I don't cut roots even when they are completely shriveled and deader than dead because they can still help anchor the plant in place until the new roots grow out. With all the animal traffic through my beds, the new transplants need as much help as they can get to not be uprooted during those first couple of months.

I also can't see any reason to cut off viable roots that can immediately start absorbing water and feeding the plant. Many roots on rhizomes that have only been out of the ground for a couple of weeks are still fully viable.

Laurie

I cut off most of the roots if I pot or if the plants are going to be out of the ground for a long time.

I think cutting off the roots encourages those little yellow root nubs to form. When finally placed in the ground, they send out roots very quickly and anchor the plant.

I don't think those deader than dead roots will send out any new roots, particularly if they are the 'mart' irises in bags of peat moss.

Another reason I've heard for trimming roots was to prevent importation of nematodes. If the roots have nodules or are forked, supposedly those are signs of nematode damage. I cannot verify that because I cannot see microscopic critters with the naked eye.

Walter Moores

Deader than dead roots don't send out new roots, but the rhizomes they're attached to sure do. And those dead roots will still help anchor the rhizome until the new roots grow out.

I haven't noticed nodules on any of my iris roots, but I can instantly tell which bed I dug a rz out of because the rzs dug from heavy, clayey beds have thin, short roots with many forks and shallow feeder roots. Rzs grown in beds with improved soil have thick, long, fleshy roots with few forks and and none of those tiny feeder roots.

Laurie