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Blue flag iris
Habit (mature) · U.S. Fish & Wildlife Service / Wikimedia Commons · Public domain
Limited coverage
Blue flag iris
Iris versicolor
A native eastern + central North American wetland iris producing striking violet-blue flowers with yellow + white throat markings in late spring + early summer. Tolerates wet feet better than most irises — among the best perennials for rain gardens, stream edges, and pond margins. Long-lived; clumps slowly expand. ALL parts of the plant are toxic (irisin glycoside) — wildlife typically avoid it; humans + pets can experience GI distress + skin irritation from sap contact.
Native: 29 US states + 1 CA province
Review: Source-backed
Climate fit: broad (90/100)
Focal point
Pollinator
Light
Full sun / Part sun
Water
Consistent moisture
Mature size
24-36" tall · 18" apart
Hardy in zones
3a-9b
brutally cold to frosty winters
Summer heat range
Cool-Hot
cool to hot summers Interim Plotwright tier until the plant AHS range is authored.
Native in Illinois
Yes
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Heat and sun protection
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Native across 30 US states and Canadian provinces — a wide-ranging part of North America's plant communities.
Lady Bird Johnson Wildflower Center
Cold hardiness
Now
Zone 6b
USDA
Chicago, IL · 1991-2020 average annual coldest day
Source: USDA Plant Hardiness Zone Map 2023 (1991-2020 climatology) via ArcGIS FeatureServer
Well-suited
2050
Zone 7b
Plotwright
Your zone + climate-model shift · SSP3-7.0 (regional rivalry)
Well-suited
In plain terms: cold winters — coldest nights typically around -3°F.
Well-suited today and still thriving in 2050.
Heat tolerance
Loading current AHS heat-zone and plant heat-fit data at your coordinates…
Sources & citations
Cite this page
For lesson plans, articles, or research that uses this page. To cite a single upstream fact instead, use its specific source listed below.
Plotwright. (2026, May 17). Blue flag iris (Iris versicolor). Retrieved 2026, June 5, from https://plotwright.garden/plants/blue-flag-iris
Sources for every fact
Every fact on this page traces to a source. 18 fields cited18 source-backed.
NC State Extension Gardener Plant Toolbox
University extension service
Backs 17 fields
Identity
Summary
Plant type
Light
Moisture
Hardiness
Heat zone
Size
Spacing
Habit
Design roles
Seasonal interest
Growth stages
Lifecycle
Regional guidance
Success tips
Designer notes
Wikimedia Commons
Photo · Public domain
Backs 1 field
Image
Community photos
The photos above are our reviewed reference set, curated for accuracy.
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