Tips on Iris Bulbs

Most irises begin to bloom in the spring. image by Rob Tello/


Irises are attractive plants that grow tall with vibrant blooms. They are available in many different colors and varieties. While iris root balls look like bulbs, they are actually called rhizomes. Below the rhizomes, thin stringy roots fan out. With the proper care, irises will adorn your garden with blooms during the spring and summer months.

Step 1

Plant new iris rhizomes in early fall, usually in September, in an area that receives full sunlight. The sooner your get them in the ground in the fall, the more likely they will bloom the next year, especially in colder climates. If they do not bloom the first year, they should bloom the second year. At a minimum, rhizomes should be in the ground before the first freeze. You can also plant irises in the spring, but they will not bloom the first year.

Step 2

Plant iris rhizomes just below the soil's surface in well-draining soil. Dig a hole two to three times the width of the rhizome, and spread the roots out along the bottom of the hole. Be sure to tamp down the soil so there are no air pockets, which can later cause root rot. Water and tamp down a second time to remove any additional air pockets. Space irises about one to two feet apart. The closer together you plant them, the more thinning out will be necessary in subsequent years.

Step 3

Thin out iris rhizomes every few years. As the rhizomes multiply and grow close together, they stop blooming. They will continue to grow but will not bloom. To do this, after the irises bloom and go into a dormant stage, use a shovel to dig up the entire plant, including the rhizome and roots. Cut off the stalk and leaves a couple inches above the rhizome, and cut the roots three to four inches below the rhizomes. Plant in a new location.

Step 4

Store iris rhizomes indoors during the winter in climates that are extremely cold. Dig up the rhizomes, and cut off the stalks. Cut off the roots, so they are three to four inches long. Sprinkle some sulfur on the roots, and store them in an open container with moistened peat moss. Store in a dark and cool location, such as a garage, crawl space or attic. Check on the rhizomes periodically during the winter to be sure they are not shriveling up or rotting. If they are, add a bit of water to the peat moss. Plant the rhizomes back in the garden as soon as you can dig into your ground.

Things You'll Need

  • Trowel
  • Shovel
  • Water


  • North Dakota University Extension Service
Keywords: iris rhizomes, plant iris, thin iris

About this Author

Melissa Lewis is a former elementary classroom teacher and media specialist. She has also written for various online publications. Lewis holds a Bachelor of Arts in psychology from the University of Maryland Baltimore County.

Photo by: Rob Tello/