Late summer and early fall are the best times to divide many perennials, including peonies, irises, daisies and dozens of others. In general: divide spring and summer-flowering perennials in late summer and fall, and late-summer- and fall-flowering perennials in spring.
Preparing to divide hostas
© Jo Ellen Meyers Sharp
In fall, the temperatures have cooled down and the soil is still warm and moderately moist, which encourage a plant’s roots to develop. It’s best to give transplanted perennials four to six weeks to get established in their new sites before the ground freezes.
Division is about the easiest way to get more of the perennials you like. With division, you break up one large clump into smaller clumps. These divisions will be identical to the parent plant. Keep in mind that it may take two or three years before these transplants bloom. The larger the transplant, the sooner it will bloom.
Prime candidates for divisions are plants that have grown too thick or have a dead zone in the middle, and those that have fewer flowers than they used to or have stopped flowering altogether.
Here are some tips:
- Prepare the new planting areas before digging the plants for division. Dig a hole twice the width of the segment’s root ball and about the same depth. Mix a trowelful of compost, rotted manure or other organic matter in the planting hole. Do not add fertilizer to the hole.
- Make sure the plants to be divided are mature. Immature plants will have their development disrupted by dividing them.
- Make sure plants are well watered a day or two before beginning the task. Moist — not wet — soil makes it easier to dig the plants and divide the clumps.
- If possible, pick a cool, overcast day for the job. This kind of weather tends to be less stressful on plants than a hot, sunny day.
- With a spade or a garden fork, carefully dig the clump from the ground.
- Examine the clump to identify natural gaps in the growth where sections can be split. Each division should have top growth and roots.
- There are several tools you can use to divide plants. The sharp blade of a spade works well on large, dense clumps. You can also use two garden forks to separate clumps, a technique that works well with daylilies. Or, you can slice through a clump with a bread knife or other serrated blade, a method that works well with hostas.
- Do not remove soil from the severed segments.
- Protect the segments from the hot sun by covering them with a moistened cloth or newspapers to prevent them from drying out until you can transplant them to their new location.
- Plant the segments and water well. New plants need about 1 inch of water every week, either by rainfall or from the garden hose. Continue to water the new transplants as needed through fall and during dry times the following year until they are established.
- Add a layer of Preen Mulch with Extended Control Weed Preventer to prevent weeds for six months, to retain moisture and moderate soil temperature while adding beauty to the landscape. The high-quality hardwood, pine or cypress mulches are treated with two long-lasting preemergent herbicides. These mulches come in several colors including Russet Red, Midnight Black and Chestnut Brown. One 2- cubic-foot bag covers 12 square feet. Preen Mulch with Extended Control Weed Preventer is available at Lowe’s and other select lawn and garden centers.