Arilbreds tend to drop their roots during summer dormancy, but some of the
quarterbreds I dug this weekend had held on to enough to measure. El Gigante
had the longest, with some exceeding 18".
I should add that it's not at all unusual to find iris roots over a foot deep
when renovating beds. My own practice is to remove the old roots before
planting. Some years ago, I experimented with leaving 4 to 6" of roots on
1/4-breds & TBs, but when I dug them the following year those plants seemed to
have put out fine feeder roots on the old stubs rather than devoting energy to
growing long, new roots. Here, a deep root system is essential to survival.
Sharon McAllister (email@example.com)