Master Gardener - Dividing perennials multiplies landscape plantings

Published: Thursday, February 13, 2014 at 05:05 PM.

Buying enough plants to fill all the empty spots in your landscape can quickly become expensive.  One way to minimize the number of plants you need to buy over the long term is to purchase perennials. Perennial plants return from the same roots each year. Most multiply and spread, and can be divided every few years to make new plants. Most perennials are not temperamental and, if properly divided, will fare well whether they are divided in spring or fall. 

When to divide perennials

A good rule of thumb for dividing perennials is to do so in the season opposite of when they flower. So spring and early summer bloomers such as Coreopsis and Iris are best divided in fall, while late summer and fall bloomers such as Mexican bush sage and Joe Pye weed are best divided in early spring. The idea behind this is that the new plants will be able to put all of their energy into root and leaf production, rather than flowering, and therefore have an easier time becoming established. Spring division is ideally done as soon as the new growth emerges, which for many perennials begins in mid February or early March. 

How often to divide perennials

Perennial plants are healthiest and most productive when they have room to spread.  Most perennials should be divided every three to five years. Some vigorous perennials like daylilies and black-eyed Susans (Rudbeckia) may need to be divided every other year or they may crowd themselves into non-flowering clumps of leaves and roots.

To determine if your perennials are ready to divide, take a look at the size of the clump and amount of room they have available to grow. Most perennials will spread and run out of growing room over time. When this happens it is time to divide. Some plants resent being divided and should be left alone if possible. These include butterfly weed (Asclepias), euphorbias, Japanese anemones, false indigo (Baptisia), columbines (Aquilegia), as well as Lenten and Christmas roses (Helleborus). 

How to divide perennials

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