How to divide your perennials

To keep perennial plants performing at their peak, it is necessary to lift and divide most of them every few years.  Both spring and autumn are good times to do this. You’ll end up with more plants than you started with, so begin a new flower bed or give the extras to a friend, local horticultural societies, or schools. As a last resort, the discards can go on the compost.

Many gardeners prefer to divide their crowded perennials in the fall. As in so much of Canadian gardening, when you should do it depends on your hardiness zone. You have to be sure the plants will have enough time to get their roots growing well in the new location and that the new growth is not too tender to survive the winter.  My rule of thumb; allow at least 6 weeks in the new location before the first hard frost.

Why and how to divide your perennials

Plants are usually divided for one or two reasons. Firstly, the plant has outgrown its given space; or secondly it is fully mature and needs rejuvenating. This becomes noticeable when the centre of the plant begins to deteriorate.

Identify the plants that are overgrown and dig them up using a garden fork. I like using a good quality garden fork as it damages fewer roots. If you only have a spade or shovel, they will work too. Make sure that you sharpen your tools with a grinder or use a gardener’s file.

Drive the fork into the ground around the entire plant, without pushing down on it too much. The idea is to cut some of the roots before levering the root mass out of the ground. After you have completed the circle one time without using leverage, do it again only this time push down on the fork/spade ripping and tearing roots as you go. By the time you have completed your second pass around the plant, chances are pretty good it will lift easily out of the ground.

Take your time. Once you have the plant – roots and all – out of the ground, you have a decision to make; how many divisions will you make?

After I have divided the plant in ½ , I do it again, dividing it into quarters. If it is a really big plant you can divide it again. Now you have a bunch of wedges sitting on the ground ready to plant. If you can’t plant them right away, place them in a shady spot and water them thoroughly. Keep them wet until you can plant them or give them away.

When you plant your new divisions, use good quality soil (triple mix works nicely) and water them in well.

Dividing hosta

What perennials are suitable for dividing?

-           Mature plants

-           Fibrous or fleshy roots systems

-           Out of bloom and dormant

If you’re feeling nervous about lifting and dividing, these plants are easily divided: yarrow, astilbe, bellflower, coreopsis, evening primrose, phlox, veronicas, and the extremely popular hosta.

Mark Cullen appears on Canada AM every Wednesday morning at 8:40.  He is the Lawn and Garden expert for Home Hardware.  Sign up for his free monthly newsletter at www.markcullen.com.