Different perennials need to be divided at different times of the year, as a general rule of thumb, if it flowers in the spring divide in the fall, if it flowers in the fall, divide in the spring.
Start by digging up the root ball of your plant and transferring it to a tarp or another work surface to divide.
Wet the roots to remove excess soil so you can see where to divide. Leave a good root network for each section you're separating.
If the root system on your plant is too large to completely remove, dig around a portion of the plant, and work a section at a time to loosen and remove it from the remainder of the plant.
When replanting divided plants, make sure that you work in some compost or fertilizer into the soil to give it a jump start into re-growing.
Depending on how tight your root ball is you may need to use a garden knife or a spade to separate the plant.
Easy division to multiply your landscaping. I'm Mrs. Fixit and it's just that simple!