Posted from 08/05/06:
It's summertime and the irises look dreadful. Is it okay to cut back the marred foliage now?
Yes! By removing any diseased foliage you will not only make your plants look better now but also reduce their exposure to future leaf spot infections.
Start by pulling off any withered leaves. Next, cut and remove any spotted or damaged leaves. Make slanting cuts a little lower than the lowest leaf spots. Dip scissor blades in a solution of 10 percent chlorine bleach between cuts.
Bearded irises are semi-dormant now but as soon as they reawaken, they'll sprout new leaves. Before you know it, your iris plants will look as fresh as they do in spring.
If you have different kinds of bearded irises, you may notice that the foliage of some varieties holds up better than others.
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By mid summer, the robust rebloomers tend to look better than the others. That's because the rebloomers, which bloom a second time in late summer or autumn, don't enter the same period of semi-dormancy in summer as other bearded irises. As long as they get adequate moisture and nutrients, they keep on producing new leaves.
If your bearded irises have grown too crowded to bloom well, now's the time to dig and divide the rhizomes. Plants with plenty of room bloom better and the better air circulation also helps them resist disease.
Most gardeners get best results by dividing iris plants every three to five years.
After you dig up your rhizomes, use a sharp knife to cut off sections. Each section should have its own fan of leaves.
Discard the old centers as well as any soft or rotted spots. Trim the leaf fans back to about six inches.
Choose a sunny spot with well-drained soil. After adding compost and a slow-release fertilizer, plant the rhizomes 12 to 15 inches apart. Spread the roots over a mound of soil, with the top of each rhizome barely covered by soil.
Rebloomers often require division even more often than other bearded irises, but there's a catch. Disturbing the plants now means you'll sacrifice the late-season blooms. The Reblooming Iris Society recommends dividing only half your plants at a time and leaving the rest to keep on blooming.
If coddling irises sounds like too much hassle, try Siberian irises instead. Their flowers aren't as large and the choice of colors not as extensive, but Siberians offer resistance to both foliage disease and iris borers.
Division is seldom, if ever, necessary. The plants are also more tolerant of shade than bearded irises.
You don't even have to remove the old flower stalks. Allowed to remain, they develop attractive seed pods that persist through winter.
