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Gardening comes with many silly rules. The one I hate most says you can only divide perennials in spring, when plants are starting to grow, and in fall, when they are mature.

When it comes to dividing, I only have two rules: Don't do it if frost is expected in the next week, and don't do it during a heat wave. Otherwise, knock yourself out.

There are good reasons for splitting up plants at this time of year.

Some die out in the middle, others get too big for their location, still others look miserable and stop blooming.

At this point you can probably see what holes in the garden need to be filled. Rather than hitting the garden centre, it's possible to create new and interesting combinations out of what you already have.

Or maybe you need to keep a bloated plant under control by getting rid of the excess growth.

The other day a friend and I whacked gigantic hostas in halves and thirds. Hostas are hard to divide in full summer growth, but what a huge difference it makes in how they look the rest of the year.

They tend to sulk for a couple of days, but bounce back amazingly well. The leaves become richer and silkier. The new plants you create by division are large and will quickly flourish in a new location.

THE DIGGING

To divide a big, heavy plant, use a transplanting spade to lift it out of the ground. Get a garden spade with a flat sharp edge and whack the plant in the middle as hard as you can. Choke back all those empathetic feelings if leaves break off - put them in a vase and they'll look fabulous, especially hostas.

THE TRANSPLANT

Make a hole exactly the same size as the chunk you are taking out of the ground. Fill it with water to ensure the drainage is good, plop the division into place and backfill.

THE FOLLOW-UP CARE

Don't amend the soil. This is where the plant has to live, so tough love is the order of the day.

Water thoroughly so it flows below the root system, then add compost around the top of the soil. For the next two weeks keep your eye on the new plant and make sure it's watered deeply.

THE REMAINS

Put one of the pieces you have chopped up back into its original spot and treat it as you would a new plant - with lots of TLC.

Give your plant divisions the same care and they'll reward you with vigour and long life.

Garden rules are made to be broken. Don't be intimidated by the strictures - use common sense, buy extremely sharp instruments of division and you'll have happy plants.

Marjorie Harris is editor-at-large of Gardening Life magazine; her most recent book is How to Make a Garden: The 7 Essential Steps for the Canadian Gardener.*****

Divide and conquer

Irises must be divided when the plant gets a big hole in the middle. Make sure you whack them into parts with a sharp, clean, old butcher or bread knife. Reset them in the soil so that some of the lumpy corm shows at the surface.

When perennials such as shasta daisies or other clumping plants get overwhelming, have a go at them with a butcher knife or even two garden forks to push them apart.

Jack-in-the-pulpit is one of the spring plants that grows quickly, spreads by rhizomes and divides nicely. Find out where the roots are heading, pick a spot and make a fast, clean cut.

Peonies are an exception. Wait until autumn, when the foliage is mushy, to divide them.

Marjorie Harris

http://www.marjorieharris.com