Southwest Gardener

Digging the Right Depth for a Long-Living Tree

A tree’s hole should be no deeper than the depth of the tree’s root ball.
Marisa Thompson, February 2018

Q: Why is it recommended to plant a tree in a hole twice as wide as the root ball and the exact same depth?

A: Planting a tree is a lifetime investment and very much worth the extra effort associated with it. The old “pop and drop” method of popping the plant out of the container and dropping the root ball directly into the ground is just not good enough.

Roots have a tendency to spiral when grown in nursery pots. They must be cut to avoid slow suffocation and possibly death. Before planting, be sure to loosen the root ball and cut any spiraling roots so that new root growth is trained to grow outward and you are maximizing root-soil contact.

A hole with equal depth and twice as wide as the root ball encourages lateral root growth. If you have relatively loose soil, twice the diameter of the root ball may be sufficient. Instead of backfilling with the soil you removed, you can loosen the existing perimeter of the hole, collapsing in the sides of the hole.

A major reason to use a hole that is the same depth of the containerized tree is the crucial area where the trunk meets the soil (sometimes called the root collar). If you were to push away the soil at that spot, you might see a slight color distinction that marks the soil line. When planting a tree, make note of where that line is on the tree trunk and be sure that the final placement keeps that line at exactly the same spot.

If you dig the hole too deep, that trunk flare will be covered up after planting. This kills trees all the time and is why the hole should be no deeper than the depth of the tree’s root ball. A typical tree develops as much as 95% of its total root mass in the top 3 feet of soil and 75% in the top foot alone. This means the roots extend horizontally two or more times the total height of the above-ground portion of the tree.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center. She can be reached at


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