Iris korolkowi — Clump-forming, upright

Overview

Iris korolkowi 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 korolkowi 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 Central Asia.

About

Iris korolkowi is a clump-forming, upright perennial iris from Central Asia, with sword-shaped to grassy leaves that are often glaucous. It flowers from May to July. It prefers full sun (though some plants tolerate partial shade) and favours neutral to slightly alkaline soils that drain freely. It suits south- or west-facing positions and will tolerate both exposed and sheltered sites in UK gardens.

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

A Central Asian species, Iris korolkowi forms upright clumps of sword-shaped to grassy leaves, often with a glaucous bloom on the foliage. Flowering occurs in the UK from May to July, so it provides early-summer interest on the flower stems while the leaves remain prominent afterwards. Plant where it receives full sun; some plants will tolerate a little light shade but best performance comes in a south- or west-facing spot. It does well in loam, chalk or sandy soils, and the genus has a general preference for neutral to slightly alkaline conditions. Good drainage is important for many iris types—bearded kinds in particular prefer sharply drained soil—while Siberian and Japanese irises require more moisture-retentive ground, so position choice should reflect the iris type you are growing. Hardiness for Iris korolkowi ranges H5–H7, meaning it is broadly hardy through most UK winters (H5 hardy to H7 fully hardy) and corresponds to USDA zones 3–9. Use it where upright, clump-forming perennials are wanted in sunny borders or planted singly on sunny banks; note the foliage colour when planning contrasts and expect flowering from May to July.

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 korolkowi size, habit and characteristics

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

Care notes

Pruning and caring for Iris korolkowi

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 korolkowi?

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 korolkowi?

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

What soil does Iris korolkowi need?

Iris korolkowi 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 korolkowi?

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 korolkowi hardy in the UK?

Iris korolkowi 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 korolkowi?

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 →