Find the root flare: how deep to plant a tree, and how to uncover one planted too deep

The root flare is where a trunk widens into its first main roots, and it belongs at the finished grade or an inch or two above it. A tree buried past its flare seldom dies quickly. It fades over years, while the bark at the soil line stays wet and new roots wrap the trunk. Most trees sold in pots or burlap already sit too deep in their own soil, so find the flare before you dig the hole.

What the root flare is, and why it stays in the air

The flare is plainest on trees that nobody planted. In woods and fields the trunk spreads at the soil line and its main roots run out from it. That is the depth to copy. The roots belong in the soil, and the collar where they meet the trunk belongs in the open air.

Bury the flare and the trunk goes into the ground straight, like a post. The bark at the soil line stays wet and begins to decay. The buried roots get less oxygen and less water. Roots that grow up into the new soil can wrap the trunk out of sight and become girdling roots.

A small error is enough. In a three-year trial of five kinds of container trees and shrubs, a root collar set 3 inches below grade cut the growth or survival of every one. Nearly all of them survived when set at grade or 3 inches above it. Heavy clay makes deep planting worse, because water pools in the hole like a bathtub.

Finding the flare before you plant

Where the flare hides depends on how the tree was grown.

In a pot

A young tree is moved into larger pots as it grows, and a tree set deeper at each move ends with its flare buried. Scrape or wash the potting mix off the top of the ball until the first main root shows. In a University of Florida study of maples, elms and magnolias moved through three pot sizes, most root defects lay hidden under the mix. A visible flare was no sign of sound roots below it.

Cut any root that runs across the top of the ball or curls back toward the trunk. Then shave a thin layer off the outside of the ball to remove the roots that circle the pot wall.

In a burlapped ball

A tree dug from a nursery field can arrive with its flare under several inches of soil, often from machine work in the nursery rows. Open the burlap at the top and remove the soil until the flare shows. In one survey of nursery-grown trees, more than three in four had their root collars buried, by 3 to 12 inches.

On a bare-root sapling

A bare-root sapling has no soil over its roots, but on a young stem the flare may barely show. The topmost root then marks the depth, set just under the surface, as bare-root trees on arrival sets out.

Roots that grow above the flare

Dig into a buried ball and you may meet roots growing straight out of the trunk above the real flare. They sprout from the stem where soil or mulch has been piled against it, and they grow upward toward the surface. The real flare lies below them. Left in place, they can circle the trunk as they thicken and girdle it, so cut them while they are small.

Planting to the flare

The flare sets every measure of the hole:

1. Measure from the flare. Clear the extra soil, and the height of the ball from the flare down is the depth of the hole.
2. Dig wide and no deeper. Make it two to three times as wide as the ball, with an undug floor, since loose soil under the ball lets the tree sink.
3. Check the height. Lay a shovel handle across the hole and set the flare at the finished grade or a little above it.
4. Backfill with the soil you dug. Add nothing, and firm it gently around the ball.
5. Keep mulch off the flare. Spread it in a wide, even layer, never mounded against the trunk, as mulch around a tree sets out.

Set the flare high rather than low, because a tree can settle but never rises. The rest of the planting order is in ten planting mistakes that quietly kill trees.

A few plants we grow go in a little high, or with the ball whole:

• Southern magnolia: the flare about 2 inches above the soil, with any circling roots cut, since magnolias are prone to girdling roots. Zones 6 to 10, 60 to 80 feet.
• Flowering dogwood: a little high where drainage is doubtful. Zones 5 to 9, 15 to 30 feet.
• Flame azalea: the top of the ball a touch above grade, on a raised mound in heavy clay. Zones 5 to 7, 4 to 12 feet.
• Rosebay rhododendron: the root mass a touch above grade, in a hole slightly shallower than the ball. Zones 3 to 7, 10 to 15 feet.
• Pawpaw: from the pot with the ball whole, since its fleshy roots break easily. Zones 5 to 9, 15 to 30 feet.

