Iris ensata 'Rowden Knave'

RHS Plant Profile

Japanese water iris 'Rowden Knave'

Bogs Herbaceous Perennial

A clump-forming, rhizomatous deciduous perennial 60-90cm in height, with strap-like green leaves. Broad dark plum-purple flowers with darker veining, narrow white edges and tips and a yellow signal appear in the summer

Position

Full sun

Soil Types

Clay, Loam

Size

Time to Maturity: 2–5 years

Growing Conditions

Clay Loam

Moisture: Poorly–drained
pH: Acid or Neutral

Position

Full sun

Aspect: East–facing or South–facing or West–facing
Exposure: Exposed or Sheltered
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): H6

Colour & Scent

Season	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family: Iridaceae
Native to GB/Ireland: No
Foliage: Deciduous
Habit: Clump forming
Potentially harmful: Harmful if eaten. Wear gloves and other protective equipment when handling. Pets: Harmful if eaten. For further information and contact numbers regarding pets, see the HTA guide to potentially harmful plants
Genus: Iris may be rhizomatous or bulbous perennials, with narrow 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
Name Status: Accepted

How to Grow

Cultivation

Grow in moist to wet, deep, humus-rich, neutral to acid soil in sun or part shade; it thrives at the margins of ponds or streams

Propagation

Propagate by dividing iris rhizomes from midsummer to early autumn

Suggested planting locations and garden types

City and courtyard gardens
Cottage and informal garden
Flower borders and beds

Pruning

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

Pests

May be susceptible to slugs and snails

Diseases

May be susceptible to aphid-borne viruses, bacterial soft rot and grey moulds; see Iris diseases