Iris Classification – Beardless Irises

The following is derived from information on The American Iris Society (AIS) website at The AIS divides irises most often used as garden plants into three main groups: Bearded Irises, Aril Irises and Beardless Irises.

Beardless Irises normally bloom after Tall Bearded Iris (except for the Pacific Coast Native which blooms before the TBs). There are 6 types of irises classified as Beardless Iris: Spurias, Siberians, Japanese, Louisianas, Pacific Coast Natives and Species. Because the majority of these bloom after the TBs, they often extend the iris season in the garden.

1. Spurias (SPU) are between 2 and 5 feet tall and very elegant-looking. The bloom shape is often like an orchid. Spurias come in many colors and often have a bright yellow signal.


2. Siberians (SIB) come in multiple colors: blue, purple, red-violet, yellow, brown and orange. They prefer cooler temperatures, moisture and like a slightly acidic soil. Their blooms can be upright or round and flat. They look best when grown in clumps at a height of 2 to 4 feet. They usually bloom right after the TBs and their grass-like foliage is an attractive garden feature.

3. Japanese (JI) iris also prefer slightly acidic soil. Their blooms are gorgeous – huge, ruffled and flat. Japanese bloom about a month after TBs.

4. Louisianas (LA) are native to the U.S. Gulf Coast area. They perform best in somewhat acid soil and prefer to be wet in the spring. Blooms have brightly colored style-arms and also signal-crests; they are usually wide open.

Iris 'Black Gamecock', Louisiana Iris, Purple Iris, Purple flowers, Dark Flowers, Dark Iris

5. Pacific Coast Natives (PCN) are normally grown in the far western part of the U.S only due to climatic conditions. They are usually one to two feet tall and are graceful, dainty flowers.

6. Species iris have 2 classifications: I. confusa and I. missouriensis. The latter prefer wet springs and dry summers; we often refer to them as Blue Flag or Rocky Mountain iris. The former want conditions similar to azaleas in a frost free climate.

Iris missouriensis - Wikipedia

Iris Classification – Aril Irises

The following is derived from information on The American Iris Society (AIS) website at The AIS divides irises most often used as garden plants into three main groups: Bearded Irises, Aril Irises and Beardless Irises.

Aril irises include oncocyclus and regelia irises of the Near East. Both types have beards; however, they are not classified as bearded irises, their beards are sparse. Beards on regelias are long and straggly. Beards on oncocyclus are more like a “fuzzy” patch. Arils have a dark spot below the beards, called signal spots, there is a lot of veining and speckling in a large range of colors.

Arils are normally found in only the warmest and driest regions of the U.S. A hybrid called arilbred was produced by crossing arils with bearded irises. Arilbreds are easier to grow here and still have the features of an aril. Most are tall with large blooms that bloom with the SDBs and the IBs (earlier than TBs).

Smaller arilbreds have also been produced by crossing arils or arilbreds with dwarf or median bearded irises.


Digging, Dividing & Replanting Tall Bearded Iris

By Carrie Winter

So your tall bearded irises simply did not bloom well this year, despite having produced many bloom in previous years . . . What’s the problem?  If the clumps have been in place three or more years, it’s time to dig, divide and replant.

The ideal time to dig is when the rhizome (actually an enlarged stem, but often called bulb, tuber or root by non-Master Gardeners) is fully mature and on the brink of summer dormancy.  That time for the Charlotte, NC, area is July, not the most pleasant time for digging in the garden.  However, since the rhizomes are growing near the soil surface, a clump is really quite easy to dig with a garden fork or shovel.  Simply slide the fork or shovel under the clump, raise it up, and place the clump in a tub or on a plastic sheet.  If you are digging more than one variety, it is important to keep them separate and properly labeled.

Remove the soil from the rhizomes and, with your hands or a knife, separate the clump into individual rhizomes with a fan of foliage.  Examine each of the fans or divisions carefully for evidence of disease, especially rot.  Discard these and the “mother” rhizome of the clump, saving all the young and healthy rhizomes.  Trim the foliage of the fans to be saved into an inverted vee about six inches high.

At this point, the trimmed rhizomes can be washed, drained and dipped into a solution of 9 parts water to 1 part bleach, rinsed and drained again.  The rhizomes should then be allowed to dry in shade that is open and dry.  Most home gardeners generally omit the washing and rinsing steps.  Rhizomes may be left out of the ground for up to several weeks, if necessary.

Now you are ready to replant.  Before the dig or while the rhizomes have been drying out, the replanting area should be prepared.  Your site should be well drained and receive at least six hours of full sun for maximum bloom.  Dig the area to a depth of 10-12 inches and add soil conditioner, low nitrogen fertilizer and a dash of superphosphate.  Lime is typically a useful and often necessary additive to Mecklenburg County clay to achieve a pH of 6.1-7.2.  Work in the additives carefully so that none of the fertilizers will rest on the rhizomes.

