Iris sibirica 'Helen Astor' (Helen Astor Siberian Iris) — Clump-forming, upright

Overview

Iris sibirica 'Helen Astor' 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 and 0.3 m wide. Iris sibirica 'Helen Astor' 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. Suggested uses include borders, cut flowers and water gardens. It is native to Europe and Central Asia.

About

Iris sibirica 'Helen Astor' is a clump-forming, upright Siberian iris that flowers from May to July. It reaches about 0.6 m high with a 0.3 m spread and carries sword-shaped, often glaucous leaves. It prefers full sun but will tolerate some partial shade and suits south- or west-facing sites. As a Siberian iris it benefits from moisture-retentive, neutral to slightly alkaline soils such as loam or chalk.

Wikipedia contributors, CC BY-SA 4.0 — Iris sibirica

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

A clump-forming perennial in the iris family, Iris sibirica 'Helen Astor' traces its origins to the species native across Europe and Central Asia. The cultivar keeps the species habit of upright stems and grassy, sword-shaped leaves that are often glaucous. Flowering takes place from May to July, providing a focused period of bloom in late spring and early summer. Place plants in full sun for the best flowering, though a little light afternoon shade is tolerated. Soil should be neutral to slightly alkaline; typical media include loam or chalk and even sand where organic content retains moisture. As a Siberian-type iris it prefers moisture-retentive conditions rather than extremely free-draining beds. It is rated H5–H7 (hardy to fully hardy) in the UK and suits exposed or sheltered positions; listed USDA hardiness is 3–9. Plants mature to roughly 0.6 m tall with a 0.3 m spread, making them straightforward to place in mixed borders, water-margin schemes or for cutting. Try planting in groups to build presence in a south- or west-facing border, and use the May–July flowering window for picking stems at first-open bloom for the best vase life.

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 sibirica 'Helen Astor' 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
Spread: 0.3 m
Suggested uses: Borders, cut flowers, water gardens
Native to: Europe, Central Asia

Care notes

Pruning and caring for Iris sibirica 'Helen Astor'

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 sibirica 'Helen Astor'?

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 sibirica 'Helen Astor'?

Iris sibirica 'Helen Astor' prefers full sun; some tolerate partial shade. It suits exposed or sheltered positions.

What soil does Iris sibirica 'Helen Astor' need?

Iris sibirica 'Helen Astor' 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 sibirica 'Helen Astor'?

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 sibirica 'Helen Astor' grow?

Iris sibirica 'Helen Astor' reaches a height of 0.6 m and a spread of 0.3 m.

Is Iris sibirica 'Helen Astor' hardy in the UK?

Iris sibirica 'Helen Astor' 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 sibirica 'Helen Astor'?

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.

More in the Iris genus

Browse all Iris →