Can You Cut Roots Without Permanently Killing Your Tree?

The short answer is yes, but only if it's done carefully and for the right reasons. Tree roots can lift driveways, crack paving, invade drainage pipes and push against retaining walls and house foundations. For many Wollongong homeowners, the temptation to grab a saw and remove the problem root is strong. Cutting the wrong root, or too many roots, can seriously destabilise a tree or cause a slow decline that only becomes obvious months or even years later.

This guide explains how roots work, how much you can safely remove, when to leave the job to a qualified arborist, and what to consider under local Illawarra conditions and council rules in 2026.

Why Tree Roots Matter More Than Most People Realise

Roots do far more than hold a tree upright. They absorb water and nutrients, store energy reserves (carbohydrates) and anchor the tree against wind. Most of the roots responsible for water and nutrient uptake are fine, fibrous feeder roots in the top 30 to 60 centimetres of soil. Larger structural roots, which are thick and woody, provide stability and transport resources.

Contrary to popular belief, roots rarely grow straight down like a mirror image of the canopy. Most spread outward, often two to three times the width of the canopy, and stay relatively shallow. That is why a root problem near a driveway or fence line can involve a tree standing several metres away.

Structural Roots vs Feeder Roots

Structural roots are the large, woody roots close to the trunk. Cutting these can compromise the tree's stability and open large wounds that invite decay. Feeder roots are smaller and more numerous, and a tree can usually tolerate losing a portion of them, provided it is healthy and the loss is not excessive.

How Much Root Can You Safely Cut?

There is no single number that suits every tree, but arborists commonly work from a few widely accepted guidelines:

Roots under 2–3 cm in diameter: Generally low risk to cut cleanly, especially on a healthy tree.
Roots 3–5 cm in diameter: Should be assessed individually. Cutting one may be acceptable, but think about its position and function.
Roots over 5 cm in diameter: Treat with caution. These are often structural and should only be cut following professional advice.
Total root loss: Try to keep removal well below 20 percent of the root system. Many arborists prefer to stay closer to 10 percent.
Distance from trunk: The closer to the trunk you cut, the greater the risk. A common rule of thumb is to avoid cutting within a distance of about six times the trunk diameter, measured at chest height.

These are guidelines, not guarantees. Australian Standard AS 4970-2009 https://treeremovalwollongong.com.au/about/ (Protection of trees on development sites) is widely referenced by arborists and councils. It describes a Tree Protection Zone based on trunk diameter and a smaller Structural Root Zone where cutting is most hazardous. Any significant root work near a tree should be informed by these principles.

Factors That Affect How a Tree Responds

Two trees of the same size can react very differently to the same root cut. Several variables influence the outcome.

Species

Some species tolerate root disturbance better than others. Many eucalypts, figs and willows regenerate roots relatively readily, while others, such as certain native rainforest species and some pines, can be more sensitive. Wollongong's mix of native Illawarra species, coastal banksias, Moreton Bay figs, camphor laurels and street plantings means that the right approach varies from property to property.

Age and Health

Young, vigorous trees recover faster than mature or declining ones. A tree already stressed by drought, disease, compacted soil or previous damage has fewer reserves to rebuild what it loses.

Season and Timing

Timing matters. Root pruning when the tree is actively growing but not under heat stress usually gives better recovery. In the Illawarra, late winter to early spring is often a sensible window, as soil moisture tends to be better and the tree is about to push new growth. Avoid cutting roots during a prolonged hot, dry spell, as the tree can struggle to take up enough water to sustain its canopy.

Soil Conditions and Slope

Much of Wollongong sits on sloping ground between the escarpment and the coast, and the area is known for heavy rainfall events and, in some places, clay-rich or shallow soils. Roots on a slope often play an important role in holding the tree in place. Cutting roots on the downhill side or in saturated soil can increase the chance of a tree leaning or failing in strong wind, which is a real consideration given the region's storm patterns.

Signs You've Cut Too Much

Damage from root cutting is often delayed. Watch for these warning signs in the months afterwards:

Thinning canopy or leaf drop outside the normal seasonal pattern
Dieback in upper branches or the crown
Smaller, yellowing or wilting leaves
Excessive epicormic shoots (sprouting along the trunk or main branches as a stress response)
Fungal growth, such as mushrooms or brackets, near the base
The tree leaning or the soil heaving on one side after wind or rain

If you notice any of these, contact a qualified arborist promptly. Early intervention, such as improved watering, mulching and monitoring, can sometimes save a stressed tree.

Safer Ways to Cut Tree Roots

If root removal is unavoidable, the method matters as much as the amount.

