It's a magical time when bearded irises unfurl their pencil-slim buds to reveal a kaleidoscope of color in spring. Once commonly called flags, these perennials flourish in USDA Zones 3-9, where winter temperatures dip below freezing and allow the plant to go dormant before next year's growth.
"Anyone can grow iris," says Doris Winton, who has had a lifelong attraction to the flower and is a master judge for the American Iris Society. While fragrance has diminished through hybridization, the size of blooms has increased, as has the palette. "Every color -- except fire-engine red -- can be found in bearded iris," Doris says.
Below are Doris's tips for growing outstanding bearded iris.
- Plant them in a sunny spot in late summer. The plants need well-drained soil and at least six hours of sunlight per day. A full day of sun is even better to keep the rhizomes dry. (The rhizomes are the fleshy rootlike structures at the base of the plant.)
- Prepare their beds. Doris recommends a low-nitrogen fertilizer and a soil pH slightly less than 7, which is neutral. She applies a granular fertilizer twice a year -- in early spring and just after bloom when the rhizomes are forming the next year's flowers. Water only if it is extremely dry or after transplanting.
- Give them room to breathe. Bearded iris require good air circulation. Plant them a minimum of 16 to 18 inches apart (less space for dwarf irises and more for taller varieties).
- Do not mulch. Mulching retains moisture, and too much moisture will cause soft rot of the rhizomes.
- Break off seedpods that form after the blooms have faded. This prevents seedlings from choking the surrounding soil. Seed formation also saps energy needed by the rhizomes, roots, and leaves.
- Prune back the foliage in the fall. This will reduce the chances of overwintering pests and diseases.
- Make dividing a habit. Divide clumps of bearded iris every three to four years in the late summer. (See the next page for detailed instructions on dividing and replanting bearded iris.)