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It’s Shrub and Tree Planting Time… Mind Your Roots!

It is hard to believe it is already mid-September. While many folks get excited about spring in the garden, experienced South Carolina gardeners know that autumn is the sublimest of seasons. Crystal clear blue skies, cool, crisp breezes, and the first tinges of fall color signal the end of our hot, humid summer.

Fall is the best time to plant woody ornamental shrubs and trees. The soil does not freeze in the winter. Therefore, tree and shrub roots grow into the surrounding soil to access vital nutrients and water while leaf and flower growth halts during the plant’s winter dormancy.

Many believe roots grow like a plant’s top, reaching as deep into the soil as the branches reach the sky. However, tree and shrub roots grow radially from the plant’s trunk and go past a plant’s farthest branches. Consider that the roots of many massive trees may reach down only 18 to 24 inches into the ground.

Plant roots grow out radially from the trunk instead of growing down deep into the soil. N. Jordan Franklin, ©2021 HGIC, Clemson Extension

Plant roots grow out radially from the trunk instead of growing down deep into the soil.
N. Jordan Franklin, ©2021 HGIC, Clemson Extension

Ever notice how a tree trunk gradually widens as the trunk goes into the ground? This area is known as the root flare, and it is where the trunk transitions into the plant’s topmost roots. When planting trees or shrubs correctly, the root flare is visible above the ground. The top roots are at, or just slightly below, the soil surface after planting. Burying the root flare too deeply will eventually kill the plant because the roots are too deep to exchange air with the atmosphere. Additionally, the root-air exchange with the atmosphere is the reason not to pile mulch too deeply on plant trunks and roots.

(Left) The root flare is clearly visible on this established Japanese maple. (Right) The root flare of a recently planted ironwood tree is above the soil surface. N. Jordan Franklin, ©2021 HGIC, Clemson Extension

(Left) The root flare is clearly visible on this established Japanese maple. (Right) The root flare of a recently planted ironwood tree is above the soil surface.
N. Jordan Franklin, ©2021 HGIC, Clemson Extension

Trees and shrubs often come from the nursery planted too deeply in their container or balled-in-burlap root balls. Container-grown plants may suffer circling roots in the pot. When these problems occur, take steps to correct the issues before putting a shovel into the ground. Otherwise, the planting hole may be too deep for the actual root ball. Determine the correct height of the root ball after the topmost roots are exposed, and the circling roots are corrected. This practice also reveals the actual width of the root ball as the roots are spread out radially from the plant trunk.

When planting trees and shrubs this way, the planting hole is shallower than if the plant were removed from the container and placed in the ground without correction. Dig the planting hole two to five times wider than, and only as deep as, the root ball from the topmost roots to the bottom roots. The root ball should sit on undisturbed soil at the bottom of the planting hole. Then, backfill the roots with the native soil. That’s right: DO NOT AMEND THE BACKFILL! Amended backfill causes soil structure problems that can lead to plant failure.

For more information on plant trees and shrubs, visit HGIC 1001, Planting Trees Correctly, and HGIC 1052, Planting Shrubs Correctly.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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