Iris sibirica 'Cambridge' (Siberian Iris 'Cambridge') — Clump-forming, upright

Overview

Iris sibirica 'Cambridge' 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 and 0.3 m wide. Iris sibirica 'Cambridge' 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. Suggested uses include borders, cut flowers and water margins. It is native to Europe and Central Asia.

About

Iris sibirica 'Cambridge' is a clump-forming, upright perennial in the iris family, noted for its narrow, sword-shaped leaves and summer flowering. Plants reach about 0.6 m high with a 0.3 m spread and produce flowering stems from May to July. Leaves are often glaucous, giving a blue‑green cast through the season. It suits situations that favour moisture-retentive soil and a sunny, south- or west-facing position.

Wikipedia contributors, CC BY-SA 4.0 — Iris sibirica

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 member of the Iridaceae native to Europe and Central Asia, Iris sibirica 'Cambridge' grows as a clump-forming perennial with erect foliage and flowering stems. Expect plants to reach around 0.6 m tall with a compact 0.3 m spread; flowering occurs from May to July. The leaves are sword-shaped and often glaucous, providing an architectural, grass-like base for the flowering stems. Give the plant a sunny site, though it will tolerate some dappled shade; a south or west aspect is ideal. Soil should be neutral to slightly alkaline. While many irises favour free-draining loam, chalk or sand, Siberian types perform best in soils that retain some moisture yet do not sit waterlogged; the balance of moisture-retentive but well-drained conditions suits the rhizomatous root system. Plant with enough room for the clump to expand and allow air movement around the foliage; exposure may be exposed or sheltered. Hardiness ranges H5–H7 in the UK (USDA 3–9), so plants are hardy in most gardens. Use Iris sibirica 'Cambridge' in herbaceous borders, at water margins where soil stays reliably moist, or for cutting — stems make straightforward vase flowers. Flowers appear between May and July, providing a seasonal display above the narrow leaves.

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 sibirica 'Cambridge' 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
Spread: 0.3 m
Suggested uses: Borders, cut flowers, water margins
Native to: Europe, Central Asia

Care notes

Pruning and caring for Iris sibirica 'Cambridge'

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 sibirica 'Cambridge'?

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 sibirica 'Cambridge'?

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

What soil does Iris sibirica 'Cambridge' need?

Iris sibirica 'Cambridge' 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 sibirica 'Cambridge'?

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 sibirica 'Cambridge' grow?

Iris sibirica 'Cambridge' reaches a height of 0.6 m and a spread of 0.3 m.

Is Iris sibirica 'Cambridge' hardy in the UK?

Iris sibirica 'Cambridge' 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 sibirica 'Cambridge'?

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

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