Northern Blue Flag Plant Profile

Native Iris for Landscaping in Wet Areas

By David Beaulieu

Updated 05/08/19

Northern blue flag plants in bloom.
David Beaulieu

Northern blue flag is a member of the iris family more often seen in the wild than in landscapes. This is a shame because homeowners would find this attractive plant an ideal choice to grow along the margins of water features. It makes a big visual impact and requires little care.

More Plant Facts for Northern Blue Flag

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 to 9). But 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). Sweet flag (Acorus calamus) is a different plant altogether.

Northern blue flag is a clump-forming plant. Bluish-green, sword-shaped leaves arise out of the clump, and the flower stalk will bear three to five flowers. 

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.

The 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).

Light

Northern blue flag is best grown in full sun to partial shade.

Soil

It craves a soil rich in nutrients. Since this is a water plant, it is essential to keep the soil moist.

Water

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. In the wild, you will most likely find it growing around the margins (edges) of ponds, rather than in deep water. But it can stand in water as much as 2 to 4 inches deep.

Fertilizer

Compost is the ideal fertilizer to use since it is organic, free (if you have a compost bin), and will never burn your plants the way chemical fertilizers can.

More on Care, 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, it should not require much care on your part, other than mixing compost into the soil around it each spring to provide nutrition. Here are some of the specific potential uses for these perennials in your landscaping:

Wildlife and Northern Blue Flag, Its Name Origin

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

Both words in the botanical name of Iris versicolor refer to color. The genus name (which doubles as a common name) of 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 species name of versicolor means "having a variety of colors" and refers to the multiple colors on each flower of Northern blue flag.

In terms of etymology, the common name of "flag" comes from the Middle English, flagge, meaning "reed," 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.

Kinds of Irises Commonly Grown in Landscaping

In addition to these wild flag plants, there are many cultivated types of irises popular in landscaping, including: