Japanese iris bloom time

Bearded, German, Japanese, Louisiana or Siberian: Irises are worldly perennials with more than 300 species

One of the oldest and best-known perennials in the home landscape is the bearded iris, sometimes called a German iris or a flag. But the genus Iris contains almost 300 species, and many irises have been hybridized extensively.

In the Greek language, the word “iris” means rainbow, which is fitting since the flowers come in a rainbow of colors. Irises have a rich history that dates to A.D. 500. They were brought to the New World by European settlers. Records show them in Virginia gardens as early as the 1600s.

Most species of iris are perennial plants but can be divided into two distinct types — those grown from a bulb, or “bulbous” irises, which include the Dutch iris and the reticulated iris; and those that grow from a rhizome, or “rhizomatous” irises. A rhizome is a modified stem that grows horizontally, sending out roots and shoots.

Of the rhizomatous types, there are three classifications — bearded, beardless and crested. Rhizomatous irises include the bearded or German iris, the Louisiana iris, Japanese iris, Siberian iris and the native woodland crested iris.

Iris plants are monocots, meaning their flower parts are in groups of three. In general, three sepals face downward and are referred to as “falls,” while the three upturned petals are called “standards.”

By far the most common iris grown in gardens is the bearded iris, Iris germanica. After a century of intense hybridization, they are often referred to now as bearded hybrids.

The name refers to the bushy “beards” that appear on the falls of the flower and help pollinators find the pollen.

According to the American Iris Society, there are six different groups of bearded irises based on size: miniature dwarf, dwarf, intermediate, miniature tall, border and tall. Their bloom times range from late winter to early summer. Some newer varieties bloom again in late summer or early fall and are known as “rebloomers.”

Gallery: The Irises

In Arkansas, the most popular bearded type is the tall bearded iris. Its flowers grow along bloomstalks 28 inches tall or taller.

The rhizomes are planted shallowly, with part of the rhizome exposed above ground — and no mulch should cover the rhizome. A spacing of 12-24 inches is best. They like a well-drained, light soil with at least 6-8 hours of sunlight a day.

If you have heavy soils, amend with organic matter. Fertilize with a complete fertilizer in the spring and again a month after bloom. Avoid putting the fertilizer directly on the rhizome.

A common problem can be the competition of grass and weeds. Make sure you clean the garden well before planting. Once established, bearded irises are very drought tolerant and relatively carefree — but you will need to lift and divide them eventually.

The rhizomes multiply horizontally and can form a mat over time. If they get too crowded they will stop blooming. They should be divided every three to five years, or sooner if their blooms begin to decline.

The best time to divide them is from mid-July to mid-August since the plants are usually dormant then. Since you plant iris rhizomes shallowly, you want to allow time for them to re-establish before cold weather hits.

You can thin a clump, leaving parts of the rhizome mass still in the ground; but digging up the whole clump and separating them is more common because the older rhizomes rot away leaving holes where mother plants once stood.

Some varieties are prone to diseases, and so many growers soak their divisions in a 10 percent bleach solution for 10 to 15 minutes, rinsing and then drying them before replanting.

Choose strong rhizomes with healthy fans to replant. Fans are the cluster of leaves that come from the rhizome. When dividing, you want to cut the fan back so it’s only 6 to 8 inches tall. Cutting helps sanitation, but it also prevents the wind from uprooting the shallowly planted iris until its roots re-establish.

Bearded irises typically bloom for two to five weeks, depending on the vigor of the plant. When planting, choose early, midseason and late-blooming varieties to extend the flower display in your garden.

A common question is whether it’s necessary to cut back the foliage after bloom. Unless you are dividing them, there is no reason to cut the leaves of bearded irises. Many growers do cut the leaves because they have hundreds (or thousands) of iris plants and want to provide better air circulation and sunlight penetration to reduce leaf-spotting diseases.

If you just have a few iris plants in your garden, there is no need to cut the foliage back.


While tall bearded irises are by far the most popular varieties here, there are several other irises that are great garden performers and will thrive in different locations.

Our native crested irises are much smaller plants that love the shade. In the wild they are typically found in deciduous forests in light to fairly heavy shade.

