Dividing is done for several reasons: Often, older perennials grow poorly and dividing reinvigorates them. Dividing also keeps perennials from overgrowing or encroaching on neighboring plants. You can divide plants to increase your plant stock; you may want more of that plant elsewhere in your garden. Finally, dividing allows you to share your plants with a gardening friend!
To divide a perennial dig it up as if you are transplanting it (refer to the lesson 8 transplanting for details). Shake off excess dirt to expose the roots and separate the plant and roots into sections using either a serrated knife or your hands. If the perennial has a large tuberous root (called a crown) you can use a knife to slice off divisions of the root. Replant the sections you want to keep, treating them as if they were new plants.
• Dividing is best done in the Spring or early Fall.
• If the plant is in bloom, wait until after it has finished blooming to divide it.