Introduction

Blue flag iris has wonderfully textured, light-green foliage emerging directly from the ground in dense clumps (Figure 1). It grows 12 to 18 inches tall, producing lavender-blue flowers about 4 inches across in the spring. Flowers are displayed in a showy fashion slightly above the foliage. They are native to boggy areas where water stands all year long. They will grow in standing water.

General Information

Scientific name: Iris virginica

Pronunciation: EYE-riss vur-JIN-nick-uh

Common name(s): blue flag, blue flag iris

Family: Iridaceae

Plant type: herbaceous; ornamental grass; aquatic plant

USDA hardiness zones: 8B through 11 (Figure 2)

Planting month for zone 8: year round

Planting month for zone 9: year round

Planting month for zone 10 and 11: year round

Origin: native to Florida

Uses: border; mass planting; container or above-ground planter; naturalizing; water garden; accent

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

Description

Height: 4 to 7 feet

Spread: 1 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: evergreen

Leaf blade length: 18 to 36 inches

Leaf color: green

Fall color: no fall color change

Fall characteristic: not showy

Flower

Flower color: blue

Flower characteristic: spring flowering

Fruit

Fruit shape: elongated

Fruit length: .5 to 1 inch

Fruit cover: dry or hard

Fruit color: green

Fruit characteristic: persists on the plant

Trunk and Branches

Trunk/bark/branches: typically multi-trunked or clumping stems

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: extended flooding; slightly alkaline; clay; sand; acidic; loam

Drought tolerance: moderate

Soil salt tolerances: poor

Plant spacing: 24 to 36 inches

Other

Roots: not applicable

Winter interest: no special winter interest

Outstanding plant: not particularly outstanding

Invasive potential: aggressive, spreading plant

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. The plant flowers for a short period in the spring but the coarse-textured, upright foliage makes this a year-round favorite for a wet garden spot. It is well suited for planting in mass in front of a shrub border, or as a tall ground cover. On 2-foot centers, a thick ground cover can be formed in about 2 years. The individual plants will be nearly indistinguishable by that time.

Although full sun is tolerated if soils stay moist, a well-drained, partially shaded location provides the best habitat for Iris. Plants can be allowed to dry out slightly in a shaded location with little damage to foliage or flowers. As with other irises, over-fertilization 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.

Pests and Diseases

No major pest or diseases problems are usually encountered on this iris.