Make sure your plants are well watered a day or two before you plan to split them.
Before you put a shovel in the ground, have a game plan in place for where the new divisions will go—you don’t want them to dry out while you look around for their new home.
To reduce moisture loss and help your plant recover faster, trim back the foliage by at least half. I sometimes only leave about 6 inches of growth above ground—don’t worry about this drastic haircut, your plants will grow it all back!
Prepare the planting space (amending the soil as needed) and, if you have lots of perennials to split, keep a bucket of water nearby to keep the roots moist while you work.
If you can’t replant the divisions in the ground right away, put them in containers until you have a permanent place in the garden for them.