All of your favorite spring-blooming perennials can be dug and divided now, giving them plenty of time to settle their roots over the winter to bloom next year.
The list of plants to divide now includes: daylilies, iris, sweet violets, oxalis, thrift, candytuft, Shasta daisies, coneflowers and St. Joseph’s lilies (hardy amaryllis), among others.
In March when the soil warms perennials will be peeking out of the soil, putting out new growth buds and showing signs of life. By then, their roots will have become established in cool, wet weather and be ready to spring forth.
You can use a spading fork or shovel to dig up the existing clump, just be sure to start digging far enough out from the central crown to get as much root as possible and to avoid damaging the crown.
Separate the clump of the original plant into sections with roots and cover them or put them in the shade while you prepare the soil they came out of. Dig organic amendments into the soil. This could include compost, peat moss, ground pine bark, etc.
When you have enough prepared planting holes for the divisions, put the healthiest cuttings in and surround the roots. Water the plant in and re-level it so the crown is right at soil level. Continue to back fill the hole and water the soil down.
Mulch the new plantings, keeping the mulch well away from the plant's crown. Don't fertilize in the fall or winter; wait until Feb. or March for fertilizing.