Iris douglasiana (Douglas iris) — Clump-forming, upright

Overview

Iris douglasiana 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 0.3 m tall. Iris douglasiana 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 North W America.

About

Iris douglasiana is a clump-forming, upright perennial with sword-shaped to grassy leaves and a compact habit reaching about 0.3 m. Its foliage can be deciduous or evergreen and is often glaucous; leaves may show a red tinge at the base. Flowers appear in the UK from May to July and are most often purplish-blue, with white or yellow forms recorded. The plant is hardy (H5–H7) but is harmful if eaten, so handle with gloves and care around pets.

Wikipedia contributors, CC BY-SA 4.0 — Iris douglasiana

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 douglasiana originates from North W America and is a member of the Iridaceae suited to temperate coastal and lowland conditions. It forms neat clumps of sword-shaped leaves and typically reaches about 0.3 m high; flowering in the UK runs from May to July when the stems bear usually purplish-blue blooms, sometimes white or yellow. Plant in full sun where possible, though many specimens will tolerate some light afternoon shade. A south or west aspect suits the species best. Soil should be neutral to slightly alkaline and freely draining; typical acceptable substrates include loam, chalk or sand. The species tolerates exposed as well as sheltered sites and falls within UK hardiness H5–H7 (USDA 3–9), so it survives most British winters without additional protection. Use Iris douglasiana in sunny borders, gravelly or well-drained coastal beds and grouped as small clumps at the front of mixed perennial beds. Keep planting positions clear of dense competitors so the clump can spread; after flowering in May to July, remove spent stems to keep the foliage tidy. Remember it is harmful if eaten and wear gloves when handling; for pet-safety contacts consult the HTA guide to potentially harmful plants.

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 douglasiana size, habit and characteristics

Plant type: Perennial
Habit: Clump-forming, upright
Foliage: Deciduous or evergreen; sword-shaped to grassy, often glaucous
Height: 0.3 m
Native to: North W America
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 douglasiana

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 douglasiana?

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 douglasiana?

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

What soil does Iris douglasiana need?

Iris douglasiana 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 douglasiana?

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 douglasiana grow?

Iris douglasiana reaches a height of 0.3 m.

Is Iris douglasiana hardy in the UK?

Iris douglasiana 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 douglasiana?

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 douglasiana 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 →