<em>Petasites</em>: planting, cultivation, care

Description and botany

Petasite is a rhizomatous perennial plant of family Asteraceae, like daisy and aster. It grows naturally on riverbanks, in wet ditches and understoreys, and up to about 1 500 m altitude in northern Europe, particularly in France, but also in Asia, North Africa and North America.

Genus includes around fifteen species some of which, such as Petasites hybridus (syn. Petasites officinalis), are so common that they are often found on ditch edges, near wet places or in mountainous areas of our country which they readily colonise.

Among petasites, one distinguishes small-leaved species such as Petasites fragrans which is scented, large-leaved species such as Petasites albus or white petasite and giant species such as giant Japanese petasites (Petasites japonicus var. Giganteus) and Petasites hybridus, also called great petasite or hybrid petasite. The latter, which is also a recognised medicinal plant, bears many common nicknames such as “Hatter”, “Great donkey’s step”, “Devil’s hat”, “scabwort”, “pest-herb” or “marsh rhubarb”.

Petasite is also sometimes encountered under English name “butterbur”, because its huge leaves were once used to wrap lumps of butter.

Fast-growing, all petasites form dense, mat-forming clumps. Depending on species, plant height ranges from 0.30 to 0.50 m for groundcovers up to 1.50 m for the huge petasite specimens. But even the shortest petasites can easily reach more than 1 m spread at maturity. This perennial spreads easily, often extending well beyond intended limits thanks to its thick running rhizomes, and can become invasive if its spread is not controlled.

Petasite hybridus – botanical illustration

Petasite is mainly grown for its large luxuriant leaves, as its flowering is not very showy. Flowering usually occurs before the foliage in late winter. From March to May, depending on climate and sometimes earlier, the flowering stalks held erect and often purple, emerge at ground level before the new basal leaves. They open in ovoid terminal clusters composed of small heads 1 to 2 cm in diameter. Each head comprises numerous tubular flowers ending in five teeth and peripheral ligulate florets extended by a long petal. Petasite is a dioecious plant, meaning there are female and male plants which differ by the shape of these florets, more or less elongated. These heads are surrounded by bracts of pale green or purple depending on species.

These globular, compact inflorescences, borne on leafy stems, are 10 to 25 cm high, sometimes truly colossal in giant petasites.

Rosy, purplish (Petasites hybridus), white (Petasites albus) or creamy-white, they are fragrant and give off a delightful sweet vanilla scent. Rich in nectar, they attract hungry pollinating insects in mid-winter.

Flowering is followed by appearance of vigorous and spectacular vegetation. The foliage is the main attraction of this majestic groundcover. Deciduous, this foliage dies back in winter and only reappears fairly late in spring well after the flower heads. In April, from the powerful underground rhizome, basal rosettes of leaves borne on a long petiole begin to emerge. The plant then produces a generous clump of leaves of varying size according to species and varieties. These spectacular leaves grow over weeks to become gigantic by early summer.

Petasite leaves are characterised by their reniform (kidney-shaped) to cordate (heart-shaped) form, reaching 6 cm for Petasites fragrans up to 1 metre in diameter for giant species such as Petasites japonicus var. giganteus and Petasites hybridus, which are the true “hatters”! Indeed, Petasite owes its name to its rounded lamina, “petasos” in Greek referring to the broad-brimmed round hat worn by Greek shepherds.

Leaves have more or less regularly dentate margins and a pubescent underside and sometimes a wooly upper surface with greyish-green tones. Supple and downy, this foliage shows beautiful shades of green from . Some forms display splendid irregular variegation of golden yellow as in Petasites hybridus ‘Variegatus’.

By late summer, foliage of large petasites becomes so abundant that it often develops to the point of smothering other nearby plants, leaving them little chance of survival.

With good hardiness down to at least −25°C, petasite establishes itself in many parts of our country, except perhaps in Mediterranean climates that are too dry in summer. While it tolerates various soil types whether calcareous, neutral or acidic (except stony soils), it prefers a rich, constantly cool or even very wet woodland soil.

Development of an inflorescence of Petasites hybridus

It is a shade or partial-shade and cool-loving plant, ideal for giving a wild look in a shade garden, near water features or on the edge of damp woodlands where it can form stands of greenery sometimes over 1 m high on its own. It is also perfect as a groundcover at the border, middle or back of semi-shaded beds where it brings an exotic lushness.

Petasite has medicinal properties recognised for centuries. From its leaves or rhizomes, an extract free of the plant’s naturally occurring toxic substances is obtained. It is used to relieve migraines and reduce symptoms of allergic rhinitis. In the 17th century it was prescribed for coughs, asthma and to treat wounds and burns.

In Japan, the long petioles of Petasites japonicus are eaten as vegetables.

Main species and varieties

The genus includes around fifteen species that differ mainly in the size of their leaves, ranging from 6 cm to 1 m in diameter, and in the colour of their flowers.

Most popular

Petasites hybridus

This is the Great petasite! Its fragrant flowering is followed by the emergence of very large heart-shaped leaves reaching 50 cm to 1 metre in diameter! It brings a lush touch to a very damp understorey or to large somewhat neglected areas of the garden that it can colonise with ease!

