Soft rot attacks during wet seasons in poorly drained soil, entering though wounds in the rhizome made from premature leaf removal or too-close cultivation; it can also be carried on the body of the iris borer. The eggs of this pest
hatch in spring, producing 1- to 1½-inch-long, fat, pinkish larvae. The larvae enter a fan at the top and tunnel down toward the rhizome, where they may eventually eat the whole interior without being noticed.
In fall, remove dead, dry leaves, which often carry borer eggs, and destroy badly infested fans in spring. You can also crush borers in the leaves by pinching toward the base of the telltale ragged-edged leaves or by running your thumb between the leaves and squashing any borers you find. They are also vulnerable when you divide the clumps; check every rhizome for this pest. If you find a few borers, try cutting them out, but destroy badly infested rhizomes.
Siberian irises enjoy similar conditions to bearded irises, tolerating wetter soil and requiring less frequent division in spring or fall. Be certain to replant as soon as possible after dividing them. Rot and borers seldom plague them.
Grow Japanese irises in much the same way, providing shade from the hottest sun. Water well before and during bloom. They need acid soil and benefit from a few inches of mulch in summer.
Plant reticulated irises in fall about 3 inches deep and a few inches apart in average to more fertile, very well-drained soil
. Grow with annuals and perennials to fill the gaps left by their leaves, which wither by summer.
Landscape uses: Smaller bearded irises are perfect in rock gardens and along paths and beds. For mid- to late-spring bloom, plant taller ones in a perennial border, or in a separate bed to provide optimum conditions. They also look splendid among garden ornaments and along patios. Siberian and Japanese irises are good choices for borders and wet sites, such as along a stream or the edge of a pond, although they prefer slightly drier conditions in winter. Reticulated irises look at home among rocks, naturalized in thin grass, or at the front of borders.