Iris sibirica 'Heavenly Blue' (Siberian Iris 'Heavenly Blue') — Clump-forming, upright

Overview

Iris sibirica 'Heavenly Blue' 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 'Heavenly Blue' 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 margins. It is native to Europe and Central Asia.

About

Iris sibirica 'Heavenly Blue' is a clump-forming, upright perennial in the iris family with narrow, sword-shaped leaves that are often glaucous. It reaches about 0.6 m tall with a spread of roughly 0.3 m. Flowering occurs from May to July. Plant in a south- or west-facing spot in neutral to slightly alkaline soil.

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

Iris sibirica 'Heavenly Blue' belongs to the Iridaceae and originates from Europe and Central Asia. It grows from a rhizomatous clump, producing upright stems and grassy, sword-shaped leaves that frequently have a glaucous (blue-green) cast. Flowering in the UK runs from May to July. Choose a site in full sun where possible, although the species will tolerate some partial shade. Soil type can be loam, chalk or sand provided it suits the plant's preference for neutral to slightly alkaline pH; while many irises prefer sharply drained conditions, Siberian types perform best where the soil retains some moisture without waterlogging. Aspect on a south or west-facing border helps encourage flowering, and plants will tolerate both exposed and sheltered situations. Hardiness is rated H5–H7 (hardy to fully hardy) in the UK and USDA zones 3–9, so it withstands typical seasonal frosts. Allow individual clumps room (about 0.3 m) and use in mixed borders, as reliable cut flowers or planted at pond edges and water margins where the soil remains reliably moist. Expect flowering stems suitable for cutting 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 sibirica 'Heavenly Blue' 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 margins
Native to: Europe, Central Asia

Care notes

Pruning and caring for Iris sibirica 'Heavenly Blue'

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 'Heavenly Blue'?

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 'Heavenly Blue'?

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

What soil does Iris sibirica 'Heavenly Blue' need?

Iris sibirica 'Heavenly Blue' 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 'Heavenly Blue'?

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 'Heavenly Blue' grow?

Iris sibirica 'Heavenly Blue' reaches a height of 0.6 m and a spread of 0.3 m.

Is Iris sibirica 'Heavenly Blue' hardy in the UK?

Iris sibirica 'Heavenly Blue' 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 'Heavenly Blue'?

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 →