Iris Oncocyclus Group — Clump-forming, upright

Overview

Iris Oncocyclus Group 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 Oncocyclus Group 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 Oncocyclus Group is a clump-forming, upright perennial in the iris family that flowers from May to July. Leaves are sword-shaped to grassy and often glaucous, and may be deciduous or evergreen. It performs best in full sun on a south- or west-facing site and prefers neutral to slightly alkaline, sharply drained soils for bearded kinds. Some species within the wider group, such as Siberian and Japanese types, need more moisture-retentive 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 Oncocyclus Group belongs to the Iridaceae and grows as an upright, clump-forming perennial with sword-like leaves that can carry a glaucous (blue-grey) bloom. Flowering runs from May to July. Plants tolerate exposed or sheltered positions and suit full sun, though a little partial shade is accepted by some forms. Soil preference is specific: choose loam, chalk or sand with neutral to slightly alkaline reaction and good drainage. Bearded types require especially sharp drainage to avoid rot, while Siberian and Japanese kinds within the wider grouping take more moisture-retentive soil. Position on a south- or west-facing slope or border helps ensure the best flowering display. Hardiness ranges H5–H7, meaning these irises are hardy across most of the UK from generally hardy to fully hardy; they also cover USDA zones 3–9. Use them where sharply drained, alkaline to neutral soils are available: gravelly or chalky borders, lean herbaceous edges and sunny beds where the foliage can remain dry between waterings. Expect the flowering season to be concentrated in mid to early summer, with blooms appearing above the glaucous foliage 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 Oncocyclus Group 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 Oncocyclus Group

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 Oncocyclus Group?

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 Oncocyclus Group?

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

What soil does Iris Oncocyclus Group need?

Iris Oncocyclus Group 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 Oncocyclus Group?

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 Oncocyclus Group hardy in the UK?

Iris Oncocyclus Group 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 Oncocyclus Group?

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 →