Mulching around trees is one of the simplest ways to improve growing conditions, but it is also surprisingly easy to get wrong.
The most common mistake is piling mulch up against the trunk of the tree. You may have seen this done in gardens, parks and landscaping projects, where mulch forms a mound or volcano around the base of the tree.
It might look tidy, but that isn't how tree mulch should be applied.
The correct approach is a wide, relatively flat ring of mulch with the tree trunk and root flare left completely clear.
This guide focuses specifically on how to mulch established and newly planted trees correctly.
What Should Mulch Around a Tree Look Like?
Think wide and flat rather than high and narrow.
For most trees, a good starting point is:
- Approximately 75–100mm of mulch
- Mulch kept clear of the trunk
- The root flare remaining visible
- A wide mulch ring extending away from the tree
- An even layer rather than a mound
- No soil or mulch piled over the base of the trunk
If you already have mulch around the tree, check its existing depth before adding more. You don't need to add another 75–100mm every time you top it up.
What Is the Root Flare?
The root flare is the area at the bottom of a tree where the trunk begins to widen before the main roots enter the soil.
On a correctly planted tree, you should normally be able to see this transition rather than having the trunk disappear straight into a pile of soil or mulch.
When applying mulch, leave the root flare exposed.
Don't build mulch upwards around the trunk in an attempt to create a neat mound.
Why Shouldn't Mulch Touch the Tree Trunk?
Tree trunks are designed to be above ground and exposed to the air.
When mulch is continually piled against the trunk, it can keep the bark unnecessarily damp and bury the natural root flare.
This is commonly known as volcano mulching.
Instead, pull the mulch back from the trunk to create a clear ring around its base.
The end result should look more like a flat doughnut than a volcano.
How to Mulch Around a Tree Step by Step
1. Check the Base of the Tree
Before adding any mulch, find the base of the trunk and identify the root flare.
If old mulch has already been piled against the trunk, pull it back until the base of the tree is exposed.
Don't simply spread another layer over what is already there.
2. Remove Problem Weeds and Grass
Remove established weeds and unwanted grass from the area you intend to mulch.
Be careful around mature trees with roots close to the surface. Avoid aggressive digging, rotary hoes, spraying or anything else likely to damage roots.
A mulch ring also has the added advantage of reducing the need to mow or use a line trimmer immediately beside the trunk.
3. Spread the Mulch in a Wide Ring
Spread your mulch evenly around the tree rather than concentrating it immediately beside the trunk.
Where space allows, extend the mulched area well beyond the base of the tree.
For younger trees, spreading mulch towards the edge of the canopy creates a much larger protected root-zone area than a small circle immediately around the trunk.
You don't necessarily need to reach the entire canopy of a large mature tree. Just make the mulched area as wide as is practical for your garden.
4. Aim for Around 75–100mm Deep
For arborist mulch, approximately 75–100mm is generally a useful depth.
The important point is to measure the total mulch depth, not simply the amount of new material you're adding.
If an established tree already has 50mm of mulch remaining, you may only need a top-up rather than another completely new layer.
For more general garden-bed preparation and application, see our guide to how to apply mulch for the best results.
5. Pull Mulch Away From the Trunk
Once everything is spread, go back around the tree and pull the mulch away from the trunk.
You should be able to clearly see the base of the tree and its root flare.
There should be no mulch leaning or piled against the bark.
6. Leave the Mulch Flat
There's no benefit in shaping mulch into a mound.
Keep the finished surface relatively flat and even.
A wide, flat mulch ring protects substantially more soil around the tree than a tall pile.
What Is a Mulch Volcano?
A mulch volcano is exactly what it sounds like: mulch piled into a cone around the trunk of a tree.
It often happens when another layer of mulch is added every year without checking what is already there.
Over time, the mound gets higher and higher.
If you have an existing mulch volcano, don't add another layer on top.
Pull the material away from the trunk and redistribute it further out across the surrounding ground.
The objective is to expose the root flare and turn the mound into a wide, relatively shallow mulch ring.
Can You Put Mulch Over Exposed Tree Roots?
Yes. Organic wood-chip mulch can be particularly useful where large surface roots make grass difficult to maintain.
Rather than cutting exposed roots or repeatedly hitting them with a mower, you can spread mulch over the surrounding area.
Simply follow the natural ground level, cover the surrounding root zone with mulch.
How Should You Mulch a Newly Planted Tree?
The same basic principles apply to a new tree.
Spread the mulch horizontally across the surrounding soil.
One common mistake with new trees is making an extremely small mulch circle around the planting hole.
Where possible, make the ring considerably wider. This reduces competition from surrounding grass and creates a larger mulched area around the developing root system.
Just remember: mulch goes around the tree, not up the tree.
Common Tree Mulching Mistakes
The main mistakes we see are:
- Piling mulch against the trunk
- Covering the root flare
- Applying mulch far too deeply
- Adding a full new layer every year without checking the existing depth
- Making the mulch ring unnecessarily small
- Adding thick layers of soil over surface roots
- Cutting or damaging exposed roots before mulching
- Allowing grass to grow right against the trunk and then damaging the bark with a mower or line trimmer
I know we repeat ourselves a bit - tree mulching is very straightforward if you follow the above rules.
What Type of Mulch Should You Use Around Trees?
Organic wood-chip mulch is well suited to larger tree rings because it creates a natural covering over the soil and gradually breaks down over time.
At Canterbury Mulch Delivery, we supply aged arborist mulch made from locally sourced tree material.
If you're deciding between freshly chipped material and mulch that has already been stored and aged, we've covered that separately in our guide to fresh mulch versus aged mulch.
How Much Mulch Do You Need Around Your Trees?
For one tree, measure the approximate width of the area you want to mulch and choose your intended depth.
For multiple trees, shelter belts or larger planting areas, the required volume can add up surprisingly quickly.
You can use our free mulch calculator to work out how many cubic meters you need before ordering.
The Simple Rule for Mulching Trees
If you remember one thing, make it this:
Wide and flat, with the trunk clear.
Keep the root flare visible, spread the mulch across as much of the surrounding root area as practical and avoid piling material against the tree.
It's a simple job, but getting the shape and depth right makes a big difference.
If you're ready to mulch trees or larger planting areas, you can view our aged arborist mulch load sizes and choose the amount that suits your project.
Tree-care information reviewed by the arborists at Canterbury Tree Experts
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