July 29th, 2003
Iris Rot in Bearded Iris
Overcrowded and smothered by dead leaves, these bearded iris rhizomes are in danger of developing iris rot during the hot, humid summers in Central Texas.
Reader Janette Boley asks for help combatting iris rot.
When the weather’s hot and humid, bearded iris rhizomes have a tendency to turn to mush. When the temperatures hit the 90s, you should not feed your irises. If you water at all, you should water carefully–deeply, but infrequently. Never allow water to stand on iris rhizomes. Water in the morning so that the rhizomes can dry out in the sun. And do not bury the rhizomes under the dirt or mulch them. Irises can survive the summer with very little water, although their will yellow and turn brown. They’ll come back again in the fall.
Irises need a lot of air circulation. Iris leaves open out in a fan. The outer leaves are the oldest ones and when they turn brown they should be stripped off.
There is no getting around the fact that irises have to be dug up every few years to do well. When the rhizomes start growing into each other or on top of each other, dig them up. Crowded rhizomes are subject to rot. When they are crowded, there is no room to grow, store up strength for next year’s flowers.
If you’re careful, you can dig out the old rhizomes (the ones that already bloomed and don’t have fans) without digging up the whole bed.
If, despite all precautions, you get rot, dig out the affected rhizomes immediately. Don’t let it spread. If they are not too far gone, you can save them by soaking them in a 10% bleach solution and scraping all the rot off. Then let them dry until the rotted part scabs over. Replant them far away from other irises.
by M Sinclair Stevens