Irises bloom on long, slender stems above a fan of rich green foliage. These hardy perennials return each year, increasing in size and abundance in blooms. Decreased blooms or overcrowded rhizomes -- a swollen root similar to tubers or bulbs that store food for next year's blooms -- indicate that it's time to divide the plants. Irises require minimal care other than occasional pruning and light mulch for winter.
Remove flowers when the colour fades or petals drop. Cut the stem to the base of the plant with a pair of garden clippers or a sharp knife.
Divide overcrowded irises after they bloom in the late summer or early autumn. Cut foliage back to 15 cm (6 inches). Dig under the entire clump with a spade or garden fork and lift the plant free from the soil. Shake excess soil from the rhizomes and roots. Place irises in a shaded, dry area for 24 hours to dry. Brush off dried soil.
Separate rhizomes so that each section has at least one eye -- a small indentation where a bud forms. Generally, a shoot of foliage will be present at the eye. You can pull some rhizomes apart by hand, but you will have to cut others with a sharp knife.
Plant rhizomes in a prepared bed with similar soil and lighting as the original growing location. Place in loose soil so the top of the rhizome is 1.25 cm (1/2 inch) above the soil level. Spread out the roots at the bottom of the rhizome on to the soil. Cover all roots. Water thoroughly.
Prune mature irises that have not recently been transplanted back to 15 cm (6 inches) from the ground in the autumn.
Mulch irises with 7.5 to 10 cm (3 to 4 inches) of hay or straw to prevent damage from freezing and thawing during winter months.
Irises transplanted in late summer or early autumn bloom the following spring or summer.
Water irises during periods of drought.
Apply balanced fertiliser after irises bloom if foliage lacks rich green colour.