Fall is the best time to divide spring and summer blooming perennials that are overcrowded, dead in the center, failing to flower or flopping open. Wait until spring to dig and divide fall or summer blooming perennials that were not moved the previous fall.
These are guidelines that increase success, but most gardeners have found that the best time to divide is when you have the time and can provide good, proper post-transplanting care.
Use a sharp-edged shovel to dig the perennial, roots and all, out of the ground. Lift the clump out of the soil and use a linoleum, garden knife or drywall saw to cut the plant into smaller sections.
Some gardeners prefer to use two garden forks placed back to back in the center of the clump and then pry the perennial apart into two pieces. Continue the process until the desired size and number of divisions is achieved.
Discard and compost the dead center. Divide the remaining plant into four, six or eight pieces. The smaller the divisions, the longer it will take for the plants to reach mature size. Larger divisions may quickly grow, fill the space and need to be divided sooner.
You can plant one of the divisions back into its original location. Use the others to fill voids, expand existing gardens or start a new bed or border. Just make sure to match the plant with its desired growing conditions.
No matter how you plan on using the divisions, you should prepare the soil first. Add compost, peat moss or other organic matter to the top eight to 12 inches of soil. Plant the divisions at the same depth they were growing in the garden. Water thoroughly at planting and throughout the fall or subsequent growing season whenever the top few inches of soil starts to dry. Spread a layer of shredded leaves, evergreen needles or other organic mulch over the soil surface. Be careful not to bury the stems. Mulch helps moderate soil temperatures, conserves moisture, suppresses weeds and improves the soil as it breaks down.
Regular dividing can also help eliminate other garden tasks like deadheading, staking and replacement. Divide repeat blooming daylilies every few years to keep them blooming throughout the season. Do the same for threadleaf coreopsis.
Divide asters every year or two in the spring to keep them vigorous and control their spread as needed. Increase the vigor and compactness of Shasta daisies by dividing them every two to three years.
Peonies, on the other hand, seldom need dividing. They can remain in the ground undisturbed and blooming profusely for decades. Fall is the time to dig and divide peonies if you need to move or want to divide them to make more plants (propagate).
Don't be alarmed if your peony or other perennials fail to bloom the year after transplanting. The transplant often spends the first year establishing a healthy root system instead of flowering. Just be patient and you will be rewarded with flowers the following year.
Take advantage of the warm soil and cool air of fall to dig, divide and transplant overcrowded and struggling perennials. Your efforts will be rewarded with better looking and more floriferous gardens.
Melinda Myers has written more than 20 gardening books, including "Small Space Gardening." She hosts The Great Courses "How to Grow Anything" DVD series and the nationally syndicated Melinda’s Garden Moment TV and radio segments. Myers’ website, MelindaMyers.com, features gardening videos, podcasts, audio tips and monthly gardening checklists.