to harden off young plants over 15 days before planting permanently in garden in a very sunny spot in late spring or early autumn. Wait until end of May for temperature to be warm enough.

Early-season sowings will flower in first year. For later sowings, wait until following year to see flowers.

Uses and companion planting

You can flower a stream or pond bank, in cool soil with Cirsium rivulare which pairs with the erect, slender magenta spikes of loosestrife, with the marsh sage whose loose, slightly untidy clumps bear delicate sky-blue inflorescences, with airy meadow-rue in white, lemon-yellow or mauve, or with the small pale-pink star-shaped flowers of Lychnis flos-cuculi.

A natural planting idea: Cirsium rivulare ‘Atropurpureum’, Selinum wallichianum, Stipa tenuifolia and Sisyrinchium striatum, Geranium ‘Nimbus’, Allium christophii

Upright and wild thistles both add, without demanding care, a bit of spice to an otherwise dull meadow or natural garden. Their bold, sculptural clumps create rhythm and surprise with blue-green foliage topped by large purple or white heads that sway gently in a summer breeze.

Japanese thistle, fond of dry soil, pairs beautifully with the silvery foliage of lavender, cistus or santolina.

The Japanese thistle cultivar ‘Rose Beauty’, with very large heads, holds its own alongside Echinaceas and Rudbeckias, playing with colour and contrasting with more airy plants such as Gauras and bottle-brush grasses.

→ Discover other ideas for pairing thistles in our advice sheet!