Name: Koala Tree
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Look at where your tree meets the ground. A healthy tree widens at the base into its main roots. If the trunk goes straight into the ground like a pole, the root flare is probably buried.

What the root flare is

The root flare is where the trunk widens and divides into the main roots. It’s meant to be at or just above the soil. The bark there is trunk bark, not root bark, and it isn’t designed to stay wet.

Why a buried flare matters

Moist bark can decay. Soil or mulch held against the trunk keeps the bark wet, which invites rot and insects.
Girdling roots. Roots can grow up into deep mulch or soil and circle the trunk, slowly squeezing it as both grow.
Planting too deep. Many buried flares start at planting, when the tree goes in lower than it grew in the nursery.

The mulch volcano

A cone of mulch piled up against the trunk is a common sight. It looks tidy, but it causes the problems above and can shed water away from the roots instead of letting it soak in.

If the trunk goes into the ground like a pole, the root flare is probably buried.

What a good mulch ring looks like

Wide and flat, as wide as is practical. Out towards the edge of the canopy is ideal.
About 5 to 10 cm deep (2 to 4 inches) of wood chips or shredded bark.
Pulled back from the trunk so the root flare is visible and the bark stays dry.
Topped up as it breaks down, rather than piled higher each year.

A mulch ring also keeps mowers and string trimmers away from the trunk, where repeated nicks in the bark do real damage.

Fixing a buried flare

If it’s just mulch, pull it back from the trunk by hand. Go gently near the bark. If soil has built up over the flare, or you suspect girdling roots, an arborist can excavate the base with an air tool that blows soil away without cutting roots. Then the roots and flare can be checked, and any problem roots dealt with.

Key takeaways

The base of the tree, in five lines

The root flare should be visible at or just above the soil.
Mulch against the trunk keeps bark wet and invites decay.
Make the ring wide and flat, about 5 to 10 cm deep.
Keep mulch pulled back from the trunk.
A buried flare can be excavated and checked by an arborist.

This is general information. Every tree and site is different. For advice on a specific tree, get a free quote or book a Certified Arborist Assessment.

About the author

Jason Korkidakis

Jason is Koala Tree’s Owner and Lead Arborist in London, ON. He leads an 8-person crew and assesses trees for homeowners, condo boards and property managers.

ISA Certified Arborist ON-3263ATRAQ qualifiedPPQ qualified

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