• 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

Butomus umbellatus

flowering rush

flowering rush

© RHS 2002

  • Other common names flowering rush
    grassy rush

    lily grass
    water gladiolus

    see more
  • Family Butomaceae

  • Genus Butomus are submerged rhizomatous perennials with narrowly strap-shaped leaves and 6-petalled pink flowers held in umbels well above water level

  • Details B. umbellatus is an herbaceous perennial to 1.2m, with upright, twisted grassy leaves and stiff stems bearing umbels of fragrant rosy-pink flowers 2cm in width in late summer

  • Plant range Eurasia


  • Foliage Deciduous

  • Habit Submerged

  • 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 Sun

  • Aspect South-facing or West-facing

  • Exposure Sheltered or Exposed


  • Chalk


  • Chalk


  • Chalk


  • MoisturePoorly-drained

  • SoilSand, Clay, Loam

  • pHNeutral, Acid, Alkaline


  • Ultimate height 1-1.5 metres

  • Ultimate spread 0.1-0.5 metres

  • Time to ultimate height 5-10 years

How to grow

Cultivation Grow in fertile mud at pond margins or in water up to 25cm deep, in full sun

Propagation Propagate by seed sown as soon as ripe or by rhizome division in spring

Suggested planting locations and garden types Cottage & Informal Garden Wildlife Gardens

How to care

Pruning Cut back after flowering

Pests Can get water lily aphid

Diseases Generally disease free

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