The care information provided in this section represents the kind of practical advice is available for all the plants in this web site if you subscribe to the monthly customized newsletter Yardener’s Advisor.
At planting time or every spring sprinkle a general purpose low-nitrogen granular fertilizer on the soil near the irises. Do not allow it to fall on the exposed parts of the rhizomes. As with other bulb plants, do not use manure.
Mulching and Weed Control
Mulching is recommended for rhizomatous irises only in the winter. Cover iris beds with mulch before the first hard frost. This will insulate the soil somewhat against the typical alternate freezing and thawing of winter. This will minimize soil heaving and disturbance of the shallowly planted rhizomes. Rake away the mulch in the spring to allow sunlight to reach the rhizomes. For more information see the file on Using Mulch
Although irises are generally drought resistent, newly planted irises should get 1 inch of water a week from rain or from a watering system, to help them become established. Afterward, water them only during spells of hot, dry weather. For information on products see the file on Choosing Watering Equipment
Pruning or Grooming Iris
Iris leaves often brown at the tips in the summer. If this is obvious, cut off the browned tips. Cut back iris flower stems after the flowers have faded. Do not, however, cut the leaves back severely after flowering. The plants need their leaves to store up energy for next year.
Iris Division and Propagation
To acquire more iris plants and to keep them blooming at their best, divide them every 3 to 5 years. Do this either in the spring or early fall. Carefully dig up the knarled clumps of rhizomes and wash them off with the hose. Slice these clumps into sections that include some roots and a fan of foliage with a clean, sharp knife. Either let these rhizomes dry off in the sun for a few hours, or dust them with sulfur or captan to ward off disease. Then replant the most vigorous ones. Discard any that are soft, or show signs of borers [see below]. When dividing in the fall, trim back iris foliage for easier handling. Newly divided clumps of iris may not bloom the following season. With good soil conditions and an annual application of fertilizer, most clumps will bloom within a year or two.