Iris stolonifera (stolon-spreading iris) — Clump-forming, upright

Overview

Iris stolonifera 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 stolonifera 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 C Asia.

About

Iris stolonifera is a clump-forming, upright perennial in the iris family with glaucous, sword-shaped leaves. It produces its flowers in the UK from May to July. The plant suits full sun but will tolerate some light shade and prefers neutral to slightly alkaline, sharply drained soils such as loam, chalk or sand. Wear gloves and other protective equipment when handling as it is harmful if eaten.

Wikipedia contributors, CC BY-SA 4.0 — Iris stolonifera

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 stolonifera comes from Central Asia and belongs to the Iridaceae family; it forms an upright clump with blue‑green, sword‑shaped leaves that may be deciduous or remain semi‑persistent depending on the season. Flowering occurs in the UK between May and July, after which the foliage may die back or persist into summer. Sit this iris in full sun for best flowering, although some tolerance of partial shade is recorded. It prefers neutral to slightly alkaline soils and will do well on loam, chalk or sandy substrates; for bearded types, sharp drainage is important. Choose a south- or west‑facing position where the soil is free‑draining and avoid persistently waterlogged ground. UK hardiness runs from H5 to H7 (roughly hardy to fully hardy), and it is also suitable across USDA zones 3–9. Use Iris stolonifera where an upright, architectural leaf will fit — a sunny border, a gravel or chalk bed, or a well‑drained position at the front of a mixed border. Keep in mind the plant is harmful if eaten, so wear gloves when planting or dividing and keep it away from areas where pets or children might sample foliage.

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 stolonifera size, habit and characteristics

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

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 stolonifera?

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 stolonifera?

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

What soil does Iris stolonifera need?

Iris stolonifera 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 stolonifera?

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 stolonifera hardy in the UK?

Iris stolonifera 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 stolonifera?

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 stolonifera 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 →