How to Trim Iris Rhizomes

Dividing helps encourage more iris blooms the following year.

Irises bloom in early summer, growing tall stalks topped with colorful, drooping blooms. The green, strap-like leaves provide background color to the flower bed for the rest of the season. The plants grow from an underground tuberous root called a rhizome. The rhizome collects and stores nutrients throughout the summer months, spreading and becoming larger each year. After two or three years, the rhizomes become overcrowded. Trimming the rhizomes improves the amount of iris blooms while also giving you new root sections if you wish to expand the iris bed.

Things You'll Need

• Spading fork
• Knife
• Shears

Instructions

1. Brush the soil away from crown of the iris plant to reveal the rhizomes. These sit right at or slightly beneath the soil surface.

2. Loosen the soil around the rhizomes with a hand-held spading fork, taking care not to cut or pierce the roots. Slide the fork under the rhizomes and lift them from the ground.

3. Brush as much soil from the rhizomes as possible, so they are easier to inspect. Cut the foliage back to one-third its height, using a pair of sharp shears.

4. Cut apart the rhizomes with a sharp, clean knife. Remove the sections on the outside of the clump, cutting the sections so each has two to three leaves or leaf buds on it.

5. Discard the rhizome parts from the center of the clump, as these are older and likely beginning to decline in vigor. Also dispose of any root sections that are soft, mushy or show signs of disease. Save only the younger sections that are firm and have a texture similar to that of a potato.

6. Replant the trimmed rhizomes in the bed immediately, spacing them 12 to 24 inches apart. Plant the extra sections in a new bed.

Tips & Warnings

• Trim and divide iris rhizomes in midsummer when they have finished blooming for the year.

References

• Purdue Cooperative Extension: Dividing Iris
• Colorado State University Extension: Iris, Iris Everywhere