Transplanting iris in late summer

Tips For Bearded Irises Replanting And Dividing

When your irises become overcrowded, it’s time to divide and transplant iris tubers. Generally, iris plants are divided every three to five years. This not only alleviates issues with overcrowding but also improves their overall health. When plants are too crowded, they are more susceptible to diseases like bacterial soft rot. In addition, plants are less likely to produce any blooms. Keep reading to learn more about replanting bearded irises.

When & How to Divide Bearded Irises

The best time to divide irises is during late summer, usually anytime between July and the first of September. Carefully dig up your iris clumps with a spade shovel and gently lift each clump from the soil. Shake off the soil and rinse each rhizome with water.

Trim the existing foliage into a neat fan about a third of their overall

height, then use a sharp knife to cut or separate the rhizomes. In some cases, you may be able to just pull them apart. Make sure that each division or section contains a fan of leaves.

As you divide the rhizomes, take time to inspect them. Discard any that are old, leafless, soft, or rotting. Soft rot and iris borer are two of the most common causes for soft, mushy rhizomes in bearded irises. Replanting only the younger, healthier rhizomes will ensure the continual growth and vigor of your bearded iris plants.

Bearded Iris Transplant Instructions

Once you’ve ensured the health of your rhizomes through thorough inspection, you’re ready to transplant iris tubers. However, prior to transplanting irises, you’ll need to locate a similar area for replanting.

Bearded iris plants perform best in fertile, well-draining soil in areas with full sun. Their blooming is poor when given too much shade and poor draining can lead to bacterial soft rot.

Dig a hole large enough to accommodate at least three to five rhizomes. Mound the center with soil and place the rhizomes (with fans facing in one direction) on top, allowing the roots to sprawl over. Then fill in the hole and cover the rhizomes slightly—no more than an inch or just below the soil surface. Planting too deep can also encourage rotting.

Replant additional rhizomes the same way, spacing each group at least 12 to 24 inches apart. Water the irises thoroughly after transplanting. Newly planted irises should begin flowering within their second or third season.

Iris are beautiful when in bloom, and need to be divided regularly to remain healthy and bloom well.

Bearded iris are a great addition to the garden for their beautiful flowers in spring and their bold, vertical foliage. These plants need to be divided every few years, when flowering declines or the clump becomes crowded. This may occur in as little as 2 years or as many as 5. Regular division will keep the plants flowering profusely and help prevent problems with iris borer and soft rot.

Bearded iris can be divided any time after flowering; this is often done in July or August in the Midwest so the replanted portions will have plenty of time to develop new roots and become established before freezing weather arrives.

Lift clumps carefully to avoid damaging the rhizomes.

Lift clumps of iris carefully using a shovel or pitch fork. If the soil is dry, water the bed thoroughly a day or so beforehand to make digging easier. The heavy, but shallow-rooted rhizomes are generally easy to see, making it fairly easy to avoid injuring the rhizomes when digging. If possible, lift the entire clump as a whole rather than breaking it up. Shake off the loose soil from the clumps. If your garden soil is fairly loose, you should be able to get most of the soil off the roots, but you can rinse off any remaining soil with a garden hose if necessary.

Separate lifted rhizomes by pulling them apart.

Separate individual rhizomes by pulling apart tangled sections. Inspect the rhizomes carefully for signs of iris borer damage and soft spots from disease. (If the plants had dark streaks on the leaves, then the rhizomes likely are infested with borers. The female borer moth lays its eggs on the leaves in the fall, and the young caterpillars tunnel down the leaves to get to the rhizomes, leaving tell-tale streaks behind on the leaves. The plump, pink mature caterpillars generally leave the rhizomes in August to pupate in the soil.) Extract and kill any borers you find, and use a clean sharp knife or pruning shears to cut out any damaged parts. Disinfect the cutting tools between cuts to prevent the spread of disease. Also eliminate any older, spongy growth.