Identify the root and its function. Carefully excavate by hand or use air excavation to expose the root without damaging others. Avoid heavy machinery near the trunk.
Assess alternatives first. Consider whether the problem can be solved without cutting, for example by bridging the root with a raised path or adjusting the surface above it.
Make clean cuts. Use sharp tools such as loppers, a pruning saw or a root-pruning saw. Avoid tearing or crushing, which creates ragged wounds that heal poorly.
Cut at the right point. Trim back to a side root or a point where the cut can heal properly rather than leaving a stub.
Backfill promptly. Cover exposed roots with soil quickly so they do not dry out, and keep the area moist.
Aftercare. Apply organic mulch (kept clear of the trunk), water deeply during dry weather and avoid fertilising heavily straight away.

Alternatives to Cutting Roots

In many cases, you can manage root problems without cutting at all. Options include:

Re-routing or redesigning hard surfaces. Replacing a cracked concrete path with permeable pavers, timber decking or a suspended slab on piers allows roots to continue growing underneath without damage.

Installing root barriers. A properly installed root barrier can redirect roots downward and away from structures. Barriers work best when installed before problems arise and must be fitted correctly. A poorly placed barrier can cut roots just as harshly as a saw.

Using flexible materials. Gravel, mulch or flexible paving can reduce damage from small amounts of root growth.

Pipe repairs. If roots are entering drainage lines, relining the pipe or replacing old clay or earthenware sections with modern sealed pipe often solves the problem without harming the tree. Roots generally only enter pipes through existing cracks or joints, so repairing the pipe is usually a more lasting fix than cutting roots repeatedly.

Council Rules and Permits in Wollongong

Before cutting any significant roots, check whether the tree is protected. Wollongong City Council regulates tree work through its development control plan and related policies, and some trees require approval before they are pruned, damaged or removed. Protection can depend on factors such as species, size, location, heritage or environmental zoning, and whether the tree is on private land or a council nature strip.

Key points to keep in mind:

Cutting major roots can count as damaging a tree, even if the trunk and canopy are left untouched. Street trees and trees on council land cannot be pruned or root-cut by residents without authorisation. Properties near the escarpment, in environmentally sensitive zones or in heritage conservation areas may have additional restrictions. Penalties for unauthorised work can be significant, so confirm the requirements with council before starting. Rules can change, so always check the current provisions in 2026 rather than relying on older information.

If a neighbour's tree is the source of the problem, you generally cannot simply cut its roots whenever you like, and the legal position under NSW trees legislation can be complicated. Talking to the neighbour first and obtaining professional advice is the safest route.

When to Call a Qualified Arborist

DIY root cutting is risky for anything beyond small, minor roots. Engage a qualified arborist, ideally holding AQF Level 5 consulting qualifications for assessments, when:

You need to cut roots thicker than a few centimetres. The tree is large, mature, heritage-listed or protected. The roots are close to the trunk or on the slope side of the tree. You are planning building work, a new driveway, a pool or a retaining wall near the tree. Roots are affecting underground services or foundations. You are unsure whether the tree is stable.

An arborist can carry out a tree risk assessment, use tools such as air spades to expose roots without cutting them, advise on root pruning in stages across seasons, and prepare reports that councils often require for approvals. In some cases, they may recommend that removal of the tree is a safer and more cost-effective option than trying to manage persistent root conflicts.

Staged Root Pruning for Larger Projects

When a lot of root removal is unavoidable, such as ahead of a construction project, staged pruning can reduce shock. This involves cutting roots in sections over several months, allowing the tree to produce new feeder roots closer to the trunk before the next stage proceeds. It takes planning and patience but gives the tree a far better chance of surviving.

Practical Tips for Wollongong Homeowners

Plan tree placement carefully when planting new trees. Check mature size and root behaviour, and keep large species well away from buildings, pipes and boundaries. Mulch to a depth of around 5 to 10 centimetres to protect shallow feeder roots and retain moisture. Water deeply during dry spells, especially after any root disturbance. Avoid soil compaction from vehicles and heavy foot traffic over the root zone. And document the work, including photos and arborist reports, in case council or neighbours later raise questions.

Final Thoughts

You can cut tree roots without killing the tree, but the margin for error is smaller than many people think. Small roots on a healthy tree can often be removed safely, while large structural roots, excessive cutting or poor timing can lead to decline or instability, especially on Wollongong's slopes and in storm-prone conditions. Before picking up a saw, consider alternatives, check council requirements and get advice from a qualified local arborist. A short assessment now is usually far cheaper than losing a mature tree or dealing with a fallen one later.

Wollongong Tree Removal Pros

106 Gipps St, Wollongong NSW 2500

(02) 4210 5945