A wild crested iris only grows 6 inches tall, and the rhizomes are near the surface but typically covered with soil or leaf mulch. These little plants have lovely clusters of light blue or violet flowers that last two or three weeks in the spring. There are some white-blooming forms as well.

After bloom, the grass-like foliage can serve as a groundcover. Crested irises do best in a well-drained but rich site. They do not have to be divided unless you want to propagate them, and early fall is the best time to do so.


Beardless rhizomatous irises include the Louisiana, Japanese and Siberian iris plants. They do like full sun but they are planted in the soil, not at the soil level, and they need much more water than their bearded cousins.

Siberian irises like even moisture while Japanese irises like as much water as you can provide — but neither like to have wet feet in the winter.

Louisiana irises will grow in standing water year-round but will also do well in the ground as long as they don’t dry out.

Louisiana irises are native to Louisiana and the Gulf Coast. The wild copper iris is found in Arkansas, too, and like other Louisianas, likes swamps and moist areas. While that is where they grow in the wild, Louisiana irises also tolerate soil moisture conditions in a home garden. But they are not drought tolerant — they do need some supplemental watering in hot, dry summers.

They need 6-8 hours of sunlight a day but would like a little protection from the hot afternoon sun if possible.

Plant them 1 inch deep in organic soils. They will tolerate heavy clay soils, as they retain moisture well, but the addition of organic matter is helpful. Depending on the variety, mature plant size could be a foot to 6 feet tall, with flowers in a wide range of colors.

The purest red color available in an iris is found among the Louisiana irises.

Cut back the flower stalk after bloom. Clumps spread rapidly in good conditions, so space them several feet apart to give them room to grow.

Japanese irises (Iris ensata) and Siberian irises (Iris siberica) are similar in appearance, but the flowers are typically larger on Japanese irises, and the plants are 3 to 4 feet tall. Japanese iris foliage also has a very distinct raised central rib, which the Siberians do not.

Siberian irises grow 2-4 feet tall and bloom several weeks after bearded irises.

Japanese irises are the last irises to bloom and have the largest and showiest blooms. Japanese irises are planted 3 to 4 inches deep in rich soil.

For both types, keep the soil moist after planting and water if there is not plenty of rainfall, particularly until blooming ends. Both are heavy feeders and should be fertilized with a complete fertilizer in the spring and just before blooming. These plants have large sword-like leaves and can be difficult to transplant once planted. Give them full sun.

These are all great choices for the perennial garden.


The two bulbous irises are planted in the fall along with daffodils and tulips. The Dutch iris is not long-lived in our climate, but showy while it lasts. The reticulated iris is a tougher plant and blooms in early spring. They can colonize and come back each year.

Regardless of which iris you plant in your garden, or if you try them all, they can add much beauty to the landscape.

And if you want to learn more, consider joining an Arkansas iris society.

• In Little Rock, the Central Arkansas Iris Society meets at 2 p.m. on the third Sunday of the month in Hillcrest Hall, 1501 Kavanaugh Blvd. The April meeting conflicts with Easter, so they have moved that meeting to president Phyllis Kirtley’s home, 265 Woodridge Lane in Benton at 2 p.m. Sunday, April 28.

Their annual iris show will be May 4, with free admission from 1-4 p.m. at Grace Lutheran Church, 5124 Hillcrest Ave., Little Rock. For more information about the show or touring Kirtley’s Display Garden, call her at (501) 626-7258.

• The Hot Springs Iris Society meets at 2 p.m. on fourth Sundays except in April and December. They meet at Prince of Peace Lutheran Church, 109 Hobson Ave. in Hot Springs.

• The White County Iris Society meets at 2 p.m. on the first Sunday of every month except January, June, July and August, at 605 E. Race St. in Searcy. For information, call Alice Jewell at (501) 268-6634. Their iris show will be April 26 at Regions Bank in downtown Searcy. The rhizome sale is scheduled for June 29 at the downtown Searcy farmers market.

• The second annual Mountain View Iris Festival will be May 3 and 4 in the Courthouse Square in Mountain View. More information is at mountainviewirisfest.com.

The American Iris Society also has a website loaded with information about growing irises at irises.org.