The rhizomes of tall bearded iris should be placed 12-18 inches apart.  If you have 3 rhizomes of the same variety, you may want to plant them in a triangle to achieve an immediate clump effect.  The toe of each of the rhizomes should point to the center of the triangle.  Each rhizome should be planted horizontally on a slight ridge so that the roots can spread out on both sides of the ridge.  Cover the rhizome while leaving the upper surface of the rhizome exposed to the sun.  Secure the roots in the soil and water well for the first week or two while a good root system develops.  After that time, watering of bearded irises in the Charlotte, NC area should not be necessary, making them an ideal plant for water conservation during our hot, dry summers. 

AIS Webinars

  • The American Iris Society (AIS) hosts webinars relating to iris.  View video recordings of these webinars on YouTube.  Topics include:
    • Growing Iris Basics
    • Novelty Iris
    • Louisiana Iris
    • Managing Pests and Weeds
  • To access these YouTube recordings:


Recommended Care for Bearded Iris Throughout the Year

Take advantage of any warmer days to care for your bearded iris.  Tree leaves are all down and they must be removed to prevent pests and disease.  Remove any totally brown iris foliage but do NOT remove green foliage and NEVER cut foliage in a fan shape in the garden.  The plants need their leaves to promote growth.  The top of the iris rhizome wants to bask in the sun.  If weeds are a problem, Preen or another pre-emergence can be applied.

Pre-spring is a good time to apply super phosphate or triple super phosphate.  As it contains no nitrogen, it is slow acting, but promotes bigger and better blooms.  Avoid getting granules on the rhizomes.  TB irises require soil of pH 6.8 to 7.2.  Lime reduces the acidity in our clay soil.  Get your soil tested to accurately determine the pH.  This also a good time to check identity labels as some may have faded or been displaced by animals such as deer.  A good practice is to put the iris’ name on the underneath side of the label as well.

Intermediate irises (MDBs, SDBs, IBs and MTBs) are sequentially sending up their bloom stalks.  Early and reblooming tall bearded irises are also beginning to show growth.  Continue with leaf cleanup.  Survey for garden for space to add new irises.  Check catalogues and/or on-line growers’ listings.

While you are enjoying your garden of irises, be on the lookout for evidence of borer infestation.  The tiny larval stage of a night flying moth starts at the top of the iris fan and chews its way down the plant leaving a slimy hidden trail.  Check carefully and eradicate by squashing the invader of use a systemic insecticide-labeled specifically for the iris borer.  If not dealt with, the borer continues its feast into the rhizome and can cause rot.  If leaf spot is evident spray with a fungicide that is used for leaf spot of roses.  Remove spent blossoms and keep beds clean.  The last Saturday in April is traditionally the date of the annual iris show.  Check your rises regularly for potential specimens in anticipation.  Stake a way-ward stalk if required.  Enter your iris stalks and enjoy the show.

Later blooming irises will still be lighting up your garden with color.  Re-blooming TB irises need a light application of fertilizer and require water if rains aren’t enough.  Remove spent bloom stalks by pushing the stalk inward toward the center of the clump and it will snap-off at ground level.  Monitor for rot if too rainy.  If you grow Siberian irises, they will be in their prime bloom season.

Continue monitoring for borers and clean-up as well.  Don’t allow foliage from other fast-growing perennials to encroach on the iris plantings.  This is a good time to order new iris rhizomes.  A great source for selecting the best and latest “tried and true” introductions is the AIS bulletins.  You will find the current winners and invaluable TB Symposium Popularity Poll listings.  Check on-line for listing of the Dykes Medal winners.  You will also find the advertiser’s section very helpful for ordering.  If you are not already a member of the American Iris Society, consider joining.  You will receive quarterly bulletins that contain full color photographs with many informative articles.  Contact for more information.

Evaluate for replanting and division of rhizomes.  Tall bearded iris should be divided every three or four years.  If crickets are present and eating holes in rhizomes, cover the rhizome temporarily with creek sand.  The Charlotte Iris Society holds its annual rhizome sale in July or August.  Dig and prepare rhizomes to contribute to the sale.  (This is when the foliage is cut in a fan shape on the dug rhizomes and plants disinfected with a 10% solution of Clorox, the rinsed and dried).  Prepare new beds for irises.  Remember to check the pH (6.8 to 7.2) and adjust with lime as necessary.  Consider making raised beds.  Potted irises can benefit from alfalfa pellets and bone meal, bedded irises as well.

Continue planting, remember “good planting rules” with the rhizome’s top exposed to the sun.  Monitor for borers and water plants as needed.

This is that exciting time when orders placed earlier will be coming to your mail box.  Make permanent labels (CIS sells them) and diagram the plantings for identification in the event a label is misplaced or lost to animal damage.  Nothing is more disheartening than to have lovely bloom stalks and no idea of its identity.

In this NC area, we can still plant irises.  Squirrels like to dig to hide acorns in newly dug areas, so check that they haven’t dug your plants as well.  Fertilize again with a low nitrogen fertilizer, such as 5-10-10.  Remove any totally browned foliage.

If you must still be planting, place a rock or brick on the rhizome temporarily to prevent it from heaving in freezing and thawing during the winter.  Continue to enjoy re-blooming stalks.  Be judicious in removing falling leaves from the plantings.

Enjoy the holidays!  Remember, gardening is a compromise with the weather, work when you can.  Gardening is therapy mixed with a full dose of passion.  Happy New Year!