Iris innominata (Del Norte County iris) — Clump-forming, upright

Overview

Iris innominata 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 innominata 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 W USA.

About

Iris innominata is a clump-forming, upright perennial in the Iridaceae native to the western USA. It bears sword-shaped to grassy leaves that are often glaucous in tone and may be deciduous or evergreen. Plants flower in the UK from May to July. Wear gloves and other protective equipment when handling, as the plant is harmful if eaten.

Wikipedia contributors, CC BY-SA 4.0 — Iris innominata

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 innominata is a clump-forming perennial iris from the western USA, valued for its upright habit and sword-shaped, often glaucous leaves. As a member of the Iridaceae it suits planting where individual clumps can be shown to best effect rather than deep shade. Flowering takes place from May to July in the UK. Position it in full sun where possible; some examples tolerate a little afternoon shade. Soil should be neutral to slightly alkaline — loam, chalk or sand are all suitable where drainage is good. The general requirement is for well-drained conditions; note that some iris groups prefer sharply drained sites. For aspect choose a south- or west-facing spot and sites may be either exposed or sheltered, according to local conditions. Hardiness is H5–H7 (USDA 3–9), meaning plants are hardy outdoors through ordinary UK winters where those ratings apply. Use clumps in a sunny gravel or well-drained mixed border with room for air movement around the leaves. Take care when handling: the species is harmful if eaten, so wear gloves and other protective equipment and consult the HTA guide to potentially harmful plants for pet safety and contact numbers. Flowers appear in early to mid summer, so expect blooms between May and 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 innominata size, habit and characteristics

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

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 innominata?

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 innominata?

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

What soil does Iris innominata need?

Iris innominata 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 innominata?

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 innominata hardy in the UK?

Iris innominata 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 innominata?

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 innominata 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 →