By: Nikki Tilley, Author of The Bulb-o-licious Garden
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 (2.5 cm.) 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 (30-60 cm.) apart. Water the irises thoroughly after transplanting. Newly planted irises should begin flowering within their second or third season.
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How to Divide Bearded Iris Plants
Bearded irises are tall, elegant additions to the flower border, but they are also relatively high maintenance. You can help cut down on the incidence of soft rot and borer damage through regular division of the iris rhizomes every two to three years. This will also keep bearded irises performing and blooming at their best. If left undivided, flowering will decrease and the rhizome will be subject to more pests and damage.
Transplanting Irises - How To Divide Bearded Irises To Transplant - garden
Originally Published by Sandra Mason on 7/22/2000
The Greek goddess Iris walked a rainbow pathway through the sky and the flower named for her has a rainbow of flower colors. Iris is one of the oldest garden flowers. Iris is often seen as the only remnant of a long since abandoned home.
Although the most familiar type of iris is the bearded iris, the genus includes 200 or more species including some North American natives. Species are separated into two major groups - rhizomatous and bulbous. Rhizomes are horizontally growing underground stems that are used as food storage for the plant. The common bearded iris falls into this group as well as the beardless Siberian and Japanese iris.
Bulbous irises form a more typical bulb and include Dutch and reticulate iris. These are planted in October with other bulbs.
The best time to plant and transplant rhizomatous iris is late July through September. Iris loves the heat and drier weather of summer and the summer dividing will reduce the incidence of bacterial soft rot. Most rhizomatous iris should be divided every three to five years. If your iris patch is producing very few flowers, it's time to divide and conquer.
When transplanting iris, first cut back the leaves to about one third of their height. Lift the entire clump with a spade or digging fork. Use a sharp knife to separate the rhizomes. Dip the knife in ten percent bleach after each cut. The new transplants should have a firm rhizome with roots and a fan of leaves. Remove and discard the old rhizomes and only replant the younger smaller rhizomes that grow off of the older stems.
Iris appreciates a sunny well-drained garden spot. When planting iris, dig a hole about five inches deep. Build a small mound in the middle of the hole. Place the rhizome firmly on top of the mound and let the roots fall down the mound. Cover the roots with soil so the rhizome is just slightly exposed. Do not plant the rhizome too deep or it may rot. Generally iris are planted 18-24 inches apart in groups of three to seven sections of one variety. Usually the rhizomes are planted so the leaf fans face in one direction.
While dividing the rhizomes be sure to inspect them for soft rot and iris borer. Iris borer is the worst insect problem irises ever get. The adult iris borer is a brownish moth. She lays her eggs in fall on the iris leaves. The eggs overwinter and hatch into caterpillars during April and May. The caterpillars first bore into the iris leaves. By the end of July the caterpillars move into the rhizomes to eat and mature. In early August the caterpillars move from the rhizome to the soil to pupate into a moth.
When dividing iris, the iris borer will be a mature pink caterpillar inside the rhizome. The rhizome may look fine until your fingers push through to a mushy mess. Bacterial soft rot often accompanies iris borer damage.
Fall sanitation is important in iris borer control. After the first hard frost, remove and destroy or bury the old iris leaves and plant debris to remove the eggs. In small iris patches the borer can also be controlled by squishing the caterpillar in the leaves in April and May.
With so many colors and types of iris available including rebloomers, include a few in your garden plan.
If you find you just have way too much produce, why not donate it to "Plant a Row for the Hungry." Drop off your extra produce at Schnuck's Grocery Stores in Champaign or Urbana each Saturday from 10am–1pm starting July 22. All produce goes to the Eastern Illinois Foodbank.
How to Replant Iris
The elegant bearded iris (Iris germanica) is an old-fashioned garden staple featuring swordlike foliage and large, distinctive blooms with three petals upright and three down-turned falls. One reason for the plant's ubiquitous presence is its ability to spread, leaving gardeners with divisions to replant or pass along every year or two to keep plants blooming vigorously each spring. The plant grows from fleshy rhizomes just below the surface of the soil and has slightly different planting requirements than other perennials. It thrives in USDA hardiness zones 3 to 10.
Turn over the soil with a shovel to a depth of 10 inches in a site that receives at least six hours of sun per day with soil that drains well. Begin preparing the site several weeks in advance of lifting your iris rhizomes, advises Dorothy M. Downing, Master Gardener of University of California Tulare/Kings Counties.
Spread a layer of compost and a sprinkling of bone meal over the site and work it into the soil.
Pop iris clumps out of the ground any time from a month after they have finished blooming to fall when the soil begins to cool. They are shallow-rooted plants, growing on horizontal, fleshy rhizomes just below the surface, easy to lift with a shovel or garden fork.
Rinse the rhizomes off with a hose to make it easier to see the joints in the rhizomes.
Cut the rhizomes into pieces a few inches long, each with one fan of leaves attached.
Trim the leaves to 3 to 4 inches long with pruning shears. Cut so the tops of the foliage slant down toward the ground on the right and left of the fan, so water sheds from the cuts when it rains.
Allow the cuts on the rhizomes to dry for several hours to prevent rot.
Plant the rhizome sections in the prepared garden area with the fan up and the rhizome piece horizontal and just barely below the soil surface any roots should be firmly buried. Sections should be planted 2 to 3 feet apart to avoid dividing again within the next three years, though you can plant them in triangular clumps with the fans pointing out to the points of the triangle, 8 inches apart, for a more natural effect, according to the American Iris Society's Region 14, which includes Northern California, Nevada and Hawaii.
Soak the ground with water immediately after planting. Allow the tops of the rhizomes to dry before watering again.
- Tulare County, in the San Joaquin Valley, is the home of the Porterville Iris Festival each April.
