Introduction

Japanese roof iris has wonderfully textured, light-green foliage emerging directly from the ground in dense clumps. It is closely related to the native crested iris. It grows 12 to 18 inches tall, producing blue flowers in the spring. Flowers are displayed in a showy fashion within the clump of foliage.

General Information

Scientific name: Iris tectorum

Pronunciation: EYE-riss teck-TOR-um

Common name(s): Japanese roof iris, wall iris

Family: Iridaceae

Plant type: herbaceous; ground cover

USDA hardiness zones: 6 through 10 (Figure 3)

Planting month for zone 7: year-round

Planting month for zone 8: year-round

Planting month for zone 9: year-round

Planting month for zone 10: year-round

Origin: not native to North America

Invasive potential: not known to be invasive

Uses: border; mass planting; ground cover; edging

Availability: somewhat available, may have to go out of the region to find the plant

Description

Height: 1 to 1.5 feet

Spread: 2 to 3 feet

Plant habit: upright

Plant density: moderate

Growth rate: moderate

Texture: coarse

Foliage

Leaf arrangement: most emerge from the soil, usually without a stem

Leaf type: simple

Leaf margin: entire

Leaf shape: linear

Leaf venation: parallel

Leaf type and persistence: semi-evergreen; evergreen

Leaf blade length: 12 to 18 inches

Leaf color: green

Fall color: no fall color change

Fall characteristic: not showy

Flower

Flower color: white

Flower characteristic: spring flowering

Fruit

Fruit shape: unknown

Fruit length: unknown

Fruit cover: unknown

Fruit color: unknown

Fruit characteristic: inconspicuous and not showy

Trunk and Branches

Trunk/bark/branches: not applicable

Current year stem/twig color: not applicable

Current year stem/twig thickness: not applicable

Culture

Light requirement: plant grows in part shade/part sun

Soil tolerances: acidic; sand; loam; clay

Drought tolerance: high

Soil salt tolerances: unknown

Plant spacing: 24 to 36 inches

Other

Roots: not applicable

Winter interest: no special winter interest

Outstanding plant: plant has outstanding ornamental features and could be planted more

Pest resistance: long-term health usually not affected by pests

Use and Management

The plant is grown and used for its foliage effect as well as the flower display. Many people may not notice the flowers nestled within the foliage clumps, but it is hard to miss the coarse-textured foliage. It is well suited for planting in mass in front of a shrub border, or as a ground cover. On 2-foot centers, a thick ground cover can be formed in about 2 years.

Although full sun is tolerated if soils stay moist, a well-drained, partially shaded location provides the best habitat for Japanese roof iris. Plants can be allowed to dry out in a shaded location with little damage to foliage or flowers. As with other irises, overfertilization will encourage foliage growth at the expense of flowers. A light application once each year should be enough to maintain good growth and a reliable flower display.