Blue flag iris
Iris versicolor · Iridaceae
The native wetland iris: violet-blue flowers veined with yellow and white on branching stems in early summer, above sword-like leaves.
- Size
- 2½ ft tall, 24 in wide
- Zones
- 3 to 9
- Light
- Full sun to part sun
- Flowers
- Late May to late June
- Pets
- Toxic (mild)
- Job in a bed
- Accent
A bed built around blue flag iris
The planner designed this bed around blue flag iris when this page was made: a 12 × 6 ft (3.7 × 1.8 m) English border in zone 6, full sun. It chose the other plants from the 251 that suit those conditions and its wet soil, and says below why blue flag iris stands where it does.
The plants
- 1 Blue flag iris × 2, blue
- 2 Lingonberry × 6, pink
- 3 Mouse-ear coreopsis 'Nana' × 24, yellow
- 4 Garden phlox 'David' × 3, white
- 5 Globe arborvitae 'Danica' × 1, green leaves
- 6 Turtlehead 'Hot Lips' × 3, pink
- 7 Checkered lily × 12, purple
Why this plant
- The only blue.
Why here
- In the middle. At 2½ ft it is the step between mouse-ear coreopsis 'Nana' (8 in) in front and garden phlox 'David' (3½ ft) behind: each is seen over the one before.
- 2 plants in 2 places. An accent is a punctuation mark: the repeat along the bed gives it rhythm.
Why now
- In flower for four weeks. From late May to late June.
- Fills a gap. For one of those weeks nothing else on the plan is in flower.
Planned as an English border: 5 of the 7 groups (71%) are drifts, longer along the bed than they are deep. Garden phlox 'David' and turtlehead 'Hot Lips' anchor the back corners of the bed: the tallest plants on the plan stand there. There is more mouse-ear coreopsis 'Nana' than anything else, 24 plants in all.
The planner's own design check: 11 Excellent, 5 Good, 1 Satisfactory. It flags one thing to watch: Nothing on this plan is highly poisonous or an aggressive spreader.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where blue flag iris goes in a border
At 2½ ft it belongs in the middle of a bed. In the planner's ten height classes it is medium (24 in to 2½ ft).
Its job: accent. An upright plant used singly, like a punctuation mark, and repeated at intervals to give the bed rhythm.
Plant this wherever the invasive yellow flag iris might be considered: it gives the same sword-leaved clump in wet soil, in a better colour, and it belongs here.
- Pond edges and rain gardens
- A native substitute for the invasive yellow flag
- Wet meadows
What to plant with blue flag iris
Plants recorded as good partners for it, and what each pairing does:
- Marsh marigold: flowers first, mid April to early May, so the spot is never empty; low enough (16 in) to stand in front of it; happy in the same wet soil.
- Swamp milkweed: takes over when it finishes, flowering from early July; tall enough (4 ft) to stand behind it.
- Cardinal flower: takes over when it finishes, flowering from late July; happy in the same wet soil.
Questions about blue flag iris
Does blue flag iris need sun or shade?
Blue flag iris grows in full sun (6 or more hours of direct sun a day) and part sun (4 to 6 hours of sun, including some afternoon sun).
It wants moist to wet soil, rich in organic matter, and plenty of water. It copes with soil that stays wet.
What zones does blue flag iris grow in?
USDA zones 3 to 9. It is hardy to zone 3, which means it survives winter nights down to about −30 °F (−34 °C).
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does blue flag iris flower in my zone?
In zone 5 it flowers late May to late June. As a spring flower it moves about a week for every zone: earlier where it is warmer, later where it is colder.
| Zone 3 | Mid June to late June |
|---|---|
| Zone 4 | Early June to late June |
| Zone 5 | Late May to late June |
| Zone 6 | Late May to late June |
| Zone 7 | Mid May to mid June |
| Zone 8 | Early May to mid June |
| Zone 9 | Early May to early June |
Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.
How far apart should blue flag iris be planted?
18 in (45 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 24 in (60 cm), so a group knits into one patch.
It grows 2½ ft (75 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many blue flag iris plants do I need?
At 18 in apart, set out in staggered rows:
- 5 to fill 10 square feet (about 1 m²)
- 7 for a single row 10 ft (3 m) long
- 17 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as one at a time, repeated along the bed at intervals; a slender one reads better as a clump of three.
In the bed above, the planner used two in two groups.
Is blue flag iris poisonous to dogs and cats?
Yes: mild toxicity to people, dogs, cats and horses. The underground stems (rhizomes) and leaves can cause drooling and stomach upset if eaten.
Rated from NC State Extension and the ASPCA. Where references disagree, the more cautious rating is used.
Do deer eat blue flag iris?
Mostly not. NC State lists it as resistant to deer. No plant is proof against a hungry deer in a hard winter, but this one is low on the menu.
What flowers after blue flag iris?
Blue flag iris is over by late June. These start as it finishes and carry the same spot on, so it never goes flat:
- Swamp milkweed: from early July to early August, 4 ft tall (a recorded partner).
- Black-eyed Susan: from mid July to mid September, 24 in tall.
- Yarrow: from mid June to late August, 24 in tall.
What does blue flag iris look like in winter?
Blue flag iris dies down to the ground and there is nothing to see until spring. The old stems can be cut in autumn, or left until spring as shelter for overwintering insects.
More Iris
- Bearded iris Iris x germanica
- Bearded iris 'Immortality' Iris 'Immortality'
- Blackberry lily Iris domestica
- Dutch iris Iris x hollandica
- Dwarf bearded iris Iris pumila
- Dwarf crested iris Iris cristata
- Iris 'Katharine Hodgkin' Iris 'Katharine Hodgkin'
- Japanese iris Iris ensata
- Louisiana iris Iris (Louisiana hybrids)
- Netted iris Iris reticulata
- Roof iris Iris tectorum
- Siberian iris Iris sibirica
- Siberian iris 'Caesar's Brother' Iris sibirica 'Caesar's Brother'
- Southern blue flag Iris virginica
- Sweet iris 'Variegata' Iris pallida 'Variegata'
- Variegated Japanese iris Iris ensata 'Variegata'
- Yellow flag iris Iris pseudacorus
In these guides
- Plants for wet soil and rain gardens
- Deer-resistant perennials for full sun
- Garden plants toxic to cats
- Garden plants toxic to dogs
- Garden plants native to Canada
- Plants with blue flowers
Zone guides: Zone 3 · Zone 4 · Zone 5 · Zone 6 · Zone 7 · Zone 8 · Zone 9
Every fact on record
- Type
- Perennial
- Size
- 2½ ft (75 cm) tall, 24 in (60 cm) wide
- Plant
- 18 in (45 cm) apart
- Height class
- Medium (24 in to 2½ ft)
- Place in the bed
- Middle
- Flowers
- Late May to late June; blue
- Leaves
- Medium texture, herbaceous; green
- Shape
- Upright, spreading
- Hardy in
- USDA zones 3 to 9
- Light
- Full sun, part sun
- Soil
- Rich, moist to wet
- Water
- High
- Feeding
- None needed
- Family
- Iridaceae
- Comes from
- Central & Eastern Canada to North Central & Eastern U.S.A
- Stands up to
- Deer, wet soil
Checked against NC State Extension, ASPCA poison lists and VASCAN (plants of Canada). Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.