Iris forrestii (Forrest iris) — Clump-forming, upright

Overview

Iris forrestii 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 forrestii 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 SW China.

About

Iris forrestii is a clump-forming, upright perennial iris from southwest China that flowers in the UK from May to July. It carries sword-shaped to grassy leaves that are often glaucous, and plants form compact clumps. Best placed in full sun, it will tolerate some light shade. Handle with care as the species is harmful if eaten and protective gloves are recommended when handling.

Wikipedia contributors, CC BY-SA 4.0 — Iris forrestii

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 forrestii is a perennial in the Iridaceae, native to southwest China, valued for its compact, clump-forming habit and upright stems. In the UK it flowers from May to July. The foliage is sword-shaped to grassy and often has a glaucous bloom, which gives clumps a distinctive tone through the growing season. Plant in a sunny south- or west-facing spot, though it will tolerate some light afternoon shade. It prefers loam, chalk or sandy soils that are well drained and a neutral to slightly alkaline pH. Exposure can be either sheltered or open; the plant’s hardiness rating (H5–H7) means it is hardy through typical UK winters, from generally hardy to fully hardy in the coldest districts. For readers outside the UK, USDA zones 3–9 indicate a similarly wide climatic tolerance. Keep soil free-draining but avoid placing rhizomes where water pools. Wear gloves and other protective equipment when dividing or handling plants, since Iris forrestii is harmful if eaten and can irritate skin. Expect upright clumps to produce their seasonal blooms between May and July, sitting above the foliage.

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 forrestii size, habit and characteristics

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

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 forrestii?

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 forrestii?

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

What soil does Iris forrestii need?

Iris forrestii 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 forrestii?

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 forrestii hardy in the UK?

Iris forrestii 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 forrestii?

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 forrestii 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 →