I always jokingly tell people that the best time to divide perennials is when they have the time to do so! While this idea works for most of our perennials most of the time, there are, indeed, optimal times to divide various plants. Generally, divide plants when they are dormant or close to dormancy. In our area, this would be fall through spring, whenever the soil can be worked. Avoid dividing in extreme hot or cold weather and in very dry and wet conditions. Plants that have tubers and fleshy roots, such as iris and peonies as well as other spring bloomers, may appreciate being divided more in the late summer or early fall timeframe—after they bloom—to give them time to become reestablished and maximize their bloom the following spring.

Different plants have different requirements for how often they will need to be divided. For example, a peony would not necessarily ever need to be divided. On the other hand, many plants, such hostas, daylilies, and chrysanthemums, could benefit from division every year or two. Plants will sometimes give you signs that they are in need of division. They will start to die back in the center, flower less freely, or simply outgrow their space.

Until you become comfortable with the needs of your plants, it may worthwhile to double check a garden encyclopedia at the library or call your county extension office if you have questions about dividing a particular plant. You can also check Web sites for information.

Fine Gardening has an excellent article on their Web site that goes in to more depth about this subject and has a link site within the article that covers how best to divide individual plants. For this article, go to http://www.taunton.com/finegardening/pages/g00021.asp