Spring is a great time to divide many of our favorite herbaceous garden perennials. The plants are small, easy to handle and they have the entire growing season to get re-established in your garden. But how do you know how often to divide perennials.
The term “perennial” literally means to last or exist for a long time and to be enduring or continually recurring. A perennial plant re-grows year after year from the same root. Some perennial plants are very long-lived like an oak tree which others are short-lived like some of the newer coneflower cultivars.
Dividing perennials or “division” is a form of propagation: you are creating multiple plants from a single plant. Some plants like Heuchera, coral bells, are very easy to divide. The plant crowns are right at the surface of the soil and small plants, called ‘offsets’, develop from the larger main plant. Other plants like Hosta and ornamental grasses have dense roots that require a sharp knife, garden fork, or even an axe to cut apart.
Division also promotes plant health and can rejuvenate a plant. A perennial should be divided when it dies out in the middle (the oldest part) of the plant, produces smaller flowers or leaves, and blooms less.
Dividing perennials is also a good idea if plants have become crowded as it increases air and light around plants which can increase blooming as well as reduce disease and insect pests.
For a great guide to knowing when to divide those perennials check out this factsheet: https://extension.psu.edu/dividing-perennials