How to Divide Irises for an Everlasting Supply of Blooms

Irises are a beautiful addition to the garden, yielding tall statement flowers that add height and color to any landscape. Not only are irises eye-catching to look at, but they're also one of the easiest plants to propagate through division. To help you through this process, we consulted a master gardener and landscaper, who shared tips for dividing irises, including how and when to do it.

Importance of Dividing Irises 

Gardeners usually divide irises for two reasons. “First is to multiply the number of available irises to spread and fill up a space,” says Eric Preston Stout, a master gardener and landscaper. The second reason is that the plant needs room to grow, or it will have to compete for nutrients with other plants. “Dividing any herbaceous perennial—like the iris—will prolong the plant’s life and provide the necessary nutrients and resources to produce bigger flowers," says Preston. What's more, these plants are beautiful gifts to divide and give to fellow gardeners. 

Signs It’s Time to Divide Irises

There are a few signs it’s time to divide irises. “If the plant looks messy, crowded, or simply ugly, it’s time to divide,” says Stout. When an iris has gotten too big and is crowded by other plants, it will compete for nutrients, causing the blooms to lose their vibrancy and color. Stout says he usually divides irises when the plant has grown two times or three times bigger from the first year’s blooms. 

Best Time to Divide Irises

Depending on how fast your iris grows, aim to divide it every two to four years. When you decide to divide your iris, the best time of the year to do so is about four to six weeks after its last bloom cycle during your region’s drier season, says Stout. “Never divide on a rainy day, as the abundance of moisture can lead to disease and or fungus,” he says. 

How to Divide Irises

Follow these steps when dividing irises.

1. Remove the Iris

Using a shovel or spade, carefully remove the iris from the ground. Try to lift the entire clump of rhizomes or bulbs (depending on the variety) from the ground at once. Shake or rinse off excess soil from the clump. 

2. Trim the Vegetation

Trim all the vegetation above your rhizomes or bulbs until it is about one-third of its original size. That way, the plant can re-establish its roots without directing its energy to supporting a large amount of foliage.

3. Separate Your Irises

Some rhizomes or bulbs can be separated by hand, but others (especially the rhizomes of large irises) will need the help of clean garden pruners to cut them apart. Using pruners, divide the rhizomes into pieces that are about 3 to 4 inches long. Make the cuts where the rhizomes have started to fork. Each piece must have at least two blades of healthy foliage and a root ball for the iris to regrow.

4. Remove Unhealthy Rhizomes

Remove unhealthy, soft, or diseased rhizomes to keep your irises thriving. Healthy rhizomes lack noticeable cuts and discolored spots and feel firm. Meanwhile, unhealthy rhizomes have areas that may appear rotted or damaged by insects.

How to Replant Divided Irises 

After dividing your irises, replant them following these steps.

1. Choose a Location for Planting

Pick a spot to plant the bulbs or rhizomes. Most irises prefer full sun and about six hours of sunlight throughout the day, but check the preferences of your specific variety before choosing a location. 

2. Prepare the Soil

Add compost to your soil to ensure it has enough nutrients. Also, consider your soil’s water drainage, as irises cannot handle soil that isn't well-draining. If in doubt, an iris can easily thrive in a raised flower bed or flowerpot.

3. Replant the Iris

Dig a shallow hole and replant the iris so that the top of each rhizome or bulb sits at the soil level or just below it. Don’t place the iris too deep in the ground since rhizomes planted too deep can struggle to establish roots and are susceptible to root rot. Plant your iris no closer than 18 inches away from another iris or you will need to divide and separate your irises again soon.