Well here's what I recommend. In the fall, right after frost lightly blackens their foliage, dig the clumps, hose them down to wash away the soil and after they dry, put them in a loose mix of sawdust, perlite or some other dry storage material. Then, put them in a cool, dry, dark place for the winter. If you live in a frost-free location, you don't have to do this. Then, if the spring, after frost danger has passed, take a sharp knife and simply cut the root mass into pieces, making sure each piece has at least one or two ""eyes"" or growth spots. It's very easy and you can't really hurt the plant. If you want to divide a plant that's already growing, dig it, and cut it the same way, but I recommend doing this at the beginning of the season and not disturbing the plant when it's growing.