Iris ensata 'Alba'

RHS Plant Profile

Japanese water iris 'Alba'

Herbaceous Perennial

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A clump-forming, upright perennial, to around 90cm high in flower, with narrowly sword-shaped, slightly grey-green leaves. Flowers have short, ruffled, creamy white standards, and broad white falls with a streak of gold at the base

Position

Full sun, Partial shade

Soil Types

Clay, Loam

Max Height

0.5-1 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity: 2–5 years
Max Spread: 0.1-0.5 metres
Max Height: 0.5-1 metres

Growing Conditions

Clay Loam

Moisture: Moist but well–drained or Poorly–drained
pH: Acid or Neutral

Position

Full sun Partial shade

Aspect: East–facing or South–facing or West–facing
Exposure: 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: Unresolved

How to Grow

Cultivation

Thrives in moist, humus rich, ideally neutral to slightly acid soil. Will tolerate part shade but flowering is best in full sun. Suitable for planting at the edges of ponds and streams, or in a border where the soil does not dry out

Propagation

Propagate by division, see dividing irises for more detailed advice

Suggested planting locations and garden types

Cottage and informal garden
Flower borders and beds

Pruning

Remove spent flower stems after flowering, and any dying foliage in autumn

Pests

May be susceptible to aphids, slugs, snails, thrips and iris sawfly

Diseases

May be susceptible to aphid-borne virus diseases and grey moulds; see Iris diseases