Dividing and moving perennials is easier than most people think, and in many cases, your plants will be the happier for it.
Besides moving plants for aesthetic reasons, it is often desirable to move plants as the garden matures, to give them more air and light.
Splitting plants will also encourage better blooming for many species, such as day lilies, which tend to get crowded over the years and produce more foliage than flowers.
All perennial flowers are a pretty safe bet to divide, as are biennials. As long as they are given the suitable location, mulch and fertile soil any plant reasonably deserves, they will put down good roots and make themselves right at home in the 6 to 10 weeks we have before winter weather sets in. Be sure to cut off all flowers and seed heads so that the plants can truly put their energy into strong, new roots and not into setting seeds. They cannot do both.
Many shrubs, including azaleas, boxwoods and junipers, as well as small trees, also do well with early fall planting or transplanting. (Their prime time for transplanting is in the early spring.) Their root growth is less vigorous in the fall, so make sure the soil is very well prepared for them and make your planting hole extra generous.
First, prepare soil beds well and add compost if available. While you are digging, it is a good idea to add some bone meal, about a half-cup per plant, to help get the plant started. Go easy on the fertilizer, and beware of fertilizers with a high nitrogen content; you do not want to stimulate new growth, which will sap the plant's energy and weaken it. A handful or two of bone meal is usually sufficient. Bone meal will encourage strong root growth, and a tablespoon of Epsom salts will aid flower-bud formation for next year.
Dig congested plants out in a clump, or their existing group structure, and lay the clump aside. If you are not going to work with it immediately, water it and cover it with a tarpaulin or newspapers, so it will not dry out.
Many plants can be separated easily by hand, just by shaking or gently breaking them apart. Irises and day lilies, with their knobby, segmented roots or rhizomes usually fall into this category.
Other perennials come out in basketball-size masses that look like they intend to stay together. If the plant you are working with does not come apart readily, you can split it into fist- to grapefruit-size clumps for replanting in one of several ways. One is to use a pair of garden forks to gently pry apart the roots; this works well on things like daisies, herbs and purple coneflowers.
If the root structure is too dense for that, say with hostas or ornamental grasses, you can use a large, sharp kitchen knife to cut the plant into chunks. This sounds more grisly than it is: The trick is to look for natural divisions in the clump, and to make sure the cut is clean. The resulting clumps should be about the size of a grapefruit or softball, and should be spaced 18 to 24 inches apart when replanted.
If you are transplanting from containers into the garden, remember to loosen the roots of the plants gently as they come out of the pot. This is especially important if the roots have become root-bound, tightly circling the inside of the pot. In this case, it is imperative to tease the root ball apart, or in some instances even cut the outer roots at 6-inch intervals with a knife to free them up. Otherwise, the roots will continue to grow round and round and may eventually strangle the plant; at the very least, it will not make good growth.
Remember to water the new transplants regularly. The soil should not dry out. If the plant is an evergreen, use an anti-dessicant, such as Wilt-Pruf, to reduce stress from moisture loss and wind damage during the coming winter.
Do stake plants that threaten to flop over and help them stay anchored while the new roots grow.
For more information
Most general gardening books will have a chapter on transplanting.
* A special-interest publication, Planting and Transplanting (Plants and Gardens, Vol. 38, No. 1), by James Cross, Brooklyn Botanic Garden, 1989, is out of print, but available through Amazon.com
A useful Web site for those transplanting small trees and shrubs:
* www.griffin.peachnet. edu / ga / cobb / Horticulture /
Factsheets / Transplant / transplant.htm