• Flowering time April, May
• Height at maturity 50 cm

See the product sheet

Our favourites

Petasites albus

It is also called white petasite and, like all petasites, it is capable of spreading up to 1.5 m in span at ripeness. It is particularly useful to bring a touch of exoticism and light to damp, inhospitable areas of a large garden.

• Flowering time April to June
• Height at maturity 40 cm

See the product sheet

Planting

Where to plant petasite?

Hardy down to -25°C, petasite establishes itself throughout France, except perhaps in Mediterranean regions, too hot and dry in summer, because it favours shaded areas and cool, moist soils that retain water well. It will tolerate summer heat provided soil remains consistently moist and cool at depth in summer, because petasite does not like drought.

It thrives in shade or partial shade, sheltered from scorching sun, under the foliage of deciduous trees that will give it the coolness it needs.

Undemanding about soil type, provided it is cool, moist, even waterlogged, it nevertheless prefers soil rich in organic matter, light, in which it will develop with remarkable vigour. It will also grow very well in heavy clay soil.

Before planting, remember that the petasite can be invasive because once established it will spread without regard for its neighbours… It is perfect for occupying large areas. If you want to control its growth, plant it in dry soil in partial shade where sun predominates over shade; it will be much less vigorous and rampant there while still keeping an attractive presence!

It is the ideal plant for a water garden and a shade garden, for understorey planting or a wet meadow. It is perfect for colonising soil of a cool understorey, damp riverbanks, the edge of a pond or an ornamental pond. It is useful for limiting adventive weeds in the most unwelcoming, very wet corners or marshy zones of a large garden. In smaller spaces, its propensity to spread must be contained because it nibbles into the ground, ignoring boundaries.

When to plant petasite?

Planting petasite can be done either in spring, from March to May, or in autumn from September to November.

How to plant petasite?

As you have understood, the petasite has a robust vigour but can be invasive! Space plantings well: at ripeness, a single specimen will easily reach a spread of 1 m. Do not be misled by its small size on receipt of your bucket! Allow 3 plants per m² and water until establishment and throughout first year: it needs plenty of water to settle in.

• Dig a hole 2 to 3 times wider than the rootball
• Spade soil deeply
• Add a good shovelful of well-rotted compost or manure
• Backfill and firm down
• Water generously
• Mulch around plant to retain moisture during summer

If you wish to limit expansion of its running rootstocks you can also try containing it in a closed basket. Discover our detailed explanations in this step-by-step: limiting an invasive plant.

Care and maintenance

Pétasite is not a delicate plant, it requires almost no maintenance and is free from disease.

Keep soil moist: it forms large exotic-style displays until frost, but water frequently and generously as it must never lack water. Mulch in May to reduce watering and evaporation.

Pétasite often exceeds expectations, so to prevent it becoming invasive, each spring after flowering, cut around the base with a spade to remove wandering rootstocks that would spread too far.

Every two years in spring, if desired, spread a few shovelfuls of compost over the stump.

Multiplication

Petasite has a natural tendency to spread rapidly. However, to obtain new young plants we recommend dividing in spring or autumn, after flowering, or propagating the rootstocks.petasite has a natural tendency to spread rapidly. However, to obtain new young plants we recommend dividing in spring or autumn, after flowering, or propagating the rootstocks.

Division

• Using a spade, dig up part of the stump
• With a spade, recover pieces of rootstock each bearing at least two leafy shoots
• Replant these pieces immediately in cool soil enriched with compost
• Water copiously to keep soil moist

Making cuttings of petasite

Simply cut fragments of rootstock about 10 cm long bearing 1 or 2 buds and push them into moist soil so they root quickly.

Companion planting Petasites in the garden

With its oversized leaves and softly coloured flowers, Petasite is a must-have perennial in shade gardens and at the water’s edge. Whether more than 1 m tall or groundcover, it fits into all shaded settings in large drifts under trees as well as in a cool rockery. Although it easily holds its own, it lends itself to lush combinations with other perennials for wet banks or perennials for cool shade.

Example pairing: Matteucia struthiopteris, Astilbe japonica ‘Deutschland’, Euphorbia palustris and Petasite hybridus

At water’s edge, pair it with Gunnera, Rodgersias or darmera, goat’s beard, marsh euphorbias and graceful astilbes, Meadowsweet, lysimachias, knotweeds…

At edge of a cool, damp woodland, in a “jungle” spirit, it will form luxuriant vegetative masses surrounded by shade companions such as hostas and ferns.

In a naturalistic garden at the edge or centre of a shaded border, it will be an attractive partner for Solomon’s seals, Veronicastrum virginicum, ligularias and Silver Candles.

It will also look splendid alongside Asian primulas or the hardy begonia grandis evansiana.

As its foliage reappears fairly late in spring, pair it with spring bulbs such as spring snowflakes, chionodoxa, crocus, hyacinths or iris reticula, Galanthus, which will occupy space in late winter before Petasite leaves reach their characteristic size!