Late summer and early fall is an ideal time to divide perennials. As you walk through your garden notice those plants that have outgrown their alloted space, are centering out in the center or are just not blooming very well any more. These are all signs that they need to be divided. Dividing plants will rejuvenate them and encourage more blooms. The beauty of perennial divisions is you can share your plants with your friends or if you have a large yard or are opening up new beds, you can move them to a new location. New plants for free!
Some perennials do not like to be divided and others require it only after several years in the ground. Most fall somewhere in between. A few that do not like to be disturbed are bleeding hearts, false indigo, gas plant, lupine, oriental poppy, christmas rose, columbine and foxtail lily.
There are books written about how to divide plants but for most of us a few simple guidlines will do. Allow your divisons about 4 to 6 weeks before the first frost date to get established so they will survive the upcoming winter. Water the plant well and divide if possible on a cool day or later in the day if it is still quite hot. Using a spade or fork dig out the entire plant making sure you dig wide enough to take out the entire root system.
Shake off the soil and snip off any dead growth and tall stems. If the plant is old with a woody center cut out that portion and save the new strong roots and crown around the edges. If the plant has a cluster of crowns gently pull them apart making sure each division has a growth bud . Replant your divisions right away in a prepared planting hole. Large masses of crowns separate easily using 2 garen forks pushed back to back in the center of the clump. Rock the handles back and forth and the crowns will slowly separate. Grasses may require a knife or ax to separate into divisions.
Once you have done a few division of plants you will get a feel of how the roots of various plants grow together. As long as each new piece has part of the crown or a growth bud and some healthy new roots you should be fine. Practice makes perfect.