Of the many native irises from the Iridaceae family in North America, Iris versicolor (EYE-ris VER-suh-kuh-lor) is one of the most famous. This herbaceous perennial is the official flower of Québec, Canada, and is found growing naturally from Manitoba to Nova Scotia in the north, and Virginia to Minnesota in the south.
This plant goes by several nicknames, including:
- Blue flag iris
- Harlequin blue flag
- Larger blue flag
- Northern blue flag
- Purple iris
The word “flag” in the common name is derived from the Middle English word flagge, which means reed or rush, and is a reference to its habit of thriving in standing water.
A similar species, southern blue flag (Iris virginica), is less tolerant of water in winter and grows in the warmer regions of the United States.
Large Blue Flag Care
Size & Growth
In gardens, blue flag is a clumping flower which grows to 2’ to 3’ feet tall and wide. However, in ideal growing conditions, the height may be as tall as 4’ feet.
The sword-shaped green leaves are 20” to 40” inches long and up to 2” inches wide, with prominent veins and a green to greyish green coloration. They tend to rise in a roughly fan shape from the base, eventually drooping from their own weight. A few short leaves may also appear on the stem, but are completely absent from the flower stalks.
Flowering and Fragrance
This iris flowers in May and June, but bloom time can last well into August in the right conditions. It’s best known for having violet-blue flowers, although the bloom color can range between blue, deep blue, violet, purple, and on rare occasion white.
They feature purple veins and a yellow and white patch at the center.
The inflorescence tends to have 2” to 4” inch wide flowers per stalk. It has three larger drooping petals known as sepals, and three shorter, erect petals known as standards. A gland at the base of the petals produces nectar.
A 1 ½” inch long capsule forms in the middle of the flower, containing two rows of brown, D-shaped seeds on each side. The capsule eventually opens, allowing the seeds to be wind-sown.
Light & Temperature
Violet blue flag loves either full sun or part shade, although too much shade may prevent flowering.
The plant thrives in USDA hardiness zones 2 to 7, although a little mulch layer towards winter will help protect younger specimens from the cold.
Watering and Feeding
As a marginal aquatic plant, blue flag is quite comfortable in conditions similar to the sedge and wet meadows it came from. High soil moisture or humidity allow the plant to grow in less swampy environments.
As part of a water feature, it can stand in water as deep as 6” inches. Be sure to place mulch around the plant to keep the soil moist when growing away from water.
Rich, organic soils are best for this plant, and adding compost every spring is one of the best ways to feed this iris.
Soil & Transplanting
While Iris versicolor prefers a rich, loamy soil, it can adapt to most types of soil so long as they’re kept moist or wet.
Grooming And Maintenance
This plant doesn’t require much maintenance, although damaged, diseased, or dead parts should be removed in the fall to aid in overwintering.
Recommended Reading On Iris
How To Propagate Purple Iris
The seeds of blue flag need to be stratified by a period of cold exposure before they’ll germinate. In nature, the seeds spread and overwinter, but you can emulate this process by refrigerating seeds in a container or damp wrapping.
It’s best to sow them in the fall, as they require a minimum of 120 days before they’ll germinate. Simply find a sheltered place in the garden and cover in ⅛” inch of compost.
You can also artificially wake the seeds by soaking them in warm water for 24 hours, allowing the water to cool during the process. Seeds generally take between 30 and 180 days to germinate.
Seedlings must be kept moist and indoor plants should be potted once they are large enough to handle. Plant seedlings ½ to ¾” inches deep.
The plant will also self-seed or create colonies thorough spreading rhizomes if left alone. You can gently divide the rhizomes to propagate manually before late spring so long as you wear gloves.
Iris Versicolor Blue Pests or Diseases
Both the rhizomes and rootstocks are skin irritants and mildly toxic if ingested. Symptoms include abdominal pain, diarrhea, fever, nausea, and vomiting. The plant is poisonous to both livestock and pets.
The plant is deer resistant. It is also flood resistant, able to withstand total submersion for brief periods of time. It’s mildly drought tolerant.
There are few pest or disease problems with this plant. The Iris Borer is one of the most serious insect pests.
Suggested Blue Flag Uses
Blue flag soaks up excess nutrients from any water source it grows in, allowing it to improve water quality. It attracts a wide range of wildlife and pollinators, including bees, birds, and hummingbirds.
The rhizome, while mildly toxic, is dried and used in traditional Native American medicine as a cathartic and diuretic in carefully controlled amounts.
The rhizome is also used in perfumes while the leaves produce tannin for natural dyes. The two outermost fibers of the leaves can be spun into a very fine, high quality twine used in Native American crafts.
As a garden plant, it excels as a border for water features or in rain gardens. The role of irises as a symbol of their namesake Greek goddess who delivered messages using rainbows also makes this plant perfect for Classical-themed garden displays.