Siberian iris

Sun

Full sun to partial shade; afternoon shade helps in hotter areas. Too much shade reduces flowering.

Water

Keep the soil consistently moist during establishment and spring growth. Established clumps tolerate brief dry spells, but prolonged drought reduces flowering and damages foliage.

Soil

Fertile, moisture-retentive soil with good drainage; slightly acidic to neutral soil is ideal. Tolerates clay, but is not a plant for permanent standing water.

Height

2-4 ft (0.6-1.2 m)

Spread

1.5-2.5 ft (0.45-0.75 m)

Flowers

Late spring to early summer; blue-violet flowers with pale, finely veined markings at the base of the drooping outer petals. White-flowered forms also occur.

Foliage

Narrow, upright to arching green leaves form dense, grassy clumps; leaves turn yellow or brown in autumn.

Growth

Moderate; young divisions may take two or three years to form substantial flowering clumps.

Care needed

Low

• Plant with the rhizomes just below the soil surface, unlike bearded irises, whose rhizomes are left exposed.
• Water deeply during dry spring and early-summer weather, especially while plants establish.
• Apply compost in spring; use a light application of balanced fertiliser only if growth is weak.
• Mulch around the clump to conserve moisture, keeping mulch away from the crown.
• Divide congested clumps when flowering declines or the centre becomes bare, usually every three to five years.

Pruning. Cut spent flower stems to the base after flowering unless you want seed. Leave green leaves intact, then remove dead foliage in late autumn or before new growth begins in early spring.

Early spring

Remove remaining dead leaves before new shoots lengthen.

Spring

Plant or divide clumps, water thoroughly and renew the mulch.

Late spring

Keep the root zone moist while flower buds develop.

Early summer

Cut off finished flower stems unless saving seed.

Summer

Water during prolonged dry spells; do not cut back healthy foliage.

Late autumn

Remove collapsed foliage and dispose of any leaves showing disease.

• Plant repeated clumps through a mixed border to give vertical rhythm among rounded perennials.
• Use beside a pond or rain garden, above the permanently flooded zone.
• Combine with peonies and hardy geraniums for a late-spring cottage border.
• Plant in broad groups with ornamental grasses for a meadow-like effect that retains structure after flowering.

Garden styles it suits: English country, Cottage garden, New perennial (prairie), Blues and silvers, Bog garden and Japanese.

Plant it with: Peonies, Hardy geraniums, Siberian bugloss, Astilbes, Lady's mantle and Tufted hair grass.

Wildlife: Flowers are visited by bees. Deer and rabbits often leave established plants alone, but browsing resistance is not guaranteed.

• Poor flowering: improve sunlight, water during spring growth and divide crowded clumps; avoid excessive nitrogen feeding.
• Iris borer, chiefly in eastern North America: remove old foliage before spring growth and remove affected stems or rhizomes promptly.
• Leaf spot: remove badly affected foliage, clear dead leaves and water the soil rather than the leaves.
• Rhizome or crown rot in stagnant, waterlogged soil: improve drainage, remove rotten tissue and replant healthy divisions in a better-drained position.

Treat all parts as toxic to cats, dogs, horses and people if eaten, especially the rhizomes. Ingestion can cause drooling, nausea, vomiting, abdominal pain and diarrhoea; serious poisoning is uncommon, but seek medical or veterinary advice after ingestion. Sap may irritate skin, so wear gloves when dividing.

• Japanese iris (Iris ensata)

  Usually flowers later, with much larger, flatter flowers and broader leaves with a prominent raised midrib.

• Bearded iris (Iris germanica)

  Has broader, sword-shaped leaves, thick surface rhizomes and a conspicuous fuzzy beard on each drooping outer petal; Siberian iris has no beard.

• Yellow flag iris (Iris pseudacorus)

  Has yellow flowers, much broader leaves and a heavier, more vigorous habit. It commonly grows in standing water and is invasive in many regions.

Iris is the Greek word for rainbow, while sibirica means 'of Siberia', giving rise to the common name Siberian iris.

Propagation. Divide in early spring or shortly after flowering, keeping roots moist and replanting promptly. Use substantial divisions with several fans of leaves. Seed can be sown outdoors in autumn, but seedlings take several years to flower and named cultivars do not come true from seed.

Accepted botanical name

Iris sibirica

In the US and Canada

Introduced in Canada and the lower 48 states.

Native range

Altay, Austria, Baltic States, Belarus, Bulgaria, Central European Rus, Czechoslovakia, East European Russia, France, Germany, Hungary and Italy.

Measured

Soil pH 7 to 7.5. Average height 65 cm.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.