Transplanting shrubs, perennials

Email the author | Follow on Twitter
on September 04, 2008 at 10:26 AM, updated September 04, 2008 at 10:34 AM
A clump of purple coneflowers being pulled apart to make two plants.

Q: Is there a general rule about moving shrubs and perennials. Can some plants never be moved once they take root? Is there a time restraint for most plants? I know that some clumping plants do well with being broken and moved. I also heard that yuccas shouldn't be moved. I'm new to gardening so any info would be welcome!

A: Most plants move pretty well if you get sufficient roots, transplant when conditions are right and keep the moved plant watered after the transplant as you would with a new plant. Younger and newly planted plants move better than older, long-established ones.

One sign of a veteran gardener is that he/she has moved just about every plant in the garden two or three times. These people have learned that with a little plant-care knowledge, transplant success rates are pretty high. Beginner gardeners are more afraid that they'll kill a plant if they dig it up.

In general, shrubs are transplanted whole by digging up the entire root ball and moving it to the same depth in a new location. Most perennials can be broken apart or divided into smaller pieces, which is a main way new perennials are propagated. As you suspect, spreaders and clumpers divide better than things like yucca, baptisia, sea holly and gas plant, which have deep central tap roots.

The best two times to move plants is early spring before it gets hot and dry (i.e. late March to mid-May) and between Labor Day and October when it's getting cooler and damper again but when the soil is still warm enough to support root growth.

Some advocate using "root starter" products to aid planting and transplanting, but I think these have a marginal benefit at best. Good soil and adequate water are far more important, in my opinion. I seldom use any fertilizer during plant moves... just good, ol' compost mixed into the loosened soil at the new site.

If you must add something to sleep well at night, add a scattering of balanced, granular, organic fertilizer or a little mycorrhizal fungi (granular "root-helpers," not fertilizers, that are sold now in most garden centers alongside the fertilizers).

I can't really generalize much more than that because there are plenty of peculiarities from plant to plant. For instance, asters flower best when divided every two or three years. Hostas usually do fine even if they're never divided. Fall bloomers such as sedum and mums are best transplanted before new growth begins in spring. Spring bloomers such as foamflowers and dianthus are better moved in fall when not in bloom. Bearded iris are best split a month or two after they bloom, which is early summer, etc., etc.

An excellent book that details when and how to transplant/divide perennials is Tracy DiSabato-Aust's "The Well-Tended Perennial Garden" (Timber Press, $34.95 hardback, 2006).