Petasites japonicus var. giganteus - Giant Butterbur, Bog Plant

Petasites japonicus subsp. giganteus (widely sold as var. giganteus), known as giant butterbur, is a huge foliage plant for large, damp gardens. Its nearly round leaves, up to about 90 cm across, stand on strong, ribbed stalks. In late winter and early spring, before the leaves, it produces dense, rounded clusters of cream to greenish-white flowers close to the ground, which give early nectar for insects.

Giant butterbur at a glance

Botanical name	Petasites japonicus subsp. giganteus (syn. P. japonicus var. giganteus)
Common name	Giant butterbur
Plant type	Very large, spreading perennial; dies back in winter
Height and spread	About 1–1.5 m tall; spreads 4–8 m by underground stems
Flowers	Cream to greenish-white, in dense rounded clusters near the ground before the leaves, February to April
Position	Part shade or shade
Soil	Deep, humus-rich soil that stays moist but not stagnant
Pond depth	None – moist soil, not water
Hardiness	RHS H6 – hardy in a very cold winter (-20 to -15°C)
Native to	Not UK native

Is giant butterbur a pond plant?

No. It is a bog and moist-soil plant, not a water plant. Plant it in deep, permanently moist soil beside water, not in the water itself.

Is giant butterbur invasive?

Yes, it can be. The RHS gives a spread of 4–8 m and calls it a potential nuisance. The BSBI says it is invasive in some areas, and the GB Non-Native Species Secretariat records it shading out native riverbank plants, with tough rhizomes that are hard to remove. It is legal to buy and grow in a garden (in Scotland it is an offence to plant it in the wild), but plant it only in a large garden where it can be contained, never beside rivers, streams or natural ponds, and never dump garden waste containing it.

Is it poisonous?

Yes. It is not edible. It contains pyrrolizidine alkaloids, which are linked to liver damage, and petasitenine, which can cause cancer.

Which size should I buy?

Bare-root plants (7 cm, 9 cm, 1 litre and 3 litre) arrive without a pot or compost and are the most economical way to plant a group. Potted plants (9 cm, 1 litre and 3 litre) arrive growing in our peat-free compost and give a faster display. Packs of 3 come in 7 cm, 9 cm, 1 litre and 3 litre bare-root sizes and cost less per plant. The 2x Pot & Compost option is two plants supplied with pots and compost.