Signs of a tree planted too deep

A tree planted too deep can look healthy for years. When girdling roots start from roots that circled a nursery pot, the tree seldom survives more than a decade in a yard. On a balled tree, the decline from girdling roots may take 20 to 30 years to develop. Depth is the first thing to rule out when a tree slows year after year:

“The most common reason for the slow decline of trees in the landscape is due to the depth of planting and girdling roots.” (Purdue Landscape Report, Another Case of Mortality from Planting Trees Too Deep)

Look at the base of the trunk first, then the crown:

• No flare. The trunk enters the soil straight, with no widening at its base.
• A trunk that rocks. Pushed gently, a buried trunk shoves the soil aside and opens a gap at its base.
• One flat side. A trunk that runs straight or flat into the ground on one side often hides a girdling root there.
• Dieback on one side. Limbs die on the flat side, or the top of the crown thins first.
• Early fall color. Leaves turn pale or scorched, color early and drop early.
• Cracks and decay. The bark cracks and decays at the soil line.
• A lean. A tree with severe girdling roots may lean, or break at the base in a storm.

Depth alone can start girdling roots. In a Clemson University trial published in 2006, red maples set 6 inches deep had roots encircling 48 percent of the trunk three years later, against 14 percent for maples set at grade. Half the Yoshino cherries planted 6 or 12 inches deep died within two years, while every cherry at grade lived.

Uncovering a buried flare

A tree planted this season that shows no flare can be lifted and reset at the right depth. An older tree is dug out where it stands, in a job called a root collar excavation.

Digging down to the flare

Pull back the mulch, then remove the soil around the trunk until it widens into roots. On established trees the flare has been found 6 to 12 inches down. A small job goes by hand with a plastic trowel or weeder, since a metal blade can cut the bark. Arborists clear bigger trees with an air spade, which blows the soil away with compressed air.

Take the soil back to the original grade wherever you can. Where that leaves the trunk in a hollow, dig a trench so water drains away from the bark.

What to cut and what to leave

Small girdling roots come out with a chisel and mallet. Take out several inches of each where it touches the trunk, so the two cut ends cannot grow back together. Where several roots girdle one tree, remove the worst first and wait a season or two before taking the next. Leave every main root that runs away from the trunk. A tree usually has four to seven, and cutting one near the trunk can take up to a quarter of the root system.

A large root that has fused to the trunk is better left in place, or weakened with a V-shaped notch cut into its top half. Taking out a big girdling root is a gamble:

“For large girdling roots on established trees, correcting the problem can be difficult. Removal of the girdling roots may cause enough damage to the root system to hasten the decline.” (The Morton Arboretum, Tree Root Problems)

A girdling root over 2 inches thick is a job for an arborist. Afterward keep the flare open to the air, with mulch no deeper than 2 to 3 inches.

Before the next hole is dug

The flare is easiest to fix before a tree goes into the ground:

• A sapling about to be planted. Find the flare or the topmost root first, then follow bare-root trees on arrival through the first week.
• A sapling still to buy. Blue Whale Trees sells most plants as seedlings and young saplings grown from seed, usually 12 to 18 inches tall when they ship. Each plant’s page says whether it travels bare-root or potted.
• A flare you cannot read. Describe the tree through the support page, and a photo of the whole tree and a close-up of its base can follow by email once we reply.

Common questions

What is a root flare on a tree?

It is the widening at the base of the trunk where the first main roots spread out from it. It should sit at the soil line or just above it, open to the air.

How do I find the root flare on a tree in a pot?

Scrape or wash the potting mix off the top of the ball until the first main root shows, often several inches down. Measure the depth of the hole from that root to the bottom of the ball.

What do I do if I planted a tree too deep?

Lift a tree planted this season and reset it with the flare at grade. For an older tree, take the soil away from the trunk down to the flare, by hand or with an arborist’s air spade.

What is the difference between circling roots and girdling roots?

Circling roots run around the inside of a pot, where they hit its wall and turn. Once one presses against the trunk and both thicken, it is a girdling root, and it slowly strangles the trunk.

