Iris chrysographes 'Black Knight' (iris 'Black Knight') — Clump-forming, upright

Overview

Iris chrysographes 'Black Knight' 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 chrysographes 'Black Knight' 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 Southern China and Myanmar.

About

Iris chrysographes 'Black Knight' is a clump-forming, upright perennial prized for its very dark violet, almost black flowers. Leaves are sword-shaped and often show a glaucous, greyish-green tone, dying back after flowering. It flowers in the UK from May to July and the blooms are lightly scented. Handle with care: all parts are harmful if eaten and gloves are recommended when planting or dividing.

Wikipedia contributors, CC BY-SA 4.0 — Iris chrysographes

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 chrysographes 'Black Knight' is a Sino‑Asian iris native to southern China and Myanmar, brought into gardens for its unusually dark blooms. It forms erect clumps of sword-shaped leaves that may appear glaucous and produces hollow flowering stems bearing lightly scented flowers in early summer. Plant it in full sun where possible, though it will tolerate some partial shade; a south- or west-facing spot suits it best. It prefers neutral to slightly alkaline soils — loam, chalk or sand — kept well drained, and is rated H5–H7 (hardy to fully hardy) across the UK. In USDA terms it corresponds to zones 3–9. While the species benefits from free-draining ground, give established clumps a summer position that avoids waterlogged conditions. Use Iris chrysographes 'Black Knight' where a low clump with strong, dark blooms is needed: front of a sunny border, edging a gravel path, or alongside late-spring bulbs. Wear gloves and other protective equipment when handling, as all parts are harmful if eaten; for pet-related information and contact numbers consult the HTA guide to potentially harmful plants. The outer falls of the flowers commonly carry a narrow golden-yellow central stripe, a useful identification detail at close range.

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 chrysographes 'Black Knight' size, habit and characteristics

Plant type: Perennial
Habit: Clump-forming, upright
Foliage: Deciduous or evergreen; sword-shaped to grassy, often glaucous
Native to: Southern China, Myanmar
Fragrance: Flower
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 chrysographes 'Black Knight'

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 chrysographes 'Black Knight'?

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 chrysographes 'Black Knight'?

Iris chrysographes 'Black Knight' prefers full sun; some tolerate partial shade. It suits exposed or sheltered positions.

What soil does Iris chrysographes 'Black Knight' need?

Iris chrysographes 'Black Knight' 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 chrysographes 'Black Knight'?

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 chrysographes 'Black Knight' hardy in the UK?

Iris chrysographes 'Black Knight' 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 chrysographes 'Black Knight'?

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 chrysographes 'Black Knight' 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 →