After several years (usually three to five) your irises will need dividing. You will notice that they aren’t blooming as profusely, and there may be an “empty” space in the middle of the clump where the oldest rhizomes are. This is how you’ll know it’s time to divide your irises. The best part is, not only are they easy to divide, but you’ll have extras to grow or share!
When to Divide: Irises are ready to divide four to six weeks after they finish blooming. The flowers will have dried up and the tips of the leaves may be starting to turn brown and die back. This is normal. You’ll need a spading fork (preferred) or a shovel, a pair of scissors, a Sharpie marker, and access to a hose.
Lifting a Clump: The best way to lift a clump of irises is with a spading fork. You can use a shovel, but a fork will leave more of the roots intact. Shove the fork into the ground about six inches past the outer edge of the clump and pry up a bit. Do this all the way around the clump until it is loose and you can lift the whole clump out of the ground. Shake the dirt off the roots as best you can. If the dirt is sticking in clumps, you can hose the dirt off.
Labeling your Irises: Labeling is critical! Once your irises are dug, they all look alike. Label the fans of each clump with your Sharpie to prevent accidental mix-ups. If you plant to lift and divide more than one clump, we suggest doing it one clump at a time so you can label them as you go. If you need to dig several clumps at once, be sure to label them as soon as you dig them up, including any loose fans whose rhizome looks like it might fall off.
Dividing the Clump: This is what a clump of irises looks like. The center rhizome is the “mother” and it is spent. Time to get rid of it. Also, the round stalks where the blooms were also will not bloom again. The red lines on the photo show one way you could divide this iris. See the “pup” on one side of the left rhizome? That will be a new iris fan next year. Watch for pups! They are worth keeping. You can cut the rhizomes apart with a knife or just break them off. Let the cut/broken end dry a bit before replanting them, and be sure to discard any rhizomes that are mushy or have a foul smell.
Trimming: Trim the fans back to about six inches long, using a scissors. This will encourage good root growth when you plant them. You won’t hurt the iris – those fans will die back in the fall anyway. You may also trim the roots to about six inches long to make the rhizomes easier to plant. BE SURE EVERY FAN IS LABELED! We can’t stress this enough.
Here’s an excellent video on dividing irises from the Presby Memorial Iris Gardens in New Jersey.
Sharing Your Irises: If you have more irises than you want to replant, (a common problem) there are several fun things you can do with them. First, consider donating rhizomes to the annual HIPS Rhizome Sale. This is our major fundraiser, and we rely on donated rhizomes to make the sale a success. Watch for information on the Rhizome Sale in the Spring issue of ROOTS.
Other ways you can share irises are to give them to friends and family, youth groups at church, scouting groups, or nonprofit organizations who may wish to sell them as a fundraiser. There might be a beautification project in your area that would welcome them. Be creative! And if you have a good idea for sharing, please let us know. Contact us at [email protected].