Iris kaempferi 'Gei-sho-Ui' (Japanese Iris) — Clump-forming, upright

Overview

Iris kaempferi 'Gei-sho-Ui' 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. Iris kaempferi 'Gei-sho-Ui' 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 Japan.

About

Iris kaempferi 'Gei-sho-Ui' is a clump-forming, upright perennial in the Iridaceae with sword-shaped, often glaucous leaves. It flowers from May to July. Best positioned in full sun, it will tolerate some light shade. Hardiness is H5–H7 across the UK.

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 kaempferi 'Gei-sho-Ui' belongs to the iris family and originates from Japan. It forms upright clumps of sword-like leaves that are often glaucous in tone, and produces its flowering display between May and July. The plant sits within the group commonly known as Japanese iris and shares their preference for a seasonally moist root run. Plant in full sun for the most abundant flowering, although a little afternoon shade is acceptable. Soils of loam, chalk or sand are all suitable provided the root zone remains appropriate for the iris type: Japanese and Siberian kinds benefit from a moisture-retentive substrate rather than the sharply drained conditions used for bearded irises. Aim for a neutral to slightly alkaline pH and choose a south- or west-facing location; the cultivar tolerates both exposed and sheltered sites. In UK gardens it suits moisture-retentive borders where its upright habit can be displayed. With an assessed hardiness of H5–H7 it is classed from hardy to fully hardy across much of Britain (USDA 3–9). Flowering in May to July gives a strong mid-season presence that is typical of Japanese iris cultivars.

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 kaempferi 'Gei-sho-Ui' size, habit and characteristics

Plant type: Perennial
Habit: Clump-forming, upright
Foliage: Deciduous or evergreen; sword-shaped to grassy, often glaucous
Native to: Japan

Care notes

Pruning and caring for Iris kaempferi 'Gei-sho-Ui'

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 kaempferi 'Gei-sho-Ui'?

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 kaempferi 'Gei-sho-Ui'?

Iris kaempferi 'Gei-sho-Ui' prefers full sun; some tolerate partial shade. It suits exposed or sheltered positions.

What soil does Iris kaempferi 'Gei-sho-Ui' need?

Iris kaempferi 'Gei-sho-Ui' 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 kaempferi 'Gei-sho-Ui'?

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.

Is Iris kaempferi 'Gei-sho-Ui' hardy in the UK?

Iris kaempferi 'Gei-sho-Ui' 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 kaempferi 'Gei-sho-Ui'?

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.

More in the Iris genus

Browse all Iris →