Iris kernerana — Clump-forming, upright

Overview

Iris kernerana 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 kernerana 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.

About

Iris kernerana is an upright, clump-forming perennial in the iris family, notable for its sword-shaped to grassy leaves which are often glaucous. The foliage can be deciduous or evergreen depending on type and season. It flowers in the UK from May to July. Plants suit a sunny, south- or west-facing position with well-drained soil.

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 kernerana belongs to the genus Iris (family Iridaceae) and forms upright clumps with sword-shaped to grassy leaves that are often glaucous; foliage may be deciduous or evergreen. Flowering runs from May to July, providing a mid-to-high season display before the foliage takes over for the remainder of the year. Give this iris full sun where possible; some tolerate a little light shade but the strongest flowering comes in a south- or west-facing spot. Soil can be loam, chalk or sand and should be neutral to slightly alkaline. Bearded types require sharply drained ground, while Siberian and Japanese kinds need a more moisture-retentive mix. Exposure can be either exposed or sheltered. Hardiness H5–H7 means it is winter-hardy across most of the UK (USDA zones 3–9). Place Iris kernerana in a sunny herbaceous border or any well-drained bed where its upright habit and glaucous leaves will show to advantage. Sit bearded forms on a raised ridge or freely draining mix; allow wetter, finer soil for moisture-loving Siberian or Japanese relatives. Expect blooms from May to July, and cut back spent flower stems to highlight the sword-shaped foliage after flowering.

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 kernerana size, habit and characteristics

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

Care notes

Pruning and caring for Iris kernerana

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 kernerana?

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 kernerana?

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

What soil does Iris kernerana need?

Iris kernerana 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 kernerana?

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 kernerana hardy in the UK?

Iris kernerana 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 kernerana?

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 →