Iris setosa (bristle-pointed iris) — Clump-forming, upright

Overview

Iris setosa 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. Iris setosa 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 N America and E Asia.

About

Iris setosa is a clump-forming, upright perennial in the iris family with violet-to-blue flowers and sword-shaped, often glaucous leaves. It grows to about 0.6 m and flowers from May to July. Plants suit full sun, though some will tolerate light afternoon shade, and prefer neutral to slightly alkaline, well-drained soils.

Wikipedia contributors, CC BY-SA 4.0 — Iris setosa

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 setosa originates from North America and East Asia and performs as a clump-forming perennial in temperate gardens. The plant carries sword-shaped foliage that is frequently glaucous and produces violet to blue or lavender blooms in late spring and early summer. In the UK it is reliably hardy (H5–H7), corresponding to garden conditions from 'hardy' through 'very' to 'fully hardy', and it also occupies USDA zones 3–9. Give Iris setosa a sunny position, ideally south- or west-facing, although it will tolerate some partial shade. Soil should be neutral to slightly alkaline — loam, chalk or sandy mixes suit it provided they drain freely. The species will tolerate exposed or sheltered sites, so choose a spot with good light and air movement to reduce rot in poor drains. Handle with care: all parts are harmful if eaten, and gloves or other protective equipment are recommended when working with the plant; for pet-related advice consult the HTA guide to potentially harmful plants. Expect clump-forming growth to provide neat perennial structure and violet-to-blue flowers 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 setosa 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
Native to: N America, E 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 setosa

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 setosa?

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 setosa?

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

What soil does Iris setosa need?

Iris setosa 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 setosa?

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 setosa grow?

Iris setosa reaches a height of 0.6 m.

Is Iris setosa hardy in the UK?

Iris setosa 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 setosa?

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 setosa 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 →