Iris spuria (blue iris) — Clump-forming, upright

Overview

Iris spuria 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 spuria 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 Europe and SW Asia.

About

Iris spuria is a clump-forming, upright perennial with sword-shaped to grassy leaves and a tendency to a glaucous leaf surface. It produces purple to lilac flowers that sit above the foliage in late spring to mid-summer. Suits well-drained soils on neutral to slightly alkaline sites and prefers a south- or west-facing position. Harmful if eaten; wear gloves and protective equipment when handling.

Wikipedia contributors, CC BY-SA 4.0 — Iris spuria

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 spuria (blue iris) is a clump-forming perennial native to Europe and south-west Asia, grown for its erect habit and narrow, sword-shaped leaves that are often glaucous. Flowering runs from May to July, when slender stems carry purple to lilac blooms above the foliage. The species is classed H5–H7, meaning it is hardy through most UK winters (H5 = hardy; H6 = very hardy; H7 = fully hardy) and will tolerate exposed sites as well as more sheltered corners. Give Iris spuria full sun where possible; some plants will tolerate light afternoon shade. It prefers loam, chalk or sandy soils that are neutral to slightly alkaline and generally needs good drainage — the exception being Siberian and Japanese types, which perform better in more moisture-retentive ground. A south- or west-facing aspect helps produce the best flowering display. When planting, set rhizomes so they sit at or just below the soil surface to reduce rot risk in heavy soils. Place it in mixed borders where upright habit provides structure, or use in drifts along a sunny bank or gravelly slope. Take care when handling: the plant is harmful if eaten and can irritate skin, and pet owners should consult the HTA guide to potentially harmful plants for contact numbers and further advice. Flowers appear well above the leaves from May to July, making their timing easy to plan in a seasonal scheme.

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 spuria size, habit and characteristics

Plant type: Perennial
Habit: Clump-forming, upright
Foliage: Deciduous or evergreen; sword-shaped to grassy, often glaucous
Native to: Europe, SW Asia
Toxicity: Harmful if eaten. Wear gloves and other protective equipment when handling. Pets: Harmful if eaten. For further information and contact numbers regarding pets, see the HTA guide to potentially harmful plants

Care notes

Pruning and caring for Iris spuria

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 spuria?

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 spuria?

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

What soil does Iris spuria need?

Iris spuria 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 spuria?

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 spuria hardy in the UK?

Iris spuria 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 spuria?

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.

Is Iris spuria toxic?

Harmful if eaten. Wear gloves and other protective equipment when handling. Pets: Harmful if eaten. For further information and contact numbers regarding pets, see the HTA guide to potentially harmful plants.

More in the Iris genus

Browse all Iris →