Fall is the perfect time to divide your perennials. Here's how to do it right.

Fall is a great time to divide many overgrown perennials.

Generally speaking, summer blooming perennials are divided in the fall and fall bloomers are divided in the spring. Dividing perennials when they are not blooming causes less stress to plants. The less stressed the plant, the more likely it will survive division, especially with some finicky perennials.

Most perennials are divided every three to five years. Some may wait for eight to 10 years and others resent being divided and will let you know by refusing to bloom or getting the "up-and-died" disease.

Perennials often send signals to let you know when they need dividing: reduced flowering with smaller blooms; center of the plant dies out leaving green growth only on the edges; plant loses vigor; plant needs staking due to lodging. Otherwise, if the perennial is growing and blooming well it should be left alone, unless more plants are wanted or the plant is over growing its bounds.

Before you rush out to divide your perennials, it is important that you first prepare the plant.

• Water plants to be divided one or two days before you plan to do the work.

• Prune stems and foliage to six inches from the ground to ease division and reduce moisture loss.

• Select a cloudy day, ideally with several days of light rain forecasted, to reduce heat stress to your uprooted perennials.

• Using a sharp pointed shovel or spading fork, dig down deep on all sides of the plant and about four to six inches away from the plant.

• Lift the entire clump and shake or hose off loose soil.  Remove the dead leaves and stems, trim off any damaged roots, and discard the old, dead center of the plant. This will help clean the plant and expose the roots.

Plants are divided according to their specific root system. The list below includes many common perennials, their type of root systems, and steps to division:

Spreading: (Astilbe, Beebalm, Bellflower, Black-eyed Susan, Cranesbill, Coreopsis, Garden Plox, Lamb’s Ear, Purple Cone-Flower, Yarrow) These plants have a matted root system with no distinct pattern. They have a tendency to die in the center when overgrown and some can become invasive. Divide these plants into clumps of three to five vigorous shoots each. Roots can usually be cut apart with a knife but thick intertwined roots may require forceful separation.

Clumping: (Daylily, Hosta, Lily of the Nile, Red-hot-poker) These plants originate from a central clump, many have thick, fleshy roots. It is often necessary to cut through the crowns of these perennials with a sharp knife.  Keep at least one bud with each division; leave several buds for larger plants.

Rhizome: (Bearded Iris, Blackberry Lily) Rhizomes are stems that grow horizontally at or above the soil level.  When dividing rhizomes, cut and discard the oldest sections and those damaged by disease or insects. In the case of iris, your new division should have a few inches of rhizome and one fan of leaves.  Replant with the top of the rhizome just showing above soil level.

Keep your new divisions moist until they are planted. Replant divisions at the same depth they were originally and tamp the soil around the roots to remove air pockets.  Fall can sometimes be dry, so be generous with the water.

Adding mulch to garden beds is always a good idea and with new plants, it may give them some extra survival insurance this winter. A light application of 10-10-10 will also help give the roots of your new transplants a healthy start.

Dividing will rejuvenate old plants and keep them vigorous and blooming freely. Dividing perennials is an easy and inexpensive way to gain additional plants for your garden or to share.

However, remember that not all plants appreciate division. Butterfly weed, euphorbias, baby’s breath, false indigo, columbines, rosemary, candytuft, lavender cotton, and rosemary are a few that are best left alone.

The work you put in this fall will pay off next spring.

P. Andrew Rideout is the UK Extension Agent for Horticulture and can be reached at [email protected].

This article originally appeared on Evansville Courier & Press: How do I divide perennials?