Dividing Perennials


by Karen Weiland, Advanced Master Gardener




One of the maintenance chores of growing perennials is that of dividing them when needed.  There is no set time to do it.  Some may need it every 3 – 5 years, some 8 – 10 years and some would rather not have you touch them at all.

Perennials will let you know when they need dividing.  Some signals to look for are:  flowering has declined and the flowers are getting smaller, the center of the plant dies out leaving a hole with all the growth around the outside, the plant starts to flop over and needs staking or the plant just has lost it’s vigor.  Spring is usually the best time for division to take place but some plants such as Peony, Poppy and Iris are best divided in late summer to early fall.  Perennials that show signs of going dormant with browning foliage can also be moved or divided as well. It is best to avoid moving or dividing perennials if they are in bloom or about to bloom.  Wait a few weeks until after they have put on their show.

The process of dividing begins with preparing the new planting site before lifting the plant to be divided.  To lift a perennial with little root damage, begin digging at its drip line.  The roots will generally extend that far, so digging there will keep most of the roots intact.  Dig around the plant to be divided, then lift the entire root clump out of the ground.  It might help you to tie the stems together before lifting the plant to minimize damage to the leaves. Cut the clump up using a spade or a sharp, serrated gardening knife (the knife is by far my choice).  Throw away the dead center if there is some, and any damaged roots.    After they have been replanted, mulch and water them well and keep them watered throughout the fall to prevent drying.  Mulch up to the crowns but do not bury them. I like to use a root stimulator product when doing any transplanting or planting of new stock.  This stuff is fantastic!

The root system of perennials will be better able to withstand the winter if they are transplanted in late summer to early fall.  Late fall plantings can sometimes result in frost heaving and damage or loss of the plant because they do not have a sufficient root system to anchor them into the soil.

I prefer to leave many of my perennials standing during the winter months rather than cutting them back.  Many perennials have seed heads that act a source of food for birds and the stem bunch can be a place for some birds to hide.  Mums benefit a great deal by leaving the stems uncut as leaves and snow will accumulate in them over the winter and insulate the crown.  Uncut stems of perennials will help to identify where the plant is so there will be no accidental digging taking place in that spot in the spring.  If the perennial was bothered by some foliage disease during the growing season then it would be a good idea to remove the old foliage to reduce the amount of reinfestation in the.next years’ growth.

If you are going to cut your perennials down for the winter, do so after they have gone dormant.  This usually happens after there have been several hard frosts.  Cut the plants down to about 3 inches from the crown.  Cutting too close can result in injury over the winter because for some plants their next year’s growth buds are right at the surface or higher and not below the soil.


As always, Happy Gardening!


More information about gardening and related subjects is available online at http://www.hort.purdue.edu/ext/garden_pubs.html

or http://web.extension.uiuc.edu/state.  The Purdue University Cooperative Extension Service can be reached at 499-6334 in LaGrange Co., 636-2111 in Noble Co., 925-2562 in DeKalb Co. and 668-1000 in Steuben Co.