How to Grow Bearded Iris for a Garden Full of Color
Bearded irises are among the most elegant and colorful perennials you can grow. With a little know-how, you can grace your garden with long-lasting, ever-multiplying blooms for years to come.
It's a magical time when bearded iris flowers unfurl their pencil-slim buds to reveal a kaleidoscope of color, beginning as early as March in warmer regions. Depending on the type of bearded iris, they can be in bloom all the way into June. Some types even rebloom in late summer and fall. These hardy 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 this plant and is a master judge for the American Iris Society. It's easy to understand why people have such passion for iris—it's a very diverse group of plants, with bearded iris being one of three main categories. This kind of iris gets its name from a patch of soft bristles on the lower petals of the flowers. In addition to their long bloom time, bearded iris come in an incredible variety of colors and patterns. "Every color—except fire-engine red—can be found in bearded iris," Winton says.
Iris Growing Tips
No matter which varieties you choose to grow, there are a few things you can do to help bearded irises thrive in your garden. Follow these tips for the healthiest plants and best blooms:
- 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. Use a low-nitrogen fertilizer and apply it twice a year: In early spring and just after bloom when the rhizomes are forming the next year's flowers. Only water only if it's extremely dry or after transplanting.
- Give them room to breathe. Bearded iris need good air circulation. Plant them a minimum of 16 to 18 inches apart (less space for dwarf irises and more for tall bearded iris varieties).
- Do not mulch. Mulching helps the soil retain moisture, and too much moisture will cause the rhizomes to rot.
- Remove 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 plants every three to four years in late summer.
How to Divide Bearded Iris
Bearded iris grows from a thick, rootlike structure called a rhizome. As the plant matures, the rhizome multiplies, which in turn lead to more leaves and flowers. But over time, the original rhizome withers and dies off, which can slow how quickly the plant produces new blooms. When this happens, it's necessary to divide the plant, removing and replanting the newer rhizomes so they have the space they need to fully develop.
Bearded iris should be divided in the late summer when the weather starts to cool. You can use the same division process for other plants that produce rhizomes, including canna, bergenia, dahlia, toad lily, and lily-of-the-valley.
Carefully dig the clumps with a garden fork or spade, taking care not to chop into the rhizomes more than necessary.
Divide the rhizomes by pulling them apart with your hands. In some cases, you might need a sharp knife to separate the smaller rhizomes from the main one. If so, dip your knife into a 10-percent bleach/water solution between cuts so you don't spread any diseases to new rhizomes.
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 out.
Wash the soil off the rhizomes so you can inspect each one for iris borer (a plump, white worm). If you find a borer, destroy it. Some gardeners like to wash their iris rhizomes in a 10-percent bleach solution to protect against disease, but that won't help plants that are already rotting. Make sure to discard any soft, smelly rhizomes you find, as well as any that feel lightweight or hollow, or that look dead, like the rhizome shown above.
Clip off the leaf blades so that they're 4 to 6 inches long. This reduces the stress that the plant goes through as it concentrates on regrowing new roots instead of trying to maintain long leaves.
Replant divisions, setting the rhizome higher in the planting hole than the fine roots, which should be fanned out. A bit of the top surface of the rhizome should be just visible at the soil surface.
Space the plants 12 to 18 inches apart (closer for dwarf varieties, farther apart for the largest). For the best display, plant the rhizomes so the fan of leaves face the same direction. Water well when planting bearded iris rhizomes, but don't continue to water unless the weather becomes dry.
Top-Performing Bearded Iris Varieties
Iris flowers have three primary structures, and usually, variety names are inspired by unique characteristics of one of the parts. For example, the 'Fringe of Gold' flower has drooping "falls" that are white-edged (or picoteed) in yellow. The upright "standards" are solid yellow. And the tiny fuzzy "beard" in the middle is white and yellow. If you've only got a description, you can use the names of these structures to envision how a specific variety might look.
As a longtime lover of bearded iris, Winton has many favorite varieties, including 'Fringe of Gold'. These varieties are also some of her favorites.
This variety is a dwarf tall bearded iris with yellow blooms. The petals have a white and deep purple-veined pattern that makes for a bold contrast on each flower.
White petals fade into light purple on the tips on this softer bearded iris variety. This mid-height selection also looks beautiful indoors in a vase where you can get a closer look at its multicolor petals.
'Perfect Pitch' is a true purple bearded iris that has ruffled petals. It's a tall variety, and it looks especially stunning planted alongside a few paler purple irises.
If you love purple, 'Ozark Dream' is the bearded iris for you. The top petals of the bloom are a light purple, while the falls are dark violet.
This tall bearded iris variety has a stark contrast between the top petals (which are white) and the falls (in a brick red hue). The red falls petals have a hint of magenta near the center, and the inside of the white petals has a light pink hue.