Blue Flag Iris is a perennial grown for its blooms, which open in summer and return year after year. It's hardy across USDA zones 3 through 9 and shrugs off deer. Its summer flowers are a moderate draw for native bees and butterflies.
Blue Flag Iris — the short answer
Blue Flag Iris: grown in zones 3–9.
- USDA zones
- 3–9
- Manual horticultural correction (source not retained); NC State Extension and Missouri Botanical Garden, with the remaining rows from other published sources or Growable Ground compilation
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — each tile names its own row's source, because per-field provenance varies.
Score Blue Flag Iris on your exact land.
Zone averages can't see the slope, soil, frost, and sun that decide whether blue flag iris actually takes — and those shift from one yard to the next. Enter your address and we'll score blue flag iris against your land's real conditions.
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See Blue Flag Iris
What Blue Flag Iris is
Blue Flag Iris grows as a perennial and reaches around 2.5 feet at maturity. It blooms in summer. It's also deer-resistant.
How to grow Blue Flag Iris
Blue Flag Iris grows in USDA zones 3 through 9.
USDA Zones
3-9
USDA PHZM 2023
Soil pH
Data pending
Sun
Data pending
Growable Ground plant catalog
Drainage
Data pending
Growable Ground plant catalog
Mature Height
2.5 ft
Growable Ground plant catalog
Frost-Free Days
0+
The frost-free stretch it needs start to finish — short-season areas may need an indoor head start.
Growable Ground plant catalog
Start the season right
Plant blue flag iris in full sun.
Match the soil
Pull a soil test from your local Extension lab to confirm pH and drainage match blue flag iris's needs before planting.
Water steadily
Keep the root zone evenly moist through establishment. Match watering to the plant's drainage preference and your local rainfall.
Harvest at its peak
Cut blue flag iris blooms in the cool of the morning, just as they open, for the longest display.
Where Blue Flag Iris thrives
Blue Flag Iris is hardy across USDA zones 3 through 9. Zone is only the starting point, though: the soil pH, drainage, and frost dates on your specific land decide how well it actually does.
A USDA zone is a 10°F band of average annual extreme winter minimum, so zones 3–9 spans average winter lows from -40°F to 30°F (USDA PHZM 2023). Across the 50 states and DC, that band covers 42 outright and splits 9 more down the middle — and which side of that line your land sits on changes the answer.
Zones 3–9·Where Blue Flag Iris growsOpen map →
Where Blue Flag Iris stands, state by state
Blue Flag Iris is rated for zones 3–9 — a cold floor USDA puts at -40 to -30°F. Across the 50 states and DC, 42 sit fully inside that band, the line runs through 9 more, and 0 sit outside it — and inside every split state, the same line runs on at county grain.
Fully inside zones 3–9
42 states
3 of 42 shown
The line runs through
9 states
- Alaska · zones 1a-9a
- California · zones 4b-11a
- Nevada · zones 4a-10a
3 of 9 shown
Blue Flag Iris’s band covers part of each of these states — which side of the line your county sits on changes the answer, and each state page draws it.
State zone extents: USDA Plant Hardiness Zone Map (PHZM) 2023. A zone is a 10°F band of average annual extreme minimum temperature, so a state that splits the band contains the boundary — its own page draws the county line, and a parcel report resolves which side your land sits on.
What grows around Blue Flag Iris
Growing guides for blue flag iris
In rotation planning, blue flag iris counts as a Other — beds recover best when other crops don’t follow each other in the same spot year over year. (Growable Ground derivation — crop-rotation group from botanical family)
Related plants in perennial flower
Good to know
One caution for pet owners — blue flag iris is toxic to dogs and cats (moderate severity). Keep it out of reach, and call ASPCA Animal Poison Control at (888) 426-4435 in an emergency. (Source: ASPCA.)
Blue Flag Iris offers moderate value to bees and other pollinators. (Source: Lady Bird Johnson Wildflower Center.)
Your land is one point inside Blue Flag Iris's range
This page resolves to the species. Your state page draws the county line, and a report reads the parcel — the soil pH, drainage, sun, and frost dates on your exact ground, which no species average can see.
See if Blue Flag Iris will thrive on your land
Zone averages are a start. Your exact soil pH, drainage, sun exposure, and frost dates shape whether blue flag iris actually takes — we score it against the real conditions at your address.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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How we know this about Blue Flag Iris
The figures above are cited per row, not per site: the pH band names this plant’s own source column, the three temperature figures each carry their own, and days-to-maturity cites the publication that actually lists it. All of it comes from the Growable Ground Plant Database — a compilation over FAO ECOCROP, USDA PLANTS, and university Extension sources, published openly with per-field provenance.
Grounded inUSDA PLANTS Database•USDA PHZM•ASPCA
Frequently asked questions
Can I grow Blue Flag Iris in my zone?
Blue Flag Iris grows in USDA hardiness zones 3 through 9 (USDA PHZM 2023). Zone is one factor — soil pH, drainage, and frost dates on your specific parcel also shape whether it takes.
When should you plant Blue Flag Iris?
Time blue flag iris to your own season rather than the calendar. Your local frost dates set the exact window — a Growable Ground report reads them for your address.
What soil does Blue Flag Iris need?
Specific pH data for blue flag iris is pending. A soil test from your local Extension lab confirms what your site needs.
Does Blue Flag Iris attract pollinators?
Yes — blue flag iris's flowers are a solid nectar source for native bees and butterflies. (Source: Lady Bird Johnson Wildflower Center.)
Is Blue Flag Iris safe for pets?
Blue Flag Iris is toxic to pets (dogs,cats) with moderate severity. Keep it out of reach, and call ASPCA Animal Poison Control at (888) 426-4435 in an emergency. (Source: ASPCA.)