Dividing Perennials

When to Divide

In northern climates, most perennials are best divided in early spring, after the soil has warmed up and growth has begun. Fall is also a good time to divide many perennials, but be sure to do it at least a month before the ground freezes, so the plants have time to get established. In cold climates, it helps to mulch newly divided plants over the winter to protect them from damage caused by fluctuating temperatures. See What is Mulch.

A basic rule of thumb is that if a plant blooms early in the season, divide it late in the season, and if it blooms late, divide early. Avoid dividing perennials when they are in bloom. Some especially tough perennials, such as hosta and daylilies, can be divided anytime. Just try to pick a cool, cloudy day and keep plants well watered.

In climates with mild winters and hot summers, fall may be the best time for dividing perennials. This allows the plant to get established over the mild winter.

Try not to do divide on hot, sunny days. Dividing on a cool, cloudy day, or even during light rain, will help minimize shock to the plant.

How to Divide

It may help to water the plants a day ahead of time to make it easier to dig them out of the ground. With a sharp spade or shovel, dig up the entire clump with as many roots as possible. Cut the clump into several sections with a shovel or knife. It’s ok if you damage some of the new growth, but make sure each division has several shoots or stems.

If the plant you are dividing is very large and you can’t dig up the whole clump, you may simply use a shovel to slice down and remove sections of the plant, leaving the rest of it intact in the ground.

Plant divisions as soon as possible and don’t allow them to dry out. To keep plants moist until they are planted, set them in the shade or in a pail of water. Remove any broken or dead leaves, stems, and roots with a sharp knife or pruners. Replant divisions at the same depth of the original plant, gently pack soil around the roots, and water well.

You will need to keep newly planted divisions well watered until their roots are established.

Dividing Perennials that Grow from Rhizomes

Dividing plants that grow from rhizomes, such as iris and cannas, requires a little more finesse than dividing other plants. Rhizomes are thick, fleshy stems that grow horizontally just beneath the surface of the soil.

Carefully lift the entire clump of rhizomes out of the ground and shake or wash away the soil that clings to them. The clump will consist of older, spongy rhizomes and lighter-colored young ones growing from their sides. Cut the young rhizomes away from the older segments with a sharp knife. Replant only plump and healthy-looking rhizomes and discard those that are old, withered, or diseased. The top of the rhizome should just show above soil level. To reduce moisture loss, trim the leaves of the plant by about two thirds.

Deciding When to Divide

How often to divide your perennials will depend on the plant and your conditions. If an established perennial produces fewer or smaller flowers than normal or the center of the plant looks hollow or dead, it may benefit from division. Plants that are growing and blooming well should be left alone, unless your goal is simply to make more plants.

Some plants don't need dividing and resent having their roots disturbed. These include monkshood (Aconitum), false indigo (Baptisia), bleeding heart (Dicentra), lupine (Lupinus), peony (Paeonia), and poppy (Papaver).