Tree Planting Depth

Planting trees too deeply has become the Number One reason why trees fail.

Mature tree with visible flare (PxHere) Public Domain

Is your tree failing to thrive? Does it seem overly susceptible to fungal diseases and pests? Are leaves smaller, scorched, or otherwise discolored? Has seasonal leaf color change started occurring earlier? Are wilting, early leaf drop, or twig dieback been occurring? Are you seeing more water sprouts and suckers? Have you noticed less new twig development? It may be that your tree is planted at the incorrect depth. Even heavy fruit production can indicate a problem. Confused? Don’t be. Producing fruit is a tree’s way of continuing the species. If the tree is dying, it will put everything it has into ensuring a big crop of potential future generations.

A properly planted tree shows a flare at the base of the trunk. If your tree looks more like a fence post, it is probably planted too deeply. In the world of botany, a tree planted too deeply is said to be planted ‘below grade’. Trees with exposed roots were planted too shallowly and are ‘above grade’.

Proper planting depth (USDA Forest Service) Public Domain

Knowing how to plant a tree at the proper depth (or how to correct the problem once it occurs) is the best way to keep your trees healthy and productive. 

Start your trees better

When you first buy a young tree, it is usually in a container or the roots are balled up in a burlap bag. In both cases, the young tree has 5 to 20% less feeder roots than a similarly sized tree growing in the ground would have. As a result, these young trees dry out more easily and are easily stressed. If that weren’t problem enough, putting that stressed tree in the ground at the wrong depth can kill it, though it may take a few years. The goal of planting is to get your tree in the ground in such a way that new roots can grow quickly and properly.

Proper planting depth

The majority of a tree’s roots are in the top 18 to 24 inches of soil. They spread out horizontally and vertically from the center, well beyond the drip line, in their search for food, water, and air. [The drip line is the outer circumference of the tree canopy, where rain water drips to the ground.] To plant a tree at the proper depth, use these tips:

1. First, do not assume that your tree was planted at the proper depth at the nursery.
2. After hydrating your new tree, take it out of the container and thoroughly inspect the roots. Remove any that look diseased or damaged. Spread them out and look at the overall shape. If they are growing in a spiral, see if you can unwind them. If you can’t unwind them, cut them back to the point where they can be straightened out somewhat.
3. Identify the root crown (also known as root collar), where the trunk flares outward and joins the root system. This is not the same thing as the swelling seen where trees have been grafted onto root stock. The different bark textures and colors can help you identify the root collar.
4. Dig a planting hole that is 2 or 3 times wider than the spread out roots, and slightly more shallow than the roots or the root ball [This compensates for the soil texture interface, or the difference in macropores and micropores between the local soil and the filler, or backfill, soil. Trees with a 1-inch diameter trunk should be planted 1 inch above the soil line; trees with a 2- to 4-inch diameter should be planted 2 inches above the surrounding soil line. As the backfill soil settles, so will the tree.]
5. Do not place backfill soil on top of the root ball or up against the root collar.
6. Planting on a slope requires a certain amount of terracing.

Ultimately, you want at least two structural roots to be in the top 1 to 3 inches of soil. 

Planting too deeply

The roots closest to the surface are responsible for a large portion of a tree’s respiration. Tree respiration is not the same thing as human breathing. Tree respiration refers to the process by which a tree performs the gas exchange used to generate or release energy. If a tree is planted too far below grade, those surface roots will still grow horizontally and be unable to get at the air they need. 

Planting too shallowly

The primary vertical roots of trees planted too shallowly (above grade) will not grow out into the air. They simply dry up and die. This reduces the water and nutrients available to the growing tree. These upper roots may also try growing into the mulch, where there is limited food and water, or they will simply go around in circles, becoming root bound in the planting hole. This is one way that girdling roots occur.​​

Girdling roots can kill a tree (cultivar413) CC BY 2.0

Girdling roots

Girdling roots are those lateral roots found just below the surface that have, for one reason or another, started growing in circles around the tree. This is common with trees kept in containers for too long. Another common way girdling roots occur is when the roots are ‘spun’ into the planting hole, rather than spread out horizontally. Make sure that your planting hole is wide enough to allow those important roots to spread out the way they were meant to grow. ​
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Girdling roots can also occur in compacted soil. If the surrounding soil is compacted, young roots simply cannot penetrate, so they go around and around, looking for a path in their search for moisture, minerals, and air. Curbs, large stones, and building foundations can have similar effects. Girdling roots will kill your tree in 5 to 15 years. It won’t matter how well you fertilize or irrigate your tree.

Speaking of irrigation, be sure to avoid standing water around the trunk of your tree. This can lead to crown rot and other fungal diseases. Instead, use soaker hoses or build an irrigation ring at the tree’s drip line.

Are your trees planted properly?

The easiest way to tell if a tree is planted properly is to dig down an inch or two, with your fingers, next to the trunk. You should come across 4 to 11 substantial roots. If all you find are delicate feeder roots, your tree is planted too deeply. If the roots are visible from the surface, it is too shallow.

How to correct planting depth errors

Trees planted too deeply (below grade) should be dug up, the roots inspected, and then replanted at the proper depth. Trees planted above grade need more soil added around the trunk. First rake the area under the tree to loosen the existing soil. Then add a layer of soil to the proper depth, gently sloping away from the trunk. 

Proper planting depth is critical to your tree’s health. Trees planted above or below grade will never thrive. Believe me, it is much easier to do it right in the first place.