Caring for Iris

Early Spring

Remove mulch. Soon after the snow melts in spring, remove the top layer of any protective winter mulch to allow air and sunlight to dry the surface. Wait a few days before removing the rest of the mulch, taking care not to break the center sections of fans where flower buds are developing.

Late Spring and Summer

Fertilize. As growth begins in spring, apply low-nitrogen fertilizer around established plants. Compost or a low-nitrogen controlled-release fertilizer is ideal in spring, paired with a high-phosphorus fertilizer in fall. In the coldest climates (zones 3 through 5), don't fertilize after mid-July to give plants time to harden off before winter.

Mulch. Lightly mulching new plantings is important. It prevents sunburn in the hottest regions. In the coldest regions, it prevents freezing and thawing of soil, which can kill the shallow-rooted plants.

Water. Irises need regular water throughout the growing season, but especially until six weeks after flowers fade. It's during this period that the next season's growth is initiated. Established clumps are drought tolerant and don't need water except in areas where there's little rainfall.

Deadhead. After blooms fade, cut flower stalks close to the ground, leaving healthy green leaves in place to nourish next year's growth.

Fall

Remove dead leaves and debris in late autumn, then trim the foliage back by two-thirds after the leaves have died back. In cold-winter regions, cut back the tops to about 6 inches after the first hard frost, and rake up any debris. After the soil freezes, mulch with 4 to 6 inches of loose compost or weed-free straw.

Dividing Iris

Lift and divide the rhizomes every three to four years. Without division, both the quantity and quality of blooms will diminish. Do it after flowering in the optimum planting time for your area.

Rhizomes are easy to pry up with a garden fork or shovel. Pull clumps apart, replanting the thickest, firmest rhizomes; these are usually the ones that have grown during the current season. Throw away the oldest, leafless rhizomes, usually at the clump's center. Trim leaves to about 6 inches long, then let all the cleaned and groomed rhizomes air-dry overnight. Before replanting, amend soil with lots of fresh compost or organic matter.

Content provided by the National Gardening Association.