Northern Blue Flag

Native Iris for Landscaping in Wet Areas

Northern blue flag plants in bloom.
David Beaulieu

What Is Northern Blue Flag?

Northern blue flag is an herbaceous perennial. Its botanical designation is Iris versicolor. The geographical element in its common name distinguishes it from Southern blue flag (Iris virginica), which, predictably, is the less cold-hardy of the two plants (growing zones 5-9). Both perennials are indigenous to eastern North America. Yellow flag (Iris pseudacorus) grows wild in eastern North America but is not native (it is invasive). Take note that sweet flag (Acorus calamus) is a different plant altogether.

Plant Description

Iris versicolor attains a height of 2-3 feet, with a similar spread (I have found it more often on the lower end of that spectrum here in New England). Sword-shaped leaves arise out of a clump, and the flower stalk will bear 3-5 flowers. Depending on where you live, it will bloom in May or June. The plants shown in bloom in the picture above were growing in a wetland area of Acadia National Park, Maine; I took the photo in June.

From a distance, the flower appears simply a violet-blue color. Viewed up-close, however, you will detect purple veins. Moreover, there is yellow and white on the falls.

Plants spread via rhizomes to form colonies. Although traditionally used in medicine by herbalists, these rhizomes are poisonous, so handle them with gloves if you will be dividing this perennial to propagate it (spring division is usually recommended).

Growing Conditions for Northern Blue Flag

Observing the plant in its wild habitat will lend a clue as to its optimal growing conditions in your landscaping. This type of iris is considered one of the "marginal" aquatics. That is, in the wild, you will most likely find it growing around the margins (edges) of ponds, rather than in deep water. 

Northern blue flag is best grown in planting zones 3-9 in full sun to partial shade. It craves a wet soil fortified with abundant humus. 

Northern Blue Flag and Wildlife

This wild iris is a deer-resistant perennial. Bambi's loss is Hummer's gain: it is a good hummingbird plant.

Origins of the Names

Both words in the botanical name, Iris versicolor refer to color. The genus name (which doubles as a common name), Iris references the goddess of the rainbow in Greek mythology. That genus does, indeed, furnish us with some of the most vibrant colors in our landscapes, which is one reason why irises have so long been a favorite with gardeners. Meanwhile, the specific epithet, versicolor means "having a variety of colors" and refers to the multiple colors on each flower of Northern blue flag (see above).

The dictionary gives the etymology of the common name, "flag" as coming from the Middle English, flagge, meaning "reed," and going back to a Scandinavian term. The connection may not be immediately apparent, but Northern blue flag does inhabit the same environs in the wild as reeds do, so perhaps it is a matter of association.

Uses in Landscaping

A tough plant, consider Northern blue flag as a possible component in your low-maintenance landscaping plan. Given the right growing conditions (see above), it shouldn't require much care on your part. Here are some of the specific potential uses for these perennials in your landscaping:

Kinds of Irises Commonly Grown in Landscaping

In addition to the wild flag plants mentioned in this article, there are, of course, many cultivated types of irises popular in landscaping. Consult the following articles to learn about some of them: