Varies by type. Beware of planting rhizomes too deeply or covered with too much mulch, as they may rot. Plant bearded irises from mid-summer to early fall.

A vast genus or both perennials and bulbs, 300 species and thousands of cultivars. Foliage is sword shaped, strap shaped, or grassy. Some rhizomatous species spread widely, other form clumps.

All bear flowers with 6 petals. Three, called standards, point up or out. And three, called falls, point out or down. Generally flowers are borne in small clusters and buds open in succession along the stalk.

Bearded irises prefer average to rich, well-drained soil. Whereas bog irises need permanently damp soil or even to be placed at a pond margin.

If you fertilize, which may not be needed if your irises have good green foliage, use half a cup of 5-10-10 fertilizer per clump after flowering. Do not apply directly to the rhizomes, as it could burn them.

To prevent seeding, cut back the stalks to 1-2" above the rhizomes, after the flowers have faded.

The most serious problem is bacterial soft rot, which you will recognize from mushy, foul-smelling rhizomes. To prevent, do not use manure or excess nitrogen, especially with poor drainage. If soft rot occurs, dig up and destroy the effected portions of rhizome