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Iris pseudacorus

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© RHS 1983

Characteristics

Plant type

Bog or Herbaceous Perennial

Habit

Suckering

Toxicity

Ingestion may cause severe discomfort

Resilience

Hardiness

old H4 (hardy)

Colour

Flower

Yellow in Summer

Foliage

Green in Spring and Summer

Size

Ultimate height

1-1.5 metres

Ultimate spread

1-1.5 metres

Time to ultimate height

2-5 years


Preferred common name

yellow flag

Family

Iridaceae


Iris may be rhizomatous or bulbous perennials, with narrowly leaves and erect stems bearing flowers with 3 large spreading or pendent fall petals, alternating with 3 erect, often smaller, standard petals, in late winter, spring or early summer

I. pseudacorus is a vigorous herbaceous perennial forming extensive colonies to 1.5m in height, with bright yellow flowers up to 10cm in width, the falls with brown veining in the centre, in mid and late summer

Other common names

  • daggers
  • flagon
  • Jacob's sword
  • water flag
  • water skegs
  • yellow fleur-de-lis

How to grow

Sunlight

  • Full sun
  • Part shade

Aspect

  • South-facing or East-facing
  • Exposed or Sheltered

Cultivation

Grow in wet, deep, acid, humus-rich soil in full sun or partial shade. It thrives at the margins of large ponds or streams; vigorous so site with care

Soil

  • Poorly-drained
  • Acid
  • Clay or Loam

Propagation

Propagate by division from midsummer to early autumn, plant immediately in flowering positions

Suggested planting locations and garden types

City/Courtyard Gardens, Coastal, Cottage/Informal Garden, Flower borders and beds or Wall-side Borders


How to care

Pruning

Remove any dying foliage in autumn, old flower stems can be cut down after flowering

Pests

May be attacked by slugs, snails and thrips

Diseases

Susceptible to aphid borne viruses, bacterial soft rot and Botrytis