- Bloom time for bearded irises depends on location, but can begin as early as March and extend through April and May, according to University of California's Jepson Herbaria in Berkeley.
- Japanese and Siberian irises are usually only divided every 12 years. They divide in the same manner as bearded irises, though in the spring, instead of the fall.
- Dutch irises grow from bulbs rather than rhizomes and can be dug and separated every three to four years and replanted 4 inches deep and 6 inches apart.
- Yellow flag irises, which grow in moist soil along riverbanks and ponds, as well as in gardens, are considered an invasive species in most states, including California. Do not replant this species.
Patricia Hamilton Reed has written professionally since 1987. Reed was editor of the "Grand Ledge Independent" weekly newspaper and a Capitol Hill reporter for the national newsletter "Corporate & Foundation Grants Alert." She has a Bachelor of Arts in journalism from Michigan State University, is an avid gardener and volunteers at her local botanical garden.
Back Into the Ground
The once large clump of iris is now ready to go back into the ground as several smaller clumps. Leave at least 12 inches between the new iris plants. The planting depth is crucial to the health of the new iris plants. If you plant them too deeply, they won't flower.
The tops of the rhizomes should rest level with the soil line. Just barely cover the rhizomes with soil. A 1/2-inch layer of soil protects the rhizomes in an area with hot summers. Firm the soil around the transplants and give them a deep watering. Keep watering at the base of the plants only enough to moisten the soil.
The blooming of the bearded irises is something I eagerly await each spring. This year, I made a mental note that I should divide and replant the irises after flowering. That time is now! Here’s how to divide irises—with step-by-step pictures.
Even though my irises were planted years ago and are terribly overgrown, the blossoms were still gorgeous this spring. But dividing bearded irises every three to five years allows the clump to rejuvenate and bloom better (not to mention a way to multiply your irises to fill in gap). Also, it’s helpful to avoid the iris borer which is a very destructive pest typically attracted to older, over-crowded gardens.
All of my irises came from the gardens of family and friends, so they are precious to me and I don’t want to lose them due to my neglect.
When Should You Divide Irises
It’s important to divide and replant at the right time of year. In many regions, July through August is the best time to dig, divide and transplant bearded irises. You can probably get away with dividing through mid-September. Do NOT divide in the spring. You must do this job post flowering, during the summer.
This is hot, heavy work involving a lot of digging so I waited until the weather cooled down a tad before starting. My goal was to rework the iris beds, add some compost, get rid of the invading sedums and tree roots, and divide and replant the crowded rhizomes.
The irises are getting crowded and encroached upon by sedum. The bed they are in is narrow and next to large rocks leaving the irises nowhere to go.
Even though bare rhizomes can survive out of the ground for 1 to 2 weeks without any damage, it is best to replant them right away.
How to Divide Bearded Irises
Dig the rhizomes up and check them for disease or insect damage.
We found some borer damage and mushy rhizomes that we discarded.
Snap or cut off the old part of the rhizome since it will not flower again.
The roots are quite long and will help anchor the newly planted rhizome in place.
Amend the soil with compost and dig a shallow hole or trench. Make a mound of soil in the middle to place the rhizome on, spread the roots out over the mound and cover them with soil.
Leave the top of the rhizome exposed.
Next season’s plant emerges from the fan end of the rhizome so when replanting, face it in the direction you want plant growth to travel. Space the pieces 12 to 24 inches apart for tall types, closer for dwarf ones.
I planted mine closer, for a more immediate display, knowing that I will have to divide them again sooner.
It is easier to plant if you cut the tops back to about 6 inches tall.
Water well to settle the soil around the roots and continue to water deeply once a week until new growth appears. Once established, bearded irises are drought-tolerant and won’t need additional watering. Fertilize early in spring and again right after blossoming with compost or a low nitrogen fertilizer.
It was sweaty work, even on a cool day, but so rewarding to see it done. We had enough leftover rhizomes to plant another bed on the other side of the stone wall. Next spring we should have twice the blossoms!
Divide and conquer
To flower at their best, Bearded Iris need to be dug and divided every 2-5 years (depending on growing conditions and varieties). Now this might sound like it is a bit of work, but, it only takes a minute and then you can either increase your supply, or share them with family and friends.
Bearded Iris are ideally divided late summer to autumn, once they have finished their flowering. Moving them at other times is ok, but it will disrupt their flowering.
1. Simply dig under the clump with a fork or spade, ensuring you don’t run through the rhizomes as you do. Lift up the clump by the leaves and shake off any loose soil.
2. Once you have done this, simply separate your rhizomes by pulling them apart, they break as easily as Ginger.
3. You then trim the foliage to around 10cm. You trim the leaves to reduce the stress on the plant, leaving enough to allow photosynthesis, soon the plant will develop fresh leaves and the browned leaves can simply be pulled off.
4. It is important you replant your Bearded Iris within a couple of weeks after dividing, as they do not like to totally dry out – it leaves them susceptible to diseases and rot.
5. Prior to planting dig your soil to ensure good drainage. Bearded Iris need good drainage or they will rot. Dig your hole so the roots are beneath the soil, and the rhizome is sitting at the soil level, just exposed to the sun. In warmer climates, cover the rhizome with 1-3cm of soil to prevent scalding. Space your Bearded Iris 35-45cm apart.
6. Then you just need to water it in. Adding a seaweed tonic at this time will give your Bearded Iris a bit of extra get up and go.
And the job is done! It probably took you more time to read this than it will to actually do it!
Keeping your Bearded Iris happy is easy. You just need to give them a top dressing with a slow release fertiliser at the start of spring. Use one that isn’t too high in nitrogen as that will encourage leaf growth at the expense of flowers.
That is all you need to do have happy, thriving Bearded Iris.