Dividing & Transplanting Irises: A Step-By-Step Guide

When well cared for, iris plants will need divided on a regular basis. Learn how to do it right here.

blue iris flower
(Image credit: GrahamM Creative / 500px / Getty Images)

With over 100 varieties of irises, there are many colors, petal shapes, and levels of showiness you can choose from. After finally deciding and planting your iris, you may find that you put your plant in the wrong spot. Or, you may need to divide your iris and transplant the babies elsewhere. Transplanting an iris is a routine part of its care, but many gardeners don't know when or how to move it to a different space. Keep reading to learn the answers to these questions and more!

Bearded vs. Siberian

First, you should determine whether you have a bearded or a Siberian iris. Both bearded and Siberian irises are excellent additions to the home landscape, but each have different needs. While bearded irises are best known for their large, colorful blooms, Siberian iris types have long been praised for their ease of growth and ability to multiply quickly. Large beds of these species will continue to bloom, even after becoming crowded. Bearded iris will generally require division on a much more frequent basis to keep the plants looking their best.

Signs You Need to Divide an Iris

Learning when to transplant irises will vary depending on the type, but most will show many of the same signs when it is time for division. Large groups of plants will produce impressive mounds of foliage. Though these leaves can be quite beautiful, beds that have become too crowded may see a decline in overall health. For example, the rhizomes may start heaving out of the ground. Overcrowded iris rhizomes will push on each other, which results in the entire root system literally pushing themselves out of the ground.

Decreased flowering will also be a key signal that plants may need to be lifted from beds. If you check the roots, they may look like a mass of snakes or a pile of spaghetti, which is a sign that they must be divided.

When to Divide & Transplant Irises

Determining when to divide irises can be difficult for beginner growers. Digging out the plants in spring or fall may be tempting, but doing so may interrupt their natural growth cycle. It's best to wait until the flowers have finished blooming, which makes mid-late summer the ideal time to divide clumps. Learning more about this process and about transplanting irises back into the garden will be essential in helping perennial beds to thrive season after season.

How to Divide Irises

  1. Dig - Irises multiply through the production of underground rhizomes. Each of these structures must be removed from the ground and separated to divide the plants. This can be done with the use of a garden spade or fork. Working in a circular motion around the perimeter of each plant, start by lifting the clump of iris plants out of the ground. If possible, lift the whole mass out whole, but if you can't do this, carefully break the clump into smaller parts and lift these out. Excess dirt should then be knocked free or rinsed from the plant, giving a clear view of the root mass.
  2. Divide - Dividing irises begins next. While some rhizomes can be easily separated by hand, others may require a clean, sharp garden blade or bypass pruners to cut each apart carefully. Each iris rhizome should be divided into pieces that are 3 to 4 inches (8 to 10 cm) long and consist of a few essential parts: at least two blades of healthy foliage and a small segment of root ball.
  3. Discard Unhealthy Rhizomes - Though uncommon, you may encounter rhizomes that look weak or show noticeable signs of disease. Healthy rhizomes should be firm, not soft, and lacking noticeable cuts, spots, etc. Unhealthy rhizomes include those that have rotted, decayed, or been damaged by insects. These rhizomes should be removed from the garden and disposed of immediately. Diseased rhizomes should never be added to the compost pile. This will help to prevent the recurrence and spread of disease within iris beds. If you have any sections of rhizome that have no leaf fans. These can be discarded as well.
  4. Trim Foliage - You should trim back plant foliage before or after division. This can be done by clipping each leaf back to approximately one-third of its height. Trimming back leaves at this time will help keep new plants healthy and aid in their preparation for the winter season.

How to Transplant an Iris

  1. Choose a Location - Iris transplants will grow best in full-sun flower beds, receiving at least 6 to 8 hours of light daily. Adequate sunlight will be vital to the production of flower buds. While irises grown in exceptionally warm climates will benefit from afternoon shade, too much shade may negatively impact their growth, resulting in decreased or complete loss of flowers.
  2. Prepare the Rhizomes and Soil - Once the iris rhizomes have been divided, you can replant them. First, trim the leaf fans back to about 6 to 9 inches tall (15 to 23 cm). This will allow the plant to re-establish its roots without having to support a large amount of foliage. Irises require well-amended growing beds with high soil fertility. The addition of compost and other organic matter is common. Particular emphasis should also be placed on drainage, as irises cannot tolerate waterlogged soils or drain poorly. These plants are quite adaptable to growing in raised beds, containers, and pots.
  3. Don't Plant Too Deep - At planting, special attention should be given to depth. Rhizomes planted too deeply may struggle to establish themselves within new beds, resulting in decreased production of flowers. Make sure to position your plants so that the top of each rhizome sits just below or at the soil level. If planting several irises near each other, point the rhizomes away from each other and space them 18 inches (46 cm) apart. Spread the roots out around the rhizome and then cover the roots and the rhizome with dirt.

Post-Transplant Iris Care

Once situated in the garden, new iris plants require little care. Watering beds deeply after planting promotes growth and the production of new roots. Establishing a robust, healthy root system will be essential for each plant’s winter preparation. Though your irises may start making new leaves after being transplanted, they should still be trimmed back in autumn.

Heather Rhoades
Founder of Gardening Know How

Heather Rhoades founded Gardening Know How in 2007. She holds degrees from Cleveland State University and Northern Kentucky University. She is an avid gardener with a passion for community, and is a recipient of the Master Gardeners of Ohio Lifetime Achievement Award.