Blue Flag Iris

Beginning to bloom in my garden as I write this, is one of my favourites – Iris versicolor or blue flag iris. Its glorious royal purple blossoms are a real eye catcher. If you have sufficient moisture, it can be a garden show stopper in June before the bulk of the colourful summer and fall natives have started to bloom. (Plant Description and In the Garden sections, below, courtesy of Shaun Booth from In Our Nature.) 

Common Name: Blue Flag Iris 

Scientific Name: Iris versicolor 

Family: Iridaceae (Iris Family) 

Alternate Common Names: American Blue Flag, Dagger Flower, Flag Lily, Harlequin Blueflag, Large Blue Iris, Larger Blue Flag, Multi-coloured Blue Flag, Northern Blue Flag, Northern Iris, Poison Flag, Snake Lily, Water Flag 

Plant description: Blue Flag Iris features sword-like basal leaves that are usually erect but larger leaves may be slightly spreading. They are about 2.5cm wide at the base, taper gradually to a pointed tip and are often purple at the base. Smooth flowering stalks emerge from the base of the plant and are topped by 1 to a few flowers that each measure up to 10cm across. These flowers are a very familiar Iris shape with 3 sepals, 3 petals and 3 stamens. The sepals spread outwards from the center of the flower and each one has a patch of yellow and white at the base with purple veins fanning out from it. The upper lip of this sepal curves up like a shoehorn and forms an open tubular shape with the bottom lip. The petals are found in between the sepals, measure 2/3 the length of the sepals and are violet-blue with dark purple veins. Flowers are replaced by angular, oblong seed capsules that split open to release its seeds. 

In the Garden: Blue Flag Iris steals the show in early summer with its intricate, jewel-toned flowers and its bold, sword-like leaves. The flowers are relished by hummingbirds but deer and other herbivores rarely touch this plant. In addition, the angular seed pods add excellent winter interest. 

Skill level: beginner 

Lifespan: perennial 

Exposure: full sun to part shade 

Soil Type: prefers clay and mucky soils but will grow in most soils (I have seen them growing in the shoulder gravel of a road) 

Moisture: wet, moist – will tolerate short periods of drought 

Height: 60-90 cm 

Spread:  60-75 cm 

Bloom Period: May, Jun, Jul 

Colour: blue/purple 

Fragrant (Y/N):

Showy Fruit (Y/N):  N   

Cut Flower (Y/N):

Pests: susceptible to a number of insect pests including iris borer, iris thrips, and aphids and potential disease problems include various rots (rhizome rot, crown rot, bacterial soft rot) leaf spot, and leaf/blossom blight while aphids can spread mosaic virus 

Natural Habitat: marshes, swamps, shorelines, wet meadows, margins of ponds and creeks, sedge meadows and borders of wetland forests 

Wildlife value: attracts butterflies and native bees. Hummingbirds seek nectar from the flowers. 

Butterfly Larva Host Plant For: none 

USDA Hardiness Zone: 2-7 

Propagation: [C(120), M; D] Seeds should be sown when fresh or, if sowing later, stored in a cool, moist setting (most sources say they do not tolerate drying out – though Cullina claims they do just fine stored dry). They require at least 4 months cold, moist stratification to germinate and will take 2 years till they produce flowers. To propagate vegetatively, the roots can be divided in early summer and potted or planted along the water’s edge. 

Additional Info: In smaller water features, consider growing this in large pots submerged to the rim. 

Native Range:

Iris versicolor is a northern native, growing along streambanks, lakes and ponds, and in open wetlands.