Trim leaves to reduce transpiration in the replanted sections.

Remove any damaged leaves, then cut the remaining leaves back to 4-6 inches long or 1/3 their original height. This not only makes it easier to work with the plant, but also helps reduce transpiration while the plant is becoming re-established. The leaves are often cut symmetrically on an angle, but there is no real requirement to cut them in a certain way.

Use a clean knife or pruning shears to cut the rhizomes apart. Make the cuts at natural divisions in the rhizomes, such as where it has forked. Make sure each piece is firm and light colored, at least 3″ long, has healthy roots, and has a fan of leaves on it. Trim any broken or torn roots (scissor work well for this).

Use a clean knife or shears to cut the rhizomes apart. Then trim any dead or damaged roots.

To help prevent infection, rhizomes can be soaked for about half an hour in a 10% bleach solution, if desired. They can also be treated with sulfur dust or an insecticide and/or fungicide if pest problems are severe – but this is usually not necessary. Soaked plants should be held in a shady place until dry.

Iris divisions ready for planting.

Allow the cut rhizomes to cure for a few hours or days – to allow the cuts to heal over – before replanting. The rhizomes can be stored in paper bags for a while, but survival is best when replanted soon after dividing.

Bearded iris should be grown in a sunny location with good drainage. If replanting in the same location, remove any debris and incorporate compost first. Space the divisions 12-18″ apart. Iris are often placed in groups of three divisions arranged in a triangle, with each fan of leaves pointing away from the other irises in the group.

To plant the rhizomes, prepare a shallow hole with a low mound in the center. You may add bone meal to the bottom of the hole, but since iris are not heavy feeders additional fertilizer is not needed in all soils. The rhizome should be placed horizontally on the mound, spreading the roots down the mound into the surrounding trench. The plant will grow from the end which has the fan of leaves, so point the rhizome accordingly in the direction you want it to grow. Then fill in the hole, leaving the top of the rhizome barely exposed or just covering it with no more than an inch of soil.

Place the rhizomes shallowly on a mound in the planting hole (L) and just cover the rhizome (R).

Bearded iris in bloom.

Bearded iris is susceptible to root rot if buried too deeply. Tamp down the soil and water thoroughly after planting. Keep the soil moist but not wet until new foliar growth occurs. Newly planted iris should be mulched their first winter (after the ground freezes) to prevent damage to the rhizomes from alternate freezing and thawing. Remove the mulch in early spring. Transplanted iris will only bloom sparsely the first spring after replanting.

– Susan Mahr, University of Wisconsin – Madison


Download Article as PDF

By Julie Christensen

Like lilacs, bearded irises have been around for a long time. These classic garden plants, sometimes known as “flags,” deserve a place in every garden. They produce beautiful blooms from spring to mid-summer and take almost no maintenance.

Bearded irises (Iris germanica) grow almost everywhere in the U.S. Hardy in USDA zones 3 through 9, they need at least a bit of frost during the winter to break dormancy in the spring. Bearded irises aren’t bulb plants, but they form from tubers, or soft, fleshy roots. Note that care is different for beardless irises, so be sure you know which kind you have.

Planting and Growing Bearded Iris

Bearded iris grows and blooms best in a location that gets at least six to eight hours of sunlight every day. In hot climates, a location with afternoon shade can work well. Plant bearded irises from late summer to early fall. Plant them at least six weeks before the first fall frost though so roots become well established.

When planting bearded irises, inspect the tubers first, and throw away any that are soft, dark or mushy. An off-odor can also indicate rot or disease. Irises aren’t particular about soil, although it must be well-draining. They grow best in light, loamy soil with a pH near neutral, although they’ll tolerate slightly acidic and alkaline soils.

Irises need good air circulation so plant them at least 18 to 24 inches apart. Plant the tubers so they sit just at soil level. In hot climates, you can plant them slightly deeper, but planting them too deeply will encourage lots of vegetative growth and few flowers. Water the soil frequently immediately after planting as the roots become established.

