Dividing Perennials in Fall

Perennials are wonderful plants. They come back every year, and each one blooms on a reliable schedule all its own, allowing a gardener to mix and match colors, textures and bloom times. As perennials make themselves comfortable in a garden, they may need to be divided. Dividing a perennial plant means to cut it into pieces and replant each piece, either in the same or different locations.

Perennial plants can be divided for many reasons. Competition and overcrowding can weaken a plant and prevent it from blooming to its full potential. Dividing a beloved plant allows the gardener to create drifts throughout the bed, and helps fill in new beds. Dividing is also a great way to share plants with friends and neighbors, whether they really want them or not. And if there are simply too many, divisions can be sold at yard sales and roadside stands, or donated to a local garden club.

Fall is a great time of year to divide spring and summer flowering perennials, such as daylilies, bee balm, bearded or Siberian iris, peony, astilbe, poppies or daisies. Some perennials that bloom in late summer, such as black-eyed Susan, chrysanthemum, and aster will also benefit from dividing in fall. Each division will get a head start over the winter and reward you with renewed vigor in spring.

Nosey Rosie. Top left.

Choose a cool, cloudy or overcast day to divide and replant, just before a rainy spell is predicted if possible. Cool temperatures and gentle moisture will help the plants recover from the stress of dividing and replanting. If you do work in the sunshine, shade the plants with a large cardboard box or plastic container after replanting to prevent wilting. Water each plant to be divided and let it soak in while gathering tools. Gather a shovel, spade, or spading fork, heavy-duty knife or pruning saw, pruners, a tarp or old tablecloth, water, and mulch. If you have compost or other organic matter, use it to mix into the soil that is used to replant the divisions.

If possible, select locations for the new plants and dig the planting holes before dividing the original clump. This will minimize the time the plants spend with their roots exposed. Dig the hole slightly wider than the division will be to allow space for the new plant to spread out its roots.

Divide large, established, healthy plants. Use a shovel or spading fork to dig deeply around the entire plant. Keep as much of the root system intact as possible. If working with a very large clump, force the shovel under the root ball to loosen it before you lift the plant. Or, insert a spading fork at an angle several inches outside the perimeter of the top growth. Lift gently until the clump comes free from the soil. A spading fork won't damage roots as much as a shovel, but certain plants with very tough roots such as daylilies will not be harmed if they are cut with a shovel.

Lift the plant out of ground and shake off loose soil. Each division should have two to five strong shoots with ample roots attached. Set the plant down on a tarp or old tablecloth on a flat surface, and divide it into smaller clumps either by hand, or with a knife or spade. Roots of older or woody clumps can be so tough that you'll need to cut them with a heavy-duty knife, or split them with a sharp spade. Plants like hosta and coral bells can have very thick, dense crowns. Split them with an ax once they are out of the ground – they can take it.

Remove any dead, damaged or diseased areas of the plant. If the foliage is too lush to be supported by the new root ball, cut the leaves back to half the height of the original clump. Set plants out at their original depth. Planting too deeply can invite crown rot, while not planting deeply enough can cause the plant to heave out of the ground and die over the winter. One division can be planted back into the original hole. Fill in around the plant with soil/compost mixture and tamp down lightly.

Water each division. After the soil has dried some, lay an inch or two of mulch to keep soil from drying out and to protect the plant's root system. Use shredded leaves, wood chips, or small evergreen boughs. Keep the soil moist for a few weeks until your new plant becomes established. Wait until spring before adding fertilizer.

Be sure to replant divided perennials promptly so roots don't dry out. If the new plants can not go into the ground immediately, plant them in pots, water them, and set them in a shady area until ready to go into the ground. If the plants must be left in the pots over the winter, bury the pots up to the soil line to protect the roots. The divisions should return in spring, ready for their new homes.

If you get a perennial plant from another gardener, check it for weeds and for pests like slugs, grubs and aphids. Do this after your friend has gone home. Feel free to keep any stowaway earthworms.

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