How to Grow and Care for Bearded Iris

How to Plant Bearded Iris

When to Plant

If planted from nursery starts, the bearded iris is usually planted in the spring and will flower in its first year. If planted from bare roots, it can be planted in the fall or the spring; bare-root plants may not flower robustly until their second year. Bearded irises have a moderate growth rate, with the capacity to grow 4 inches to 40 inches in one year.

Selecting a Planting Site

Bearded irises need full sun to grow. The best growing conditions for them include a site with well-draining soil that cannot tolerate clay-like soils. In the hottest climates, the full sun might become too harsh for longer than six hours, so ensure it has some shade cover for a portion of the day. They can tolerate all-day sun in cooler climates, such as in the lower USDA zones 4 and 5.

Spacing, Depth, and Support

Plant the rhizome rooting structures about 1 to 2 feet apart. They do not need to be planted too deep. Most rhizomes should be planted below the surface, exposing the top with any roots pointed downward. However, in a hot weather climate, at the upper range of USDA zones 7-9, consider covering the top of the rhizome with 1 inch of soil. After planting, lightly water to settle the soil around the root structure.

Tall bearded irises will likely require staking, especially during high winds or inclement weather. Use a long bamboo stake planted close to the base, but avoid harming the rhizome when digging it into the ground.

Bearded Iris Care Requirements

The most popular of the irises, bearded irises are easy to grow provided you plant them in a sunny site with well-drained soil. A major departure for growing irises compared to other perennials is that they do not like mulch. Mulches (as well as deep planting) encourage the rhizomes to develop rot, so let your soil remain bare. Space plants at least 12 inches apart to prevent the need for frequent dividing.

Here are the main care requirements for growing bearded irises:

• Plant in a sunny location.
• Ensure it has well-draining soil.
• Do not layer the top of the soil with mulch (in most zones).
• Only water when the top two inches of soil are dry.
• Give low-nitrogen fertilizer in the spring to encourage bloom.

Sun Requirements

Irises need full sun to thrive. In full shade, they produce fewer blooms and may suffer from an increase in diseases.

Soil

Heavy clay soils do not work well for growing iris, but sandy or gravelly soils are excellent. If your native soil is heavy, you can plant irises in raised beds to help drainage. To lighten the soil, you may also amend your soil with gypsum or organic matter like compost.

Water

Although irises like moisture, they also need good drainage to prevent rot. Water them when the top 2 inches of the soil feel dry. These plants have a good drought tolerance.

Temperature and Humidity

Irises are notorious for their hardy disposition. They don’t mind temperature extremes if the soil allows excess rain or snowmelt to drain away. Irises damaged by heavy winds or hail can be susceptible to iris borer larvae.

Fertilizer

In the spring, apply a low-nitrogen 6-10-10 fertilizer around your irises. Too much nitrogen will encourage foliage at the expense of blooms. Bone meal is also a good fertilizer.

Types of Bearded Iris

Iris groups are categorized as “bearded,” “beardless,” and “crested.” Japanese, Dutch, and Siberian iris are among those that fall into the beardless category.

Within the broad category of the popular bearded iris group, there are also subcategories: tall bearded, intermediate bearded, short bearded, miniature bearded, and border bearded. The main distinguishing feature of these subcategories is their stature, although they also vary somewhat in bloom time. Most irises bloom in the spring, and some varieties can rebloom in the summer or fall.

New named varieties of bearded iris are developed for commercial sale every year, and the ranking of the most popular irises, conducted annually by the American Iris Society, changes frequently. When looking for irises to plant, it’s a good idea to look for those that have won well-known awards, such as the Dykes Medal. There are many dozens of fine irises to choose from; here are some award-winners that are widely grown:

• “Celebration Song” is a tall, pink, or lavender bearded iris growing to 37 inches.
• “Abiqua Falls” is a true blue tall bearded iris that grows to 39 inches.
• “Again and Again” is a yellow, reblooming, tall bearded iris growing to 36 inches.
• “American Classic” is a white with blue-violet iris, a tall beard that grows to 36 inches.
• “Beatnick” is a dwarf bearded iris that grows to 14 inches. Its purple flowers have white highlights.
• “Big Blue Eyes” is a dwarf bearded iris with white and violet flowers. It grows to 14 inches.
• “Dusky Challenger” is a dark purple iris, growing to 39 inches tall.
• “Thornbird” is a beautiful yellow iris that grows to 37 inches.
• “Queen’s Circle” has white flowers with blue-lavender fringes. This iris grows to 32 inches.
• “That’s All Folks” is a towering 40-inch yellow-gold iris.
• “Jesse’s Song” is a 35-inch tall violet and white iris.

Pruning

Faded, withered flowers should be pinched off immediately. Pruning may promote additional blooms or even a repeat bloom period later in the season.

Every four or five years, clumps of iris should be dug up, divided, and replanted to cull out diseased roots and iris borer damage. Dividing will keep iris plants vigorous and allow you to propagate new plants.

