The Basics of Dividing Perennials
Haliburton County Master Gardener
Many new gardeners wonder not only when but how to divide perennials. A little bit scary as you never want to kill the plant but would love to have another specimen for a new bed or perhaps the plant is brown in the centre and blooming has tailed off to almost nothing. While there are several species that have a preference for when to divide, most perennials can be divided at any time - with the right tender loving care.
So why would you want to divide a perennial? Many perennials die back in the centre as the roots in this area are so dense they cannot get sufficient moisture and nutrients. These plants along with plants that you smaller and fewer blooms need to be divided. Other plants are very fast growers and soon outgrow the designated space in the garden. Overcrowded flower beds means that plants compete for water and nutrients and reduces air circulation. Reduced air circulation in the beds may encourage disease. Perennial division will keep those gardens neat, healthy and in peak bloom. You may also find that weeds have taken over a perennial or two. When dividing you can remove many of these weed roots and replant a smaller but healthy plant.
Generally speaking plants that flower mid-June and later should be divided in spring and plants that flower early to mid-spring can be divided in the fall. There are always exceptions to any rule of thumb and plant division is no different. For example peonies are best divided in the fall, irises in July and Iceland poppies in August. Spring division gives the plant a full growing season in which to recover from division.
Any time you dig up or disturb the roots of plants they are under stress, reducing their ability to take up water and nutrients. Watering the plants that are ready for division the day before will help to reduce this stress. When dividing there are some key steps.