It’s always near the top of any list of fall gardening chores: Divide perennials.

Why? Large clumping plants — such as cannas, black-eyed Susans and day lilies — end up competing with one another and other things in the garden, meaning fewer blooms.

Plus, when there’s more room between plants, there’s better air flow — and less chance for disease to spread.

An added benefit? Dividing perennials gives you more plants to share with friends and neighbors.

Why in the fall? Because plants tend to transplant better when the weather is cool. They’ll get stressed any time you transplant them, but doing it when it’s too hot or too cold can be too tough for them. Transplanting in the fall gives the plants time for their roots to grow before the winter sets in.

How often? It depends on the plant. Think about dividing them when they start to look crowded, or start infringing on other plants in the garden, or start to die off in the middle.

As a rule of thumb, every two to three years is a good schedule to divide most perennials.

Exactly what does it mean when you hear “divide” perennials?

We asked Andy Cabe, curator at Riverbanks Zoo and Garden in Columbia, S.C., to demonstrate the best way to do it.

For this example, he divided an amacrinum, a late summer/early fall bloomer that’s a cross between an amaryllis species and a crinum.

To start, he used a shovel to loosen the soil around the perimeter of the plant. Because amacrinums have large bulbs, he made sure he started digging far enough outside a clump so he didn’t slice off any of the root ball.

Once you remove the plant and its roots from the soil, it’s time to divide it. You can do that several ways, depending on the type of plant you’re working with. A day lily’s roots often are tangled, so you can use a garden fork to pull the roots apart and break them into separate plants. Hibiscus can be cut using a flat shovel.

With bulbs, you need to be sure to dig deep enough so you don’t damage the basal plate, the area at the bottom of the bulb that holds the scales together and produces roots. You can divide one bulb into as many pieces as you like as long as you have a piece of the basal plate on each. Some people use scissors, knives, shovels or simply their hands to pull apart the roots and divide the perennials.

The next step is to cut off the old flower stalk, making it easier to handle. Doing that also compensates the plant for losing some of its roots, meaning the stress of transplanting will be eased.

“A lot of plants can go into transplant shock,” Cabe said. “If you cut the foliage and if you (divide the plants) at the right time of year, you can reduce the amount of transplant shock.”