Once the roots are established, reduce watering to once or twice per week, or just enough to keep the soil moist 3 inches beneath the surface. Overwatering is a leading cause of iris failure and promotes root rot diseases. Mulch, usually a good idea in the garden, is discouraged for irises because it keeps the soil moist.

Fertilize irises in spring and again after blooming with a low-nitrogen formula, such as 5-10-10, at a rate of 2 tablespoons per plant. Remove the spent flowers too. Allowing them to go to seed or form seedheads saps energy, reducing the blooms you’ll see in coming years.

Dividing Irises

Like many rhizome-forming plants, irises need regular division to remain vigorous. After three or four years, the main rhizomes wither and die. Newer side shoots form, but the main plant starts to decline. The plants may also become overcrowded and more prone to disease. By dividing irises every three to four years, your irises will remain healthy for years to come.

Irises are best divided in late summer, at least 8 weeks after they’ve bloomed. To divide irises, use a spade or garden fork to carefully lift them out of the soil. Try not to spear or cut the rhizomes. Cut the foliage back to 4 to 6 inches. This pruning might seem harsh, but it reduces transplant shock. The old iris rhizome will have many young rhizomes attached to it and each one will have its own set of leaves. Break off each of these young rhizomes, using your hands or a knife if needed.

Once the rhizomes are divided, examine each one. Young, healthy iris rhizomes are about ½ inch wide. They should be firm and have several leaves emerging from them. Discard those that are old and thick, especially if they have no top growth. Also discard those that are shrunken, shriveled or soft. Some gardeners wipe the rhizomes with a solution of 1 part chlorine bleach to 10 parts water to prevent disease problems. This strategy isn’t necessary in dry climates, but might be a good idea in a warm, humid area. Of course, it only works with rhizomes that are healthy to begin with.

Replant the healthy irises, spacing them 18 to 24 inches apart. Remember to plant them shallowly so the tops of the rhizomes are barely covered with earth.

For more information on growing and dividing bearded irises, visit the following links:

Dividing Irises

How to Plant and Grow Bearded Iris from the American Iris Society

Bearded Iris for the Home Landscape from North Carolina State University Extension

Julie Christensen learned about gardening on her grandfather’s farm and mother’s vegetable garden in southern Idaho. Today, she lives and gardens on the high plains of Colorado. When she’s not digging in the dirt, Julie writes about food, education, parenting and gardening.

How do I divide and transplant Bearded Iris?

Iris need to be thinned or divided before they become overcrowded, generally every 3-5 years. If Iris are allowed to become too crowded the bloom will suffer, some varieties may crowd others out and disease problems may be aggravated. Depending on your location, July through September is the time to divide and transplant Bearded Iris.

Transplanted Iris should be planted a minimum of six weeks before the first hard frost in your area.

Old clumps may be thinned by carefully cutting out the old divisions at the centers of the clumps and leaving new growth in the ground. In the case of very old and compacted clumps, the process of thinning might be easier if you dig up the entire clump, remove the old “spent” rhizomes, trim the foliage of the new rhizomes and replant them. Smaller shoots may take two years to produce blooms, but larger shoots should bloom the following spring.

We recommend supplementing the soil with a low-nitrogen fertilizer, super phosphate or bone meal when transplanting. These extra nutrients help the new shoots to have the best chance of success in establishing their root systems. Water newly planted rhizomes well initially, and if dry conditions continue then once every 7 to 10 days until the autumn rains begin, to help the new roots become established.

Is your Iris bed overgrown? Need saving? Read our blog post at WordPress for more tips and reassurance….

Watch Ben Schreiner’s short tutorial on how to dig and divide bearded iris:

Dividing Perennials in the Fall

General Dividing Tips for Perennials

Water really well, 1-2 days before dividing. Cut foliage back to 6” or half the plant to make it easier to cut.