Read Janet Carson’s blog at arkansasonline.com/planitjanet.

HomeStyle on 03/16/2019

Perhaps no other iris is as influenced by good culture as Japanese iris, properly known as Iris ensata. Demanding in their needs but if met they will reward you with tall robust plants and larger blooms. Hardy in zones 4-9.

Planting: Newly received plants that are bare root should be soaked in cool water for a few hours or overnight. Plant individual rhizomes 2-3 inches deep, 6 to 8 inches apart. Give a good 18 to 24 inch spacing between different named rhizomes. Water in well to start the root development, do not let new transplant dry out. Depending on your soils and weather a daily watering may be needed for the first week or two. Planting in a shallow depression will allow you to flood irrigate the plants. New transplants may not bloom the first year. Expect your best bloom on 2 and 3 year old plants.

This field has been tilled; the cow manure has been unloaded and will be worked in with a another tilling.

Caution: Do not use bone meal. This has the same effect as lime and can kill Japanese irises. Also, do not fertilize newly planted (or transplanted) Japanese iris as this can burn the roots.

Soil requirements: Japanese irises prefer a rich, loose soil with ample organic matter. An addition of well aged manure and compost will help in water retention as well as adding nutrients. The soil PH should be slightly acid, ideally between 5.5 to 6.5.

Japanese Iris can be among the largest of the iris. This three-year clump is ready for division.

Water: Japanese irises do not like to dry out. Constant moisture will reward you with healthy plants and larger blooms. Wet in the spring and keep moist all summer. They do very well near water (this is where they naturally grow) or where the water table is high. The crown of the plant needs to be above the water line.

Plant 2-3 inches deepWhen planting, create a shallow well or trough to keep water around your plants.Flood irrigate your plants for good soil to root contact.In as little as two years, these iris will provide a robust centerpiece for any garden.

Light: Full sun with a minimum of 6 hours to bloom properly. After noon shade in hot areas will benefit bloom.

Chad shows a pair of customers the root system of a ready-to-be divided iris.

Fertilizer: Japanese iris are heavy feeders. Depending on your soil a liberal application of balanced fertilizer for acid loving plants (Rhododendron, Camellia) in the spring just before or after bloom is beneficial. Most soils with heavy watering will usually need more nitrogen (Ammonium sulfate) applied. Do not apply fertilizers to new transplants.

Mulching: A mulch of 2 to 4 inches is recommended. This will keep the soil cool, retain moisture, and suppress weeds.

Transplanting: Japanese iris can be transplanted almost anytime from spring until fall if you keep the plant wet, and the temperatures are below 90 F and above 32 F for a month afterwards. Dig and divide your plants every 3 to 4 years to maintain plant vigor. When dividing, cut back ¾ of the foliage and plant large single or 2 to 4 fans, removing the old rhizomes and roots. Cooler maritime weather areas will find that transplanting right after bloom will get the plants back to bloom size for the following year. Plant 2 to 3 inches deep in new soils that have been worked up and amended. Your best bloom will be on 2 and 3 year old plants. Note: New roots form above the old roots each year forcing the crown up and out of the soil. It is critical to transplant every 3 to 4 years.

After digging out the iris… …invididual sections (or fans)… … are seperated from the larger plant.

Winter Dormancy: Remove and destroy old foliage with a serrated knife after a light frost, cutting the plants to the ground.

Pests: Slugs and snails; bait if damage is seen. Thrips and iris borer can be controlled with a systemic insecticide (i.e.: Merit or Orthene) following manufacturers’ instructions.

Old roots and rhyzomes are trimmed, then… … stalks are cut to about 6-8 inches. This is how plants are shipped, and customers receiving bare root iris should be sure to soak the plants in water a few hours before planting.

