Iris trojana (Troy) — Clump-forming, upright

Overview

Iris trojana 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 trojana 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 Northwestern Turkey.

About

Iris trojana is a clump-forming, upright perennial from northwestern Turkey that produces flowers from May to July. Leaves are sword-shaped to grassy and often glaucous, with plants either deciduous or evergreen. It suits full sun but will tolerate some partial shade. Plant in well-drained neutral to slightly alkaline loam, chalk or sandy soils on a south- or west-facing site.

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 native of northwestern Turkey, Iris trojana forms upright clumps of sword-like leaves and puts on its flowering display from May to July. The foliage is often glaucous, ranging from grassy to more clearly sword-shaped, and individual plants may be either deciduous or retain their leaves through milder winters. Expect a late-spring to early-summer bloom period in a UK garden. Give Iris trojana a sunny, south- or west-facing position in neutral to slightly alkaline soil. It prefers well-drained loam, chalk or sandy soils and suits sites that are exposed or sheltered; some plants will tolerate a degree of partial shade but best flowering follows a sunny summer. In British hardiness terms it ranges H5–H7 (hardy to fully hardy) and corresponds to USDA zones 3–9, so it will withstand typical UK winters in open beds and borders. Use this iris where drainage is secure: gravel or sandy beds, dry banks and sunny border fronts suit its requirements. Plant where the foliage can be seen year-round if the selection is evergreen, and expect its main flowering season 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 trojana size, habit and characteristics

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

Care notes

Pruning and caring for Iris trojana

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 trojana?

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 trojana?

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

What soil does Iris trojana need?

Iris trojana 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 trojana?

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 trojana hardy in the UK?

Iris trojana 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 trojana?

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 →