|How do I transplant iris and when? How deep to plant, etc.
|It is a good idea to dig up rhizomatous irises every 4-5 years so you can separate the weak and diseased ones. Then at the same time to can amend the soil a bit. They'll love you for it!
After blooming lift the entire clump with a spade and separate it into small clusters of rhizomes (this is what the roots are called). Choose only the largest and healthiest-looking ones for transplanting. Put them in a bucket while you work the soil for the new planting. You might also add some compost or rotted manure as they enjoy rich soil. Good drainage will help you avoid borers.
Place one or several of the divisions into the prepared soil. If you plant them in a circle be sure to have the leaves facing outward. If you don't do that, they will soon be crowded again. Make the holes deep and wide enough to take the roots without crowding. Have the rhizomes set so they are just below the surface of the soil.