When iris begin to form a solid mat, it is time to begin thinking about dividing. Some people wait until flowering starts to taper off, but by then the simple chore has become challenging (I speak from experience).
Weeds love to lodge themselves where it is almost impossible to remove them without damaging the meaty rhizomes of the iris. Dividing provides an opportunity to clear out the weeds in the process and start anew with a clean bed.
Using a fork or shovel, lift the whole mass of tangled rhizomes and tease them apart.
Some of them will be spent and shriveled. Close examination will reveal holes where borers have penetrated some of the healthier looking parts. All of these should be broken off and discarded.
Once the healthy sections with vigorous leaf growth have been separated and brushed free of dirt, the leaves should be trimmed to about 6″.
Make a hole about 3″ deep and wide enough to spread the roots. Make a mound in the center of the hole upon which to place the rhizome.
Fill in, covering all of the roots, but leaving the top of the rhizome showing. Water in well, and that’s it. The new transplants may skip a year of blooming, which is why I like to stagger my transplanting. I plan to keep closer tabs on their progress and label the various colors so that I can plan placement better. The fans of lance-shaped leaves make a dramatic contrast to other leaf shapes when used strategically, so I spread some of these around where I think they will make an impact, and still had plenty to share with neighbors. Come spring, I hope to get some shots to show you the fruits of my labor. Oh, and mid-August through September is the best time to tackle this job.