When to Cut Back Iris Stalks

Types

• While many species of iris are available to home gardeners, bearded iris, Siberian iris and Japanese iris are the most common. Bearded iris is available in nearly every color and in sizes ranging from dwarf to plants measuring 4 feet tall. Bearded iris prefers full sunlight and well-drained soil. Siberian iris is a slightly sturdier plant because it grows from roots instead of rhizomes. Siberian iris, which displays colorful, beardless blooms, grows in either partial shade or full sunlight and a variety of soil conditions, including wet, boggy areas. Like Siberian iris, Japanese iris thrives in moist soil. Its big, ruffled blooms are shaped differently from bearded and Siberian iris.

Cutting Back Procedure

• Iris foliage is cut to within 2 to 3 inches of the ground when the foliage turns brown in autumn. Depending on the climate, the foliage often doesn't turn brown until the first hard frost of autumn. Never cut the foliage while it's still green because it stores energy that feeds the plant for the coming growing season.

Disposal

• Iris foliage often carries spores of fungal disease that can be transmitted to other plants. To prevent spread of disease, burn the cut foliage or place it in a sealed bag and dispose of it in your trash. The foliage should not be put on a compost pile.

Care Afterward

• A thick layer of mulch is important in climates with cold winters because mulch protects the iris rhizomes from heaving of the soil caused by repeated thaws and freezes. Apply about 6 inches of compost or loose mulch, such as straw, after the ground freezes in autumn. Removing most of the mulch when the ground thaws in spring allows sunlight and air to dry the surface of the soil. Wait about one week, and then remove the remainder of the mulch.

Division

• Late summer, about one to two months after the iris ceases to bloom, is the time to divide the plant. Iris doesn't require division every year, but dividing the plant every three to five years keeps the clump healthy and prevents it from becoming too crowded. To divide iris, dig the clump with a spade or garden fork, and then separate the rhizome sections with a sharp knife. Plant the rhizomes immediately, or store them in a cool, well-ventilated spot until spring.