Sources

• How to Plant Trees and Shrubs: The Morton Arboretum: a hole two to three times as wide as the ball and only as deep, an undisturbed floor so the tree cannot sink, the flare at least half an inch above the soil with the topmost roots just below it, a shovel laid across the hole, field-grown balls already too deep and the burlap opened to find the flare, shaving circling roots off a container ball, unamended backfill, and mulch in an even layer never mounded against the trunk.
• Tree Root Problems: The Morton Arboretum: girdling roots from a pot killing a tree within about a decade and those of a balled tree taking 20 to 30 years, four to seven main roots with up to a quarter of the root system in one, and the quotation on removing large girdling roots.
• Girdling Roots: University of Maryland Extension (updated 2024): a straight side with no flare over a buried girdling root, the upper crown thinning first, pale or scorched leaves with early color and early drop, leaning and broken trees, girdling roots caught while small and cut out with a chisel and mallet by several inches at the trunk, a large root grafted to the trunk left or notched, and roots over 2 inches left to an arborist.
• Another Case of Mortality from Planting Trees Too Deep: Purdue Landscape Report (Kyle Daniel, 2023): bark decay from soil moisture around a deep trunk, the bathtub that heavy clay makes, the flare plain on trees in natural areas, the topmost root at grade where no flare shows, and the quotation on slow decline.
• Stem Girdling Roots: Purdue Landscape Report (John Bonkowski, 2022): the base of the trunk as the first place to look, a one-sided flare or none over a girdling root, trees that lean or blow over, roots put out into mulch piled on the trunk, pot-bound stock and roots turning at the pot wall, an encircling root cut at planting, compression as root and trunk thicken, and the worst root removed first with the rest left a season or two.
• Plant Health Alert - Excavate Root Collars to Save Trees: N.C. Cooperative Extension, Henderson County (Steve Pettis, 2024, updated 2026): a trunk flat on its dying side, root collars buried 6 to 12 inches, excavation done by a tree care firm, soil taken back to the original grade, a trench to drain the excavated collar, the collar open to the air, and mulch no deeper than 2 to 3 inches.
• The Perils of Planting Trees Too Deeply: Ohio Department of Natural Resources, Division of Forestry (Stephanie Miller and Drew Todd, 2003): the root collar and its flare, a trunk going into the ground like a pole, the rocking test, less oxygen and water for buried roots, new roots from a buried trunk growing toward the surface and wrapping it, stress that takes several years to show, decay and cracks, sinking backfill and resetting the tree, several inches of extra soil on balled trees, finding the flare before planting, plastic hand tools for small excavations, and the air spade.
• Effects of Planting Depth on Landscape Tree Survival and Girdling Root Formation: C. Wells, K. Townsend, J. Caldwell, D. Ham, E.T. Smiley and M. Sherwood, Arboriculture & Urban Forestry 32 (2006): the Clemson University trial of red maples and Yoshino cherries planted at grade, 6 and 12 inches deep, its survival and girdling root results, the air spade used to expose the collars, and a survey that found buried root collars on more than three in four nursery-grown trees, 3 to 12 inches down.
• Planting Depth Affects Root Form of Three Shade Tree Cultivars in Containers: E.F. Gilman, C. Harchick and M. Paz, University of Florida, Arboriculture & Urban Forestry 36 (2010): deeper flares and more girdling roots from deep planting at each shift to a larger pot, defects hidden under the potting mix, a visible flare unrelated to sound roots, and washing the mix off the top to inspect the roots.
• Below-Grade Planting Adversely Affects Survival and Growth of Tree Species from Five Different Families: M.A. Arnold, G.V. McDonald, D.L. Bryan, G.C. Denny, W.T. Watson and L. Lombardini, Arboriculture & Urban Forestry 33 (2007): five container-grown trees and shrubs set 3 inches below grade, at grade and 3 inches above, their root flares otherwise called root collars, growth or survival cut in every species at 3 inches below, and nearly all surviving at or above grade.