wetland wildflower

Western blue flag

Iris missouriensis

Also known as Rocky Mountain Iris

Native to the Pacific Coast, the Southwest, and the Rockies and southern Canada

British Columbia to southern California (mostly east of the Cascades), east to the Dakotas, New Mexico and Mexico

Light Full sun Sun tolerance
Moisture Wet Moisture preference
Zones 2–9 Cold to heat range
Bloom May–Jul Flowering time
Height up to 2 ft to 0.6 m
Life cycle Perennial Annual to perennial

Full details, see below

In the garden

A wetland wildflower for full sun and wet soil. Its purple flowers peak in June. At up to 2 ft, it suits rain gardens, pond edges, and damp low spots. It spreads readily, so give it room or a contained spot. Hardy in USDA zones 2–9.

Growing conditions

Light

Full sun Partial shade Full shade

Moisture

Dry Moist Wet

Hardiness zones

Find your zone:

When it blooms

The Western blue flag's purple flowers bloom May to July, peaking in June. This early-summer display draws bees and butterflies.

Western blue flag blooms purpleFoliage

Pollinators & wildlife

Bees Yellow-faced Bumble Bee

also Black-tailed Bumble Bee, Bombus fervidus, Hunt's Bumble Bee +11 more
Fuzzy-Horned Bumble Bee, Two-form Bumble Bee, Half-black Bumble Bee, Yellow-fronted Bumble Bee, Nevada Bumble Bee, Great Basin Bumble Bee, Yellowish Cuckoo Bumble bee, Indiscriminate Cuckoo Bumble Bee, Van Dyke's Bumble Bee, Osmia bella, Osmia longula
Butterflies Silver-spotted Skipper

also Western Tiger Swallowtail, Silvery Blue, Anise Swallowtail +4 more
Two-tailed Swallowtail, Rocky Mountain Parnassian, Macoun's Arctic, Polites sabuleti draco
Hummingbirds Broad-tailed Hummingbird
Also visited by
- Beetles: Acmaeodera connexa

Butterflies that use this plant

Documented host and nectar records. Each links to a planting guide for that butterfly.

Full plant details

Where it grows

Habitat: WetlandThe wild plant community it grows in.
Native range: The Pacific Coast, the Southwest, and the Rockies and southern CanadaUnited States (14): AZ, CA, CO, ID, MT, ND, NE, NM, NV, OR, SD, UT, WA, WY. Canada (2): AB, BC. Where it grows wild on its own, by state and province.
Native distribution: British Columbia to southern California (mostly east of the Cascades), east to the Dakotas, New Mexico and MexicoThe same native range, usually more exact than the state list, and often noting where it has spread beyond it.

Growing conditions

Light: Full sunHow much sun it takes, from full sun to full shade.
Moisture: WetThe soil dampness it prefers, from dry to wet.
Hardiness zones: USDA 2–9 · Canadian 1–7The cold-to-heat climate range it survives.
Soil: Wet soilsThe soils it grows in naturally.
Soil texture: Light to medium (sandy to loamy)The soil grade it prefers, from sand to clay.
Soil pH: 7.0–8.5The acidity to alkalinity it tolerates (7 is neutral).
Soil quality: LowHow rich a soil it needs. Many natives prefer lean soil and flop in rich beds.
Water use: HighHow thirsty it is, a rough guide to how often to water.
Salinity tolerance: NoneHow well it copes with salty soil, near roads or the coast.
Lime (CaCO₃) tolerance: HighHow well it copes with chalky, lime-rich soil.

Growth & form

Height: up to 2 ft (to 0.6 m)Typical mature height.
Spread: ~3 ft (1 m)How wide one plant gets, a guide to spacing.
Life cycle: PerennialWhether it lives a single season (annual), two (biennial), or returns for years (perennial).
Growth rate: RapidA relative ranking versus other plants of the same type (USDA), not an absolute rate.
Shape: ErectIts overall silhouette.
Root depth: 6+ in (15+ cm)How far the roots reach, a guide to drought resilience and transplanting.

Flowers, foliage & fruit

Type: WildflowerWhat kind of plant it is.
Bloom: May–JulWhen it flowers.
Flower color: PurpleThe bloom color, or colors.
Fruit/Seeds: Capsule; ripens May–SepThe seed or fruit it sets after flowering.
Toxicity: Poisonous if eatenWhether any part is poisonous to people or pets.

Propagation & seed

Cold stratification: Not requiredWhether seed needs a cold, moist spell before it will germinate.
Propagation: Bare root, bulb, corm, seedHow to start new plants.
Seed: ~0.0 million seeds per poundNotes on the seed and how to sow it.
Seed spread rate: ModerateHow readily it self-sows. Slow or none means well-behaved, not a spreader.
Seedling vigor: HighHow strongly young seedlings establish.
Vegetative spread: RapidWhether it creeps outward or stays put in a clump.