In the Garden:
New England
May, 2008
Regional Report

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Tightly encircling roots of perennials, shrubs, and trees can hamper future growth.

The Root of the Matter

Here's a little quiz to test your root IQ:

1. When you're planting a six-pack of annuals, what's the best way to deal with root-bound seedlings? Is it (a) tease the roots apart before planting, or (b) leave the rootball intact?

2. Is the technique the same if you're planting a tree or shrub?

Plant roots are a bit mysterious because we seldom see how they grow. The only time we see the roots is during transplanting, and after the plant is in the ground we're more concerned with the top growth than what's going on underground. But the roots set the stage for the performance of the plant so let's dig a little deeper and see how we can help enhance the show.

Transplanting Do's and Don'ts
If you could see your annual snapdragon seedling beneath the ground after planting, you'd see new growing points rapidly forming all along the roots at the edge of the rootball (providing the soil is moist and inviting). It turns out that teasing the roots apart only slows the plant down.

Shrubs and trees are a different story. The process of digging and handling container plants can distort the roots, and the distortion is magnified as the roots become thicker and woodier. Encircling roots can choke each other and actually girdle a plant and cause its death.

Ideally, you would be able to inspect the roots of a tree or shrub before buying it by removing it from the container. But if the nursery isn't agreeable to this, you'll have to take your chances and remedy any problems when you get home. If possible, untangle encircling roots, and if this isn't possible, slice through them from top to bottom in several places around the rootball so you can spread them apart.

The soil in the container can also pose problems because it's likely to be lighter and more porous than the native soil in your yard, and roots are likely to keep growing inside this material instead of spreading out. Remove as much of this soil as possible when you plant. Make a small mound in the bottom of the planting hole and spread the roots on top. Use only native soil, without compost and other amendments.

Linda Chalker-Scott, Extension horticulturist and associate professor at Puyallup Research and Extension Center, Washington State University, even advises removing the soil from a balled-and-burlapped tree or shrub at planting time. You can then inspect and correct any root problems. Plus, the heavy clay that's typically a majority of the rootball can cause problems with water flow and root spread. Better to get the plant settled into the native soil right away. This is not an easy step, however, especially with a large tree. And sometimes plant guarantees won't apply if you disturb the rootball of a balled-and-burlapped plant.

Staking Newly Planted Trees
Staking a tree can impact its root development. Most container and balled-and-burlapped trees don't need staking. Bare-root trees usually do. But trees that are staked too tightly aren't able to sway in the breeze, which is necessary for the development of proper girth and roots. They are highly susceptible to blowing over or breaking when the stakes are removed.

If a tree is too weak to stand by itself, give it the support of staking, but stake it as low on the trunk as possible so it can still sway. Use flexible ties with cushioning next to the bark (an old piece of hose works well), and keep them in place for no longer than a year.

Training Roots to go Deep
Roots don't grow TO moisture, they grow IN moisture. To encourage them to grow deeply, you need to water deeply. If you go out with a hose every few days and sprinkle your plants, you will only moisten the soil near the surface and the roots will stay in that zone. Granted, much of the root system does remain in the upper few feet or so of soil, but many roots grow deeper and they help anchor the plant and take in water that lingers even when the surface dries out.

Coexisting With Lawns
Trees in lawns have an especially big obstacle to overcome because lawn watering tends to be shallow and frequent. Some trees respond to this by growing roots so superficially that they can be scalped during mowing, or they may send up rampant suckers. For this reason, willows, Lombardy poplars, red and sugar maples, and serviceberries, among others, are best planted bordering the lawn instead of in the middle of it.

Too much nitrogen is also a problem for trees in lawns because their expansive root systems take up fertilizer meant for the grass. Trees seldom need fertilizer of any kind, and lawn fertilizer, with its high nitrogen, can cause tall, spindly growth that's more susceptible to damage from wind and storms. For a lawn tree, choose one that has relatively deep roots so the excess water and fertilizer will cause less of a problem.

Incidentally, trees and shrubs in the bargain sale area are likely to be bargain priced because they've been sitting around for way too long with root growth hampered. Take a look at the roots before you take one home.


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