What Tree Mulching Really Does for Your Garden Soil

The simple version—Tree mulching helps regulate soil moisture, protect roots, and improve soil health when it’s done properly and in the right places.

Mulch is one of those things homeowners feel they should understand.

It gets recommended after tree work. It turns up in garden beds. Councils talk about it. Landscapers love it. And yet, there’s often a vague sense that it’s either cosmetic… or some kind of gardening cure-all.

The truth sits somewhere in the middle.

On Sydney’s Northern Beaches and North Shore, tree mulching can make a noticeable difference to how trees cope with heat, rain, and compacted soil. But only if it’s used with a bit of care and a bit of restraint.

What mulch actually does (and what it doesn’t)

At its most basic, mulch is a protective layer.

It sits on top of the soil and acts as a buffer — slowing evaporation, moderating temperature swings, and reducing weed growth. For trees, that protection matters most around the root zone, where moisture levels and soil structure quietly determine long-term health.

What mulch doesn’t do is magically fix poor drainage, revive a declining tree overnight, or compensate for compacted soil beneath it. It helps. It supports. It doesn’t perform miracles.

That misunderstanding is common.

Why mulch matters more around trees than lawns

Lawns get watered often. Trees usually don’t.

Once established, most trees rely on rainfall and the soil’s ability to hold moisture. In suburbs with sandy profiles — common across parts of the Northern Beaches — water drains quickly, especially during warmer months.

A layer of mulch slows that loss. It gives rain a chance to soak in instead of running off or

evaporating. Over time, as organic mulch breaks down, it also feeds the soil below. Quietly. Gradually.

Not fast enough to notice day-to-day, but enough to matter over years.

How much mulch is enough?

This is where things often go wrong.

It’s not unusual to see mulch piled high against a trunk, forming a neat little cone. It looks tidy. It feels intentional. But it can cause problems.

Mulch should sit around a tree, not against it.

A general rule is a broad, shallow layer — a few centimetres deep — spread over the root zone, keeping the base of the trunk clear. Roots like oxygen as much as they like moisture. Smothering them defeats the purpose.

More isn’t better. Wider is usually smarter.

Mulch types homeowners tend to ask about

Not all mulch behaves the same way.

• Wood chip mulch is common after tree work and suits established trees well. It breaks down slowly and handles rain without washing away.

• Fine bark mulch looks neat but can compact over time if layered too thickly.

• Dyed mulches are mostly aesthetic. They don’t add anything extra for trees.

• Green waste mulch can be useful, but quality varies.

  
  

In Sydney’s coastal areas, heavier mulches tend to stay put better during storms. Lighter products can drift or wash into drains after heavy rain.

Tree mulching after pruning or removal

After tree work, mulch often serves a practical purpose.

It helps protect disturbed soil, reduces compaction from foot traffic, and supports nearby plantings adjusting to more light or exposure. In some cases, mulch from the tree itself is reused on-site, closing the loop in a fairly sensible way.

That’s usually where tree mulching feels most logical to homeowners — it’s visible, immediate, and tied to something tangible that’s just happened.

What an arborist looks for before recommending mulch

Mulch isn’t automatic.

Before suggesting it, an arborist will usually think about:

• Soil type and drainage

• Tree species and root sensitivity

• Slope and water flow

• Existing compaction

• Proximity to fences, paths, and structures

• How the area is actually used

  
  

On the North Shore especially, many gardens sit on heavier soils that hold water longer. In those cases, too much mulch can keep things overly damp.

It’s a balancing act, not a formula.

Seasonal timing makes a difference

Mulching before summer helps soil retain moisture through heat. Mulching after heavy pruning can reduce stress. Mulching during prolonged wet periods, though, sometimes needs restraint.

Homeowners often assume there’s a “best month” for it. In reality, it’s more about conditions than the calendar.

Weather patterns matter more than seasons.

Common questions that come up

Will mulch attract termites?

Mulch itself doesn’t cause termites but placing it against structures or trunks can create favourable conditions. Placement matters.

Do I need to remove old mulch first?

Usually, no — unless it’s compacted or excessive. Old mulch breaking down is often beneficial.

How often should mulch be topped up?

When it’s visibly thinning or breaking down. That might be yearly, or it might be longer.

Can I mulch around newly planted trees?

Yes, gently. Keep it light and clear of the trunk.

Is tree mulching worth doing at all?

When done properly, yes. It supports soil health over time, which trees rely on more than most people realise.

A quiet support act for trees

Tree mulching isn’t dramatic.

It doesn’t shout. It doesn’t transform a garden overnight. And it rarely gets credit when trees are doing well.

But across Sydney’s Northern Beaches and North Shore, where soils, weather, and established trees all interact in complex ways, it plays a steady supporting role. One that’s easy to overlook — and easy to misuse — but genuinely helpful when applied with a bit of understanding.

Sometimes the most effective things are the least exciting ones.