Gardeners growing irises must divide and move them every three to five years for optimal blooming. If you allow irises to become crowded in a growing area, blooms will decrease and deteriorate. Move iris plants in midsummer to allow them ample time to acclimate to their new homes before winter temperatures set in. The following spring you will see an abundance of iris blooms to reward your hard work.
Water the area where the irises are growing two days prior to digging them up. This will ensure that the soil is moist enough to work in.
Dig up the entire iris clump. Iris rhizomes and roots grow shallowly, so it will not be necessary to dig far into the soil to remove these completely.
Cut back the iris stems growing from the rhizomes by approximately one-half to make handling the rhizomes easier.
Break off any small portions of the iris rhizomes that appear inferior or damaged. Discard these pieces. Break off the oldest portion of the rhizome also (the part farthest away from the part of the rhizome that is growing foliage). Discard the oldest rhizome portions.
Break up the larger rhizomes that remain so that each separate part of the rhizome has a viable stem growing from it. These separated rhizomes will be suitable for planting.
Discard all of the foliage, stems and rhizomes in the trash or in a compost bin. Do not leave any iris plant debris on the ground near the growing area because this could lead to an iris borer infestation.
Prepare a new growing area by working the soil with the garden spade down to a depth of 3 to 4 inches. Add 1 to 2 inches of compost to the top of the soil and work this in well with the garden spade.
Dig new holes for the separated iris plants. Make them just deep enough to accommodate the root systems. Plant three to five iris rhizomes together in a circle, making sure that the portions of the rhizomes where the stems are growing from is facing outward so the irises will grow away from each other.
Make a small mound in the center of each hole and place each rhizome onto a mound, arranging the roots around the edge of the mound. Fill the hole with soil, making sure the rhizome is just barely under the soil surface. Water the newly planted iris rhizomes generously.