I bought blue flag for a spot near our front door that was flooded by every hard rain. I knew the elegant purple-blue flowers of this native iris would be a pretty sight in spring—but even better are the long, tapered, swordlike leaves, which last until fall and make a great background for smaller summer flowers. Blue flag (Iris versicolor) does best in water gardens or at the edges of ponds and streams, but it will also do well in a regular garden bed that has consistent moisture. After I planted blue flag, we installed gutters, and the soggy patch is no longer soggy. The blue flag is doing fine, though—in fact, it’s about to outgrow its home.
Common name: Blue Flag
Botanical name: Iris versicolor
Plant type: Perennial
Zones: 3 to 9
Height: 2 to 3 feet
• Sun: Full sun to part shade
• Soil: Average, humusy
• Moisture: Medium to wet
• Mulch: Mulch to preserve moisture in the soil.
• Pruning: None needed.
• Fertilizer: None needed.
• By division
Pests and diseases
• Vulnerable to crown rot, leaf spot, rust, and viruses.
• Common pests include aphids, iris borers, whiteflies, and snails and slugs.
• Iris versicolor does well on the edges of a pond, water garden, or bog. Or plant it in a border with rich, consistently moist soil.
• Plant with turtlehead, ferns, swamp milkweed, and other moisture-loving plants.
• Leave the stems and seed pods of blue flag. When they dry, they’ll create an interesting winter scene.
• I. versicolor will spread slowly to form clumps. You can divide them every third year.
• ‘Kermesina’ has purple-red flowers.
• ‘Mint Fresh’ has white petals with purple stripes.
• The flowers of ‘Version’ are a soft pink color.
All in the family
• There are more than 300 species in the Iris genus.
• Blue flag has a southern cousin, Iris virginica, which is similar in appearance and habit, but thrives in Zones 5 to 9.
• Also in the Iridaceae family are the genera Crocus, Gladiolus, and Sisyrinchium.
(Text by Elizabeth Noll, photo of Iris versicolor courtesy of Missouri Botanical Garden’s Kemper Center for Home Gardening)