Propagating Bearded Iris

Dividing irises will multiply your iris plants for your garden. Division of the rhizome keeps existing irises healthy. Here’s how to divide irises:

1. Dig up the rhizomes with a shovel in late summer and shake off all loose soil. Any flower stalks that are still in place can be removed at this time.
2. Carefully pull or cut the rhizome cluster apart into sections. Make sure each section has a fan of foliage; you can trim the foliage off at an angle, leaving 3 to 6 inches of leaves intact.
3. Examine the root sections closely, and use pruners to cut away any soft, rotten parts. Make sure to cut the roots back past any borer tunnels—you may even encounter living worms, which should be destroyed.
4. Replant each root section, just barely covering the rhizome. Space roots at least 12 inches apart will quickly fill the spaces. Water thoroughly upon planting, then weekly until frost sets in. New foliage growth will probably begin in late summer and fall, and the plant will grow vigorously when it returns in the spring.

Divide irises every three to five years—or more often if iris borers have infiltrated the plants.

How to Grow Bearded Iris From Seed

Propagation by seed is generally only done by nursery professionals when they seek to breed new varieties by careful cross-pollination. However, it is possible to grow iris from the tiny seeds in the green oval pods left behind after the flowers fade. If you collect the seeds and plant them about 14-inch deep in the garden, they often will sprout and mature into flowering plants within three years.

But be aware that most garden iris are hybrids, and plants propagated from their seeds usually do not “come true.” The iris plants you propagate by collecting seeds may look quite different from the mother plant.

Propagation is almost always done by dividing root clumps—a speedier and more reliable method.

Potting and Repotting Bearded Iris

Although it’s not a common method, you can grow irises in pots at least 12 inches wide. Use a loose, soil-free potting mix, and leave the tops of the rhizomes exposed or just barely covered. Do not overwater the plants.

In colder climates, you may need to move the containers to sheltered locations for the winter to ensure the plant’s’ survival. Irises in containers may need dividing and transplanting more frequently than those growing in the ground—about every other year.

Overwintering

Trimming back foliage fans to about 6 inches in the fall makes the garden look tidy, reduces leaf surface area that might host fungal disease, and removes caterpillar eggs. Destroy all foliage you remove, and do not add it to the compost bin.

If plants show signs of rot or damage from borers, the roots should be dug up and inspected in early fall. Cut away any diseased or worm-damaged sections and replant the remaining root sections. Ideally, this should be done several weeks before freezing weather sets in to allow the roots to reestablish before frost.

Common Pests and Diseases

Though irises do not suffer many problems, routine lifting and dividing are necessary to combat iris borer worms and keep plants healthy and productive.

The iris borer is the most serious insect pest of irises. In the spring, caterpillars hatch and tunnel through leaves, reaching the rhizome by summer. Feeding tunnels allow the rhizome to become infected with bacterial rot, compounding the damage. Remove all iris leaves after frost to remove caterpillar eggs, as well. Where worms penetrate rhizomes, dig them up, cut away soft, infested portions, and replant the pieces.

Major disease problems include bacterial soft rot, crown rot fungus, and fungal leaf spot. The mottling of leaves and flowers suggests the presence of the mosaic virus. Affected plant material should be removed and destroyed (not placed in compost). Good hygiene is usually enough to control these diseases; fungicides aren’t usually needed.

How to Get Bearded Iris to Bloom

Bloom Months

Bearded iris typically blooms in April or May. Some reblooming cultivars may rebloom in summer or fall.

What Do Bearded Iris Flowers Look and Smell Like?

Bearded iris flowers are best known for their large, ostentatious flowers. They have six petals—three upright standard petals and three floppy petals that fall downward. The petals have a central, bearded line leading inward to the flower center.

Of the irises, bearded irises are the most fragrant. Some cultivars are more fragrant, with scents ranging from orange blossom to grape soda.

How to Encourage More Blooms

• Proper planting depth: Don’t plant the rhizomes too deeply. When replanting divisions, ensure the rhizome crown is barely covered with soil.
• Give ample sun: Ensure the iris gets at least six hours of direct sunlight daily.
• Do not overfeed: Too much fertilizer causes the iris to put energy into leaf growth at the expense of flowers. All it needs is a single feeding in the spring.
• Divide every few years: Flowering will fall off radically when root clumps become too dense. Dig up your irises every few years to divide and replant them.

Common Problems With Bearded Iris

Of the irises, the bearded iris is arguably the most popular and is among the easiest to grow. Bearded irises are largely trouble-free but can develop a few issues.

Leaves Turn Yellow or Brown, Fall Over

Yellowing and browning can be a sign of root rot caused by excessively wet soil or extensive damage from iris borers. It is best to immediately lift affected root clumps, cut away any soft, decaying areas, and replant in porous and well-draining soil.

Flower Stalks Topple Over

Some bearded irises grow as much as 40 inches tall, and staking may be required to support the huge flowers. Irises that grow in shady conditions may get even leggier, making staking a necessity.

Leaves Have Yellow and Brown Spots

Spotted leaves are the result of bacteria or fungal infections. Bacterial leaf spot usually begins on the edges of the leaves, gradually enlarging. Fungal leaf spots typically appear on the inner part of the leaves, and they do not enlarge in size. Affected plant parts should be removed and destroyed. Keep the ground around the irises free of mulch and debris. Good garden hygiene usually controls leaf spot diseases. Serious fungal infections can be controlled with fungicides.