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Naturally found in marshes, flood plains, and edges of water bodies, Southern blue flag provides excellent soil stabilization. Photo credit:Robert H. Mohlenbrock @ USDA-NRCS PLANTS Database / USDA NRCS. 1995. Northeast wetland flora: Field office guide to plant species. Northeast National Technical Center, Chester.

Naturally found in marshes, flood plains, and edges of water bodies, Southern blue flag provides excellent soil stabilization.
Photo credit:Robert H. Mohlenbrock @ USDA-NRCS PLANTS Database / USDA NRCS. 1995. Northeast wetland flora: Field office guide to plant species. Northeast National Technical Center, Chester. USDA, NRCS. 2012. The PLANTS Database (http://plants.usda.gov, 8 October 2012). National Plant Data Team, Greensboro, NC 27401-4901 USA.

Iris virginica

Southern blue flag

Plant Highlight:

Iris virginica (Southern Blue Flag)

FIRST IMPRESSIONS:  Iris virginica is a robust perennial that forms small colonies from a network of underground rhizomes.  Plants produce clumps of distinctive narrow pointed leaves. In late spring, foliage is topped by lovely blue irises. This unique wildflower thrives in sunny moist or wet sites.

HABITAT & HARDINESS:  Iris virginica is native to wetlands in the coastal plain from Virginia to Florida and Texas.

This iris is indigenous to marshes, swamps, wet meadows, wet pinelands, margins of ponds and creeks, sedge meadows and borders of wetland forests.

Plants are hardy in USDA Zones 5-9.

PLANT DESCRIPTION:  Iris virginica grows in large clumps that originate from thick creeping rhizomes.  

The sword shaped leaves are about 24” tall and 1-2” wide.  Leaves overlap at the base and fold around the adjacent leaf to form a flat fan-like arrangement.  The blades often lie on the ground or in the water.

In spring leafless flower stalks bear 2-6 blue-purple or violet flowers.  Each bloom is 3-4” wide with darker purple veins.  Flower color varies from pale blue, purple, violet and lavender.

The blooms have a typical iris form with 3 drooping sepals called “falls” and 3 small upright petals called “standards”.   The falls are marked with a yellow blotch surrounded by a white border.  

Angular capsules form after flowering.  The seeds inside can float and are distributed by water.

Plants are 2’ tall with a 2-3’ spread.

CULTURAL & MAINTENANCE NEEDS:  Iris virginica grows best in sunny sites.  Plants tolerate part shade but may not bloom well. 

This versatile wildflower prospers in moist or wet sandy acidic soils that are high in organic matter.  Plants also thrive in average garden soils and 2-4” of standing water.  Like other wetland iris, this one filters excess nutrients from ponds and creeks and can improve the water quality.

Plants appreciate a layer of mulch to protect the shallow rhizomes from sunburn. This species is somewhat pest resistant and foliage is unpalatable to deer and other herbivores.

LANDSCAPE USES:  Iris virginica is an excellent Accent for a Water Garden or Stormwater Detention Basin.  Small Groups or Masses of plants offer Attractive Foliage, Showy Flowers, Cut Flowers and provide Erosion Control.  This species is a valuable component of Cottage Gardens, Deer Resistant Plantings, Low Maintenance Plantings, Perennial Borders, Rain Gardens, Wetlands and Wildlife Gardens.

COMPANION & UNDERSTUDY PLANTS:  Iris virginica mingles cheerfully with Asclepias incarnata, Carex muskingumensis, Chelone glabra, Eupatorium perfoliatum, Osmunda cinnamomea and Rhexia virginica.

Iris versicolor could be substituted in wetlands in the northern part of the range.

TRIVIA:  Flowers are pollinated by native bees, visited by butterflies and attractive to hummingbirds.

Iris versicolor is a similar species that occurs in the northern part of the Iris virginica range, in wetlands around the upper Great Lakes, in the Northeastern U. S. and into Canada.  Iris versicolor is taller to 3’ or more with leaves that are upright rather than flopping on the ground or in the water.

Iris virginica var. shrevei is native to inland swamps, marshes and flood plains of the Ohio Mississippi Rivers and around the Great Lakes. This subspecies is similar in appearance to Iris virginica but is hardy further north and is reported to prefer soils with pH closer to neutral.


Height:

2 ft

Spread:

2-3 ft

USDA Hardiness Zone:

5-9

Bloom Color:

Blue

Iris virginica Characteristics

Exposure

  • Full Sun to Partial Shade

Critter Resistance

  • Deer Resistant

Attracts Wildlife

  • Butterflies
  • Pollinators

Soil Moisture Preference

  • Wet to Moist

Attributes

  • Naturalizing
  • Bog

Flowering Months

  • June
  • May

Foliage Color

  • Green

Season of Interest (Foliage)

  • Summer
  • Spring

Growth Rate

  • Fast

Salt Tolerance

  • None

Phytoremediation

  • TCE-trichloroethyleneand by-products
  • TCE-trichloroethylene

Interesting Notes:

For more information on this plant, visit the USDA PLANTS Database: http://plants.usda.gov/java/profile?symbol=IRVI


Plants that work well with Iris virginica ''

Sweet flag Sweet flag (Acorus americanus)
Bristly sedge Bristly sedge (Carex comosa)
Fringed sedge Fringed sedge (Carex crinita)
Emory's sedge Emory's sedge (Carex emoryii)
Bristly cattail sedge Bristly cattail sedge (Carex frankii)
Porcupine sedge Porcupine sedge (Carex hystericina)
Lurid sedge Lurid sedge (Carex lurida)
Pink turtlehead Pink turtlehead (Chelone lyonii 'Hot Lips')
Boneset Boneset (Eupatorium perfoliatum)
Meadow beauty Meadow beauty (Rhexia virginica)
Cinnamon Fern Cinnamon Fern (Osmunda cinnamomea)
Path rush Path rush (Juncus tenuis)
Soft rush Soft rush (Juncus effusus)
Scouring Rush Scouring Rush (Equisetum hyemale)
Cattail sedge Cattail sedge (Carex typhina)
Lake sedge Lake sedge (Carex lacustris)

Substitutions for Iris virginica

Blue flag Blue flag (Iris versicolor)
Blue flag Blue flag (Iris versicolor)