Iris ensata of gardens (Japanese water iris) — Clump-forming, upright

Overview

Iris ensata of gardens is a clump-forming, upright perennial in the genus Iris, part of the Iridaceae family, with deciduous or evergreen; sword-shaped to grassy, often glaucous foliage. It typically grows around 0.6 m tall. Iris ensata of gardens grows best in full sun; some tolerate partial shade, and tolerates loam and chalk or sand; sharply drained for bearded kinds soils and neutral to slightly alkaline pH. Its UK hardiness is rated H5–H7. It is native to E Asia.

About

Iris ensata of gardens is a clump-forming, upright perennial iris that flowers May to July. It grows to about 0.6 m with sword-shaped to grassy foliage that is often glaucous. Give it full sun or light afternoon shade on a south- or west-facing site, and a moisture-retentive soil rather than a sharply drained one. Wear gloves when handling: the plant is harmful if eaten.

Wikipedia contributors, CC BY-SA 4.0 — Iris ensata

About the genus

Iris takes its name from the Greek goddess of the rainbow, and for once the naming feels entirely earned. I can't think of another genus that covers so much ground — inky purples, burnt apricots, clean whites, blues that seem lit from inside — or so many situations. There are bearded irises that want their rhizomes baked in full sun, Siberian types happy in ordinary border soil, and species that will sit contentedly at the edge of a pond. What they share is the flower: three petals standing up, three falling away, built with a kind of architectural confidence most plants never attempt. Even out of bloom the foliage earns its place — those upright fans of blue-green leaves hold a border together for months. I grow them for the fortnight in May and June when nothing else in the garden can compete, and I've made my peace with that. Some plants are for the long haul. An iris is an event.

Written by Henry

In the garden

Iris ensata of gardens is a clump-forming perennial native to east Asia, grown for its seasonal display from May to July. It reaches roughly 0.6 m and carries sword-shaped to grassy leaves that are often glaucous in tone. The species suits planting where soil can hold moisture rather than running off quickly. Plant in full sun, allowing for some partial shade if afternoon heat is an issue, on a south- or west-facing aspect for best flowering. Soil pH should be neutral to slightly alkaline; typical soil types include loam, chalk or sand, but Japanese kinds do best in moisture-retentive loam rather than sharply drained sites. Exposure may be either sheltered or fairly exposed, and the plant is winter-hardy across H5–H7 (hardy to fully hardy) in the UK. Use Iris ensata of gardens at pond margins, in damp perennial beds or alongside moisture-retentive borders where its upright clumps can be seen at eye level. Avoid placing it where the root zone dries out completely between rains. Handle with care and wear gloves, since the plant is harmful if eaten and can irritate skin.

Growing conditions

Best soil and position for Iris

Sunlight: Full sun; some tolerate partial shade
Soil type: Loam, chalk or sand; sharply drained for bearded kinds
Soil pH: Neutral to slightly alkaline
Soil moisture: Well drained; Siberian and Japanese kinds need moisture-retentive soil
Aspect: South or west facing
Exposure: Exposed or sheltered
UK hardiness: H5–H7

Plant details

Iris ensata of gardens size, habit and characteristics

Plant type: Perennial
Habit: Clump-forming, upright
Foliage: Deciduous or evergreen; sword-shaped to grassy, often glaucous
Height: 0.6 m
Native to: E Asia
Toxicity: 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

Care notes

Pruning and caring for Iris ensata of gardens

Cultivation: Plant bearded irises with the top of the rhizome exposed so it can bake in summer sun; beardless kinds sit just below the surface in richer, damper ground. Feed with a low-nitrogen fertiliser after flowering and keep the rhizomes clear of mulch and encroaching neighbours.
Pruning: Remove spent flower stems at the base. Trim the outer leaves back by about half in late autumn to reduce overwintering fungal spores, leaving the central fan intact.
Propagation: Divide rhizomes six to eight weeks after flowering, discarding the old woody centre and replanting vigorous outer sections. Species come from seed, but named cultivars will not come true.
Pest resistance: Generally trouble-free, though iris sawfly and slugs damage foliage and thrips can disfigure buds.
Disease resistance: Prone to leaf spot, and to rhizome rot wherever drainage is poor or planting too deep.

Frequently asked questions

How do I grow Iris ensata of gardens?

Plant bearded irises with the top of the rhizome exposed so it can bake in summer sun; beardless kinds sit just below the surface in richer, damper ground. Feed with a low-nitrogen fertiliser after flowering and keep the rhizomes clear of mulch and encroaching neighbours.

Where is the best place to plant Iris ensata of gardens?

Iris ensata of gardens prefers full sun; some tolerate partial shade. It suits exposed or sheltered positions.

What soil does Iris ensata of gardens need?

Iris ensata of gardens grows best in loam and chalk or sand; sharply drained for bearded kinds soil. It prefers neutral to slightly alkaline soil. Aim for soil that stays well drained; siberian and japanese kinds need moisture-retentive soil.

How do I prune Iris ensata of gardens?

Remove spent flower stems at the base. Trim the outer leaves back by about half in late autumn to reduce overwintering fungal spores, leaving the central fan intact.

How big does Iris ensata of gardens grow?

Iris ensata of gardens reaches a height of 0.6 m.

Is Iris ensata of gardens hardy in the UK?

Iris ensata of gardens has an RHS hardiness rating of H5, meaning it is hardy in most of the UK, tolerating -15 to -10°C.

How do I propagate Iris ensata of gardens?

Divide rhizomes six to eight weeks after flowering, discarding the old woody centre and replanting vigorous outer sections. Species come from seed, but named cultivars will not come true.

Is Iris ensata of gardens toxic?

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.

More in the Iris genus

Browse all Iris →