• AGM plants

    AGM plants have been through a rigorous trial and assessment programme. They are:

    • Excellent for ordinary use in appropriate conditions
    • Available to buy
    • Of good constitution
    • Essentially stable in form & colour
    • Reasonably resistant to pests & diseases

Petasites japonicus

giant butterbur

  • Other common names giant butterbur

  • Family Asteraceae

  • Genus Petasites are perennial plants, usually large, with thick rhizomes or stems. Leaves are often very large and either heart-shaped or kidney-shaded. Scapes or stems many-headed, with any leaves usually reduced to scales. Flowers dioecious in usually rayless heads, purple or white, rarely yellowish, borne in panicles or racemes at the ends of the scapes

  • Details P. japonicus is a substantial plant, producing huge suborbicular leaves to 90cm across, reaching 150cm in height, in summer. Flowers are cream to white, borne in February on stout erect stems to 30cm. The plant normally available is nearly always the male plant

  • Plant range Korea China Japan


  • Foliage Deciduous

  • Habit Bushy

  • Hardiness

    Hardiness ratings

    All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

    • H1a - Under glass all year (>15C)
    • H1b - Can be grown outside in the summer (10 - 15)
    • H1c - Can be grown outside in the summer (5 - 10)
    • H2 - Tolerant of low temperatures, but not surviving being frozen (1 to 5)
    • H3 - Hardy in coastal and relatively mild parts of the UK (-5 to 1)
    • H4 - Hardy through most of the UK (-10 to -5)
    • H5 - Hardy in most places throughout the UK even in severe winters (-15 to -10)
    • H6 - Hardy in all of UK and northern Europe (-20 to -15)
    • H7 - Hardy in the severest European continental climates (< -20)




  • Full Shade

  • Partial Shade

  • Aspect North-facing or East-facing

  • Exposure Sheltered


  • Clay


  • Loam


  • MoisturePoorly-drained, Moist but well-drained

  • SoilClay, Loam

  • pHAcid, Alkaline, Neutral


  • Ultimate height 1-1.5 metres

  • Ultimate spread 4-8 metres

  • Time to ultimate height 2-5 years

How to grow

Cultivation Grow in deep humus-rich, fertile soil that is permanently moist but not stagnant, in partial or full shade. It may become invasive

Propagation Divide in spring

Suggested planting locations and garden types Low Maintenance Wildlife Gardens

How to care

Pruning Remove the old foliage before the onset of new growth in late winter

Pests Generally trouble free

Diseases Generally trouble free

Did you find the information you were looking for?

RHS members can get exclusive individual advice from the RHS Gardening Advice team.

Join the RHS now

Get involved

The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.