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Iris virginica Blue Flag, Blue Flag Iris1

Edward F. Gilman 2

Introduction

Blue flag iris has wonderfully textured, light-green foliage emerging directly from the ground in dense clumps (Fig. 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.

Figure 1. Blue flag iris
Figure 1.  Blue flag iris

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 (Fig. 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

Figure 2. Shaded area represents potential planting range.
Figure 2.  Shaded area represents potential planting range.

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

Figure 3. Flower of blue flag.
Figure 3.  Flower of blue flag.

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.

Footnotes

1. This document is FPS-288, one of a series of the Environmental Horticulture Department, UF/IFAS Extension. Original publication date October 1999. Reviewed February 2014. Visit the EDIS website at https://edis.ifas.ufl.edu.
2. Edward F. Gilman, professor, Environmental Horticulture Department; UF/IFAS Extension, Gainesville, FL 32611.

Publication #FPS-288

Date: 8/10/2015

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      Contacts

      • Gail Hansen de Chapman