By Emma Murphy, Master Gardener

(This blog entry builds on last week’s excellent post by Sue Flinders-Adams)

“When you transplant, try not to disturb the roots, just take the whole pot-shaped lump of soil/roots and pop it into its new home.” How many people have heard this story when purchasing a new tree or shrub from a nursery?

We take a shrub out of its container and see white fragile-looking roots and instinctively we don’t want to damage them or add to transplant shock. We know that healthy growth in a shrub is dependent on a good root system, so why would we mutilate or injure them?

Are Roots Really That Fragile?

Well, it turns out that those roots are not as fragile as we think. While you should take care with when transplanting seedlings, especially annual flowers and vegetables, woody perennials, shrubs, and trees all benefit from a more vigorous approach, according to Linda Chalker-Scott, Ph.D., Extension Horticulturist and Associate Professor at Washington State University and one of the ‘Garden Professors’ that I admire for their scientifically-based knowledge of horticulture.

Garden Professors on Facebook or Garden Professors Website

When we purchase gallon-sized pots in the nursery, the plants are often pot-bound, the often suffered from circled root systems, which if not corrected become even more problematic once the shrub is in the ground. Eventually they become girdling roots, which will lead to the early death of otherwise healthy trees and shrubs, as you see below.

(photo courtesy of Tim Hamilton)

Think of it this way – roots respond to respond to pruning in much the same way as the crown—it stimulates new growth. If you prune the roots when you transplant, especially those that are excessively long or misshapen, the plant will respond by generating new, flexible roots that help them establish in the landscape. The best way to do this is by root-washing the shrub – taking it out of the pot, putting it in a wheelbarrow or other container, and washing off all the media so that you can see what the root system looks like.

Two Critical Things to Do

1. Prune the roots in a root-bound shrub or tree to avoid future problems
2. Remove the media (soil) that shrub or tree came in

The second suggestion relates to the soil that comes with your tree or shrub. I always thought you just put it right in the ground, but evidence suggests that (generally) the container media is a soil-less mix with a large proportion of organic matter and pumice. It is best to remove this media as part of your root inspection, and use it as topdressing after planting, followed by mulch.

If you put the media in with your new plant, the material will inhibit root development outside the planting hole. It will also lose water more rapidly than the surrounding native soil (because of its porous nature), resulting in increased water stress to your new transplant.

Watering is Essential

As with all transplanting, regular and deep watering is needed to keep the new shrubs or trees happy while they establish their new root systems. The fall is a great time to plant trees and shrubs so happy planting!

Want To See How It’s Done?

Doug Gifford of Michigan recently posted to the Garden Professors Facebook page about his root washing, root-pruning, and planting of shrubs. You can check out the link here. Credit to Doug for most of the photos on this blog post.

A Special Note

If you plant a shrub or tree already in full leaf they will be more stressed than those that are dormant. Dormant planting is better as all resources go towards root establishment. You may see leaf damage or even death in the short run. But as long as the roots are kept cool and moist throughout the transplanting process, and as long as you keep the area mulched and watered, it should be fine in the long run.

Check out more detail on this issue in this blog post. It talks about the four things that result in landscape planting failures and how changes in the nursery industry have resulted in more problems with roots. Many of these issues also apply to balled and burlapped (B&B) trees – more information here.

This year, Dr. Chalker-Scott extended her experiment to perennials, as talked about in this blog entry  Three months later she revisited the site – here are the results.

For more information on other horticultural myths check out these pages. Even better? Spread the word to others 😊
Horticultural Myths – Dr. Linda Chalker-Scott
Garden Myths (Robert Pavlis’ site – he is based in Guelph, Ontario)