Yellow Flag Iris, Yellow Iris, Water Flag Iris 'Roy Davidson'

Iris pseudacorus

Family: Iridaceae (eye-rid-AY-see-ee) (Info)
Genus: Iris (EYE-ris) (Info)
Species: pseudacorus (soo-DA-ko-rus) (Info)
Cultivar: Roy Davidson
Hybridized by B. Hager
Registered or introduced: 1987
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Louisiana (LA)



24-36 in. (60-90 cm)


12-15 in. (30-38 cm)

15-18 in. (38-45 cm)


USDA Zone 4a: to -34.4 C (-30 F)

USDA Zone 4b: to -31.6 C (-25 F)

USDA Zone 5a: to -28.8 C (-20 F)

USDA Zone 5b: to -26.1 C (-15 F)

USDA Zone 6a: to -23.3 C (-10 F)

USDA Zone 6b: to -20.5 C (-5 F)

USDA Zone 7a: to -17.7 C (0 F)

USDA Zone 7b: to -14.9 C (5 F)

USDA Zone 8a: to -12.2 C (10 F)

USDA Zone 8b: to -9.4 C (15 F)

USDA Zone 9a: to -6.6 C (20 F)

USDA Zone 9b: to -3.8 C (25 F)

USDA Zone 10a: to -1.1 C (30 F)

USDA Zone 10b: to 1.7 C (35 F)

Sun Exposure:

Full Sun


Parts of plant are poisonous if ingested

Bloom Color:

Bright Yellow


Bloom Time:

Extra early (EE)

Midseason (M)

Late Midseason (MLa)



Other details:

May be a noxious weed or invasive

Soil pH requirements:

5.6 to 6.0 (acidic)

6.1 to 6.5 (mildly acidic)

6.6 to 7.5 (neutral)

7.6 to 7.8 (mildly alkaline)

Patent Information:

Unknown - Tell us

Propagation Methods:

By dividing rhizomes, tubers, corms or bulbs (including offsets)

Seed Collecting:

N/A: plant does not set seed, flowers are sterile, or plants will not come true from seed

Awards (if applicable):

Unknown - Tell us

Foliage Color:

Unknown - Tell us

Bloom Characteristics:

This plant is attractive to bees, butterflies and/or birds

Water Requirements:

Very high moisture needs; suitable for bogs and water gardens

Where to Grow:

Unknown - Tell us


This plant has been said to grow in the following regions:

San Leandro, California

Sebastopol, California

Mathews, Virginia

Vancouver, Washington

Gardeners' Notes:


On Sep 5, 2015, Tygywoo from Sebastopol, CA wrote:

This iris is also drought tolerant! When I planted it, I thought it more closely related to spuria iris and put it in a full sun spot with very little water. You can't kill this thing! Increases and blooms every year, even without dividing for years.


On Jun 6, 2011, Jasmine6 from Mathews, VA wrote:

Just don't plant this where it can get away from you!! I planted a couple near my marsh in Virginia, and it has almost completely taken over, muscling out the cattails and other native plants. Pretty flower, but I'm sorry I ever saw it.


On May 17, 2007, Joan from Belfield, ND (Zone 4a) wrote:

Roy Davidson is an Apogon hybrid. Holden Clough open pollinated


On May 27, 2006, dmj1218 from west Houston, TX (Zone 9a) wrote:

Bright yellow flowers, with some veining and dark brown crescent signals, blooms on branched stems. Foliage is a lush green all summer long. Tall, vigorous grower.