How to Grow, Maintain, and Divide Bearded Iris
Bearded iris is among the most elegant -- and easy to grow -- flowers of spring. Follow our tips for long-lasting, ever-multiplying blooms.
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.
Iris Growing Tips
- 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.)
How to Divide Bearded Iris'Avalon Sunset' (apricot); 'Throb'(yellow); 'Syncopation'(violet-orange, brown edges)
Bearded iris produce leaves, flower stems, and roots from a thick, rootlike structure called a rhizome. As the plant matures, the rhizome produces more rhizomes, which in turn lead to more leaves and flowers. Over time, however, the original rhizome withers and dies off. When this happens, bloom production slows and it is necessary to divide the plant, removing and replanting the baby rhizomes so they can develop.
Bearded iris should be divided in the late summer, when the weather starts to cool. The division process illustrated below can be used for other plants that produce rhizomes, including canna, bergenia, dahlia, toad lily, and lily-of-the-valley.
Step by Step
1. Carefully dig the clumps with a garden fork or spade, taking care not to chop into the rhizomes more than necessary.
2. Divide the rhizomes by pulling them apart with your hands. In some cases, you may need to use a sharp knife to separate the baby rhizomes from their mothers. If so, dip your knife into a 10-percent bleach/water solution between cuts.
A good rhizome will be about as thick as your thumb, have healthy roots, and have one or two leaf fans. Large, old rhizomes that have no leaf fans can be tossed.
Some Great Irises
Iris flowers have three primary structures, and descriptions of a variety often refer to these parts. For example, in the flower shown here, 'Fringe of Gold', the drooping "falls" are white edged (or picoteed) in yellow. The upright "standards" are solid yellow. And the tiny fuzzy "beard" in the middle is white. You can use these structure names to imagine how an iris might look when you have only a text description.
As a longtime lover of bearded iris, Doris Winstead has many favorite varieties, including 'Fringe of Gold'. See below for several more of here favorites.