Caring for Japanese Iris

The care information provided in this section represents the kind of practical advice is available for all the plants in this web site if you subscribe to the monthly customized newsletter Yardener’s Advisor.
Cut off faded Japanese iris flowers to maintain an attractive look and stimulate new ones. Once the blooming period is over, cut off the old stems. Do not, however, cut the leaves back severely after flowering. The plants need their leaves for the rest of the season to store up energy for next year.
Watering Japanese Iris
Japanese irises require lots of moisture, about an inch a week. If they are in a regular garden bed, run a drip system when rainfall is sparse to keep the soil from drying out. Mulch the plants well. Near a pond where the water table is just below the soil surface, they can manage on their own. For information on products see the file on Choosing Watering Equipment
Fertilizing Japanese Iris
Japanese irises are heavy feeders and should be fertilized twice during the season. At planting time or every spring sprinkle a general purpose fertilizer formulated for acid-loving plants on the soil near the irises. Do not allow it to fall on the stems or leaves. Repeat this later in the summer just before they begin to bloom. As with other bulb plants, do not use manure.
Mulching and Weed Control
A 2 to 3 inch layer of chopped leaves, shredded bark or other attractive organic material spread on the soil over the iris rhizomes protects them. In the summer it discourages weeds and helps the soil retain moisture. In the winter it insulates the iris roots against the typical alternate freezing and thawing of winter. This minimizes soil heaving and disturbance of the shallowly planted rhizomes.
Propagating Japanese Iris
To acquire more Japanese iris plants and to keep existing ones blooming at their best, divide the broad clumps every 3 or 5 years. Do this either in the spring or early fall. Carefully dig up the knarled clumps of rhizomes and wash them off with the hose. Slice through their densely matted roots with a sharp axe or large knife, to make smaller chunks composed of 4 to 6 rhizomes each. Discard sections of older, weakened rhizomes from the center of the original clump. Replant the most vigorous ones as directed above. When dividing in the fall, trim back iris foliage for easier handling. Newly divided clumps of iris may not bloom the following season. With good soil conditions and an annual application of fertilizer, most clumps will bloom within a year or two.

Variegated Japanese Iris

Variegated Japanese Iris

(Photo courtesy of NetPS Plant Finder)

Variegated Japanese Iris foliage

Variegated Japanese Iris foliage

(Photo courtesy of NetPS Plant Finder)

Plant Height: 24 inches

Flower Height: 3 feet

Spacing: 18 inches


Hardiness Zone: 4b

Other Names: Japanese Water Iris, Russian Iris, Japanese Flag


Attractive variegated foliage and violet flowers; good for bogs or ponds, as it requires consistent moisture; blooms emerge from lush, sword-like foliage; hardy and easy to grow; cut back in the fall to reduce pests

Ornamental Features

Variegated Japanese Iris features showy violet flag-like flowers with yellow centers at the ends of the stems in mid summer. The flowers are excellent for cutting. Its attractive sword-like leaves remain green in color with showy white variegation throughout the season. The fruit is not ornamentally significant.

Landscape Attributes

Variegated Japanese Iris is an herbaceous perennial with tall flower stalks held atop a low mound of foliage. Its medium texture blends into the garden, but can always be balanced by a couple of finer or coarser plants for an effective composition.

This plant will require occasional maintenance and upkeep, and should be cut back in late fall in preparation for winter. Deer don’t particularly care for this plant and will usually leave it alone in favor of tastier treats. Gardeners should be aware of the following characteristic(s) that may warrant special consideration;

  • Insects

Variegated Japanese Iris is recommended for the following landscape applications;

  • Mass Planting
  • General Garden Use
  • Bog Gardens

Planting & Growing

Variegated Japanese Iris will grow to be about 24 inches tall at maturity extending to 3 feet tall with the flowers, with a spread of 24 inches. When grown in masses or used as a bedding plant, individual plants should be spaced approximately 18 inches apart. The flower stalks can be weak and so it may require staking in exposed sites or excessively rich soils. It grows at a medium rate, and under ideal conditions can be expected to live for approximately 10 years.

This plant does best in full sun to partial shade. It prefers to grow in moist to wet soil, and will even tolerate some standing water. It is not particular as to soil type or pH. It is somewhat tolerant of urban pollution. This is a selected variety of a species not originally from North America. It can be propagated by division; however, as a cultivated variety, be aware that it may be subject to certain restrictions or prohibitions on propagation.

Gertens Sizes and Prices

#1 container – $10.99
* Sizes and availability are subject to change. Please check with the store for specific details.

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