Reasons Why We Divide Perennials

  1. Flower production is reduced
  2. Smaller flower heads
  3. Center of plant dies out
  4. Plant loses vigor
  5. Plant flops and now needs staking
  6. Plant has outgrown its bounds

3 Goals when Dividing Perennials

  1. Rejuvenating the plant so it can continue to perform the way it was intended
  2. Control the size of the plant
  3. Increase the number of plants

Plants to divide in late summer to fall:

  • Beebalm
  • Campanula
  • Cranesbill (Geranium – perennial)
  • Black Eyed Susan
  • Garden Phlox
  • Hosta
  • Daylilies
  • Iris
  • Peony
  • Poppy
  • Yarrow
  • Coreopsis
  • Coneflower
  • Yucca

Dividing Daylilies

Fall is a good time to thin and transplant crowded clumps. Separate and cut foliage back by 50%. Replant.

Be sure to water your plants extra in the days before you divide, they will need the strength to be transplanted successfully.

Dividing Hosta

After flowers have faded, dig up your hosta and wash away the soil from the roots. You’ll see lavender eyes that will become next year’s plant. Take a sharp knife and cut to one side of those eyes. Replant.

Planting & Transplanting Iris

The Greek goddess Iris walked a rainbow pathway through the sky and the flower named for her has a rainbow of flower color. This radiant flower was regarded as the symbol of light and is emblematic of promise, light and hope, pride and bravery.

The best time to plant and transplant Rhizomatous Iris is late July through September. Rhizomes are horizontally growing underground stems that are used as food storage for the plants. Rhizomatous Irises include the common bearded Iris as well as the beardless Siberian and Japanese Iris.

Iris love the heat and the drier wether of summer, and summer dividing will reduce the incidence of bacterial soft rot. Most Iris need to be divided every three to five years. If your plants are not producing many flowers, it’s time to DIVIDE and CONQUER!

Steps for dividing iris:

  • Cut back the foliage to about one-third its height.
  • Lift the entire clump with a spade.
  • Use a sharp knife to separate the rhizomes. Dip the knife in a ten percent bleach water mixture after each cut.
  • While dividing, make sure to inspect the rhizomes for soft rot and iris borer. Iris borer is the worst insect problem that can affect Iris. An Iris borer adult is a brownish moth and she lays her eggs in fall on iris leaves, which over winter there and hatch into caterpillars during April and May. The caterpillars first bore into the Iris leaves and by the end of July, the caterpillars move into the rhizome to eat and mature. In early August, the caterpillars move from the soil to pupate into a moth.
  • When dividing, the Iris borer will be a mature pink caterpillar inside the rhizome and it will be mushy to the touch. Bacterial soft rot often accompanies iris borer damage. If there is evidence of Iris borer, spray with Cygon the following spring.
  • To avoid any decay on the new breaks or cuts, dust the rhizomes with a powdered fungicide such as sulfur or Bulb Dust.
  • The new transplants should have a firm rhizome with roots and a fan of leaves.
  • Remove and discard the old rhizomes and replant the younger smaller rhizomes that grow off the older stems.
  • Replant in a sunny, well-drained garden spot. Dig the hole about 5 inches deep and build a small mound in the middle to place the rhizome.
  • Place the rhizome on the mound allowing the roots to fall down either side and cover the roots so that the rhizome is ever so slightly exposed. Do not plant rhizomes too deep or it may rot or not flower.
  • As a rule of thumb, Iris are planted 18-24” apart in groups of three to seven sections of one variety.
  • Typically the rhizomes are planted so the leaf fans face in one direction.
  • Fall sanitation is very important in the control of Iris borer. After the first hard frost, remove and destroy the old iris foliage and plant debris to remove any eggs.
  • Keep well watered, but not too wet.
  • Cover after the ground has frozen if you are dividing.

Leave a Reply

Your email address will not be published. Required fields are marked *