The summer of 2011 has been a very hard year for drought here in the midwest and the lower middle states. Texas and Oklahoma have set records for highest temps and longest running days over 100 degrees. We have been getting calls almost every day from our customers asking us if they should be watering their irises.
Here's my answer to that question and I hope it helps you a little. It is natural for most irises to go dormant in hot, dry weather conditions. We don't water our iris in the fields in any way during the summer months. We went for over 2 weeks here with daytime temps over 100 degrees and the irises are fine. If you were watering some as the drought progressed, it is probably ok to continue right on through the summer. I would have watered sparingly. Too much water in hot temps can and will sometimes rot the rhizomes. If you did not start out in early summer watering, I would not do so, until the temps begins to break. My thought is if you start watering too early in the hot temps, and the plants break dormancy too soon, you may burn the new growth up. The plants that have not been watered through this period will often look discolored and they will not have full fans. This is normal. The rhizomes have stopped growth and pulled the nurtients back to conserve energy.
We also get the question, "Will they die from this drought?" I doubt that there will be many losses, but it is possible that some varieties just won't take the weather and die. I am almost certain, that the losses will be minimal if the water issue is kept in check.
The water grown irises are the exception to these ideas. Water irises should not be allowed to dry out in any circumstances in droughts. Hard baked ground is a recipe for losses in these irises. I am guilty of letting them get pretty dry, but I always come through with a good watering before they it hurts them.
The photo I have posted is typical tall bearded clump that has been through the drought with no water except one 1/2 inch rain two weeks ago. The next day after the rain, the temps went to 104 degrees.
I hope this post makes a few of you sleep a little better helps you if you have not been watering and you need to know when to start again. God Bless you and your gardens. Please remember our troops and our befuddled government.