What Happens When You Cut Tree Roots?
- Shelby Pietersen
- Jun 15, 2023
- 5 min read
Updated: Oct 15
Most people think of a tree as what they see above ground, trunk, branches, leaves. But half of a tree’s life happens out of sight. And when those roots are disturbed or cut, the effects ripple far beyond the soil.
Whether you’re dealing with roots lifting a driveway, blocking pipes, or creeping too close to a foundation, it’s important to know what’s really at stake before you dig.
1. The Role of Roots: The Hidden Half of Every Tree
Roots do far more than just hold a tree upright. They’re the tree’s lifeline.
Support and stability: Large structural roots act like anchor cables, keeping the tree steady against wind and slope.
Absorption: Tiny feeder roots near the soil surface pull in water and nutrients.
Storage: Many trees store sugars and energy in their roots to survive drought, heat, or pruning stress.
When you cut into that system, even accidentally, you’re cutting into the tree’s foundation, nutrition, and emergency reserves all at once.
2. What Actually Happens When You Cut Roots
a. The tree becomes less stable
Structural roots work like guy wires. When one or more are cut, the tree’s centre of balance shifts. It might not fall today, or even this season, but it’s now more vulnerable to heavy wind, rain, or saturated soil.
Tall or broad-canopied trees (like pines, oaks, or eucalyptus) are especially sensitive. A single deep trench or driveway excavation can remove key stabilising roots, leaving the tree leaning or uprooting after the next storm.
b. The tree goes into stress mode
Root pruning reduces a tree’s ability to draw water and nutrients. That means less fuel for photosynthesis, fewer reserves for growth, and slower recovery after seasonal changes.
You might notice:
Yellowing or dropping leaves
Smaller new growth
Early fruit or flower drop
Dead tips or dieback in the crown
This decline can take months or even years to show, making root damage one of the most underestimated causes of tree death.
c. Disease and pests move in
Fresh cuts underground are open wounds. Insects and soil fungi (like Armillaria root rot or Phytophthora) quickly exploit those wounds, especially in warm, moist soils.
Stressed trees release certain compounds that actually attract boring insects or beetles, nature’s cleanup crew responding to weakness. Once infection sets in, recovery is difficult without professional treatment or removal.
d. The soil ecosystem shifts
Healthy roots don’t just feed trees, they feed the soil itself. Roots release carbon compounds that nourish beneficial fungi and microbes. Cutting them disturbs this balance, reducing soil structure and moisture retention.
In compacted or disturbed sites (like driveways, trenches, or construction zones), the loss of root activity can turn living soil into hard, lifeless dirt.
3. Secondary Impacts Homeowners Often Don’t Expect
a. Structural instability and safety risks
Trees with major roots cut on one side are more likely to topple.
Even partial root loss can create a lever effect, where the next strong gust or saturated ground shifts the base just enough to start a lean.
Municipal bylaws and insurance policies often hold property owners responsible for failing to manage tree risk after root cutting.
b. Infrastructure damage doesn’t always stop
Ironically, cutting roots near walls or paving doesn’t always solve the problem long-term. When trees lose balance, new roots often regrow aggressively in the same direction seeking moisture, sometimes causing more upheaval than before.
A professional arborist can install root barriers or recommend selective pruning that reduces interference without destabilising the tree.
c. Environmental consequences
Every mature tree contributes to local carbon storage, air quality, and biodiversity. When trees die prematurely due to root damage, the loss extends beyond a single property.
Root systems also help regulate stormwater flow, stabilising slopes and preventing erosion. Cutting them increases runoff and soil wash during heavy rain.
4. How Much Root Cutting Is Too Much?
Every tree species and situation is different, but as a rule of thumb:
Losing more than 20–25% of the root system can seriously compromise tree health and stability.
Cutting within three times the trunk diameter (the “critical root zone”) risks destabilisation. For example, a tree with a 50 cm trunk diameter has a roughly 1.5 m critical radius to protect.
Older trees are far less tolerant than young ones.
Shallow-rooted species (like willows, gums, and poplars) react faster to disturbance.
A professional arborist can help map the critical root zone and identify safe pruning distances before any excavation or hardscaping.
5. Safer Alternatives to Root Cutting
Before you reach for the spade or saw, consider these options:
a. Install root barriers
Physical barriers made of thick plastic or geotextile fabric redirect roots downward or sideways without cutting them off completely.
These are ideal along new walls, paths, or plumbing lines.
b. Selective pruning instead of trenching
If roots must be pruned, target only the smallest possible section and cut cleanly with sharp tools. Rough tears invite decay. Never leave roots exposed, backfill with the original soil and water deeply afterward.
c. Structural soil or raised paving
In problem areas, build above the roots rather than through them. A permeable base or raised path lets oxygen and water reach the soil below while protecting infrastructure.
d. Ongoing tree care
Mulch generously (but not against the trunk), water during dry spells, and avoid compacting soil near the base. A healthy tree is far more resilient to root disturbance than one already stressed by drought or poor pruning.
6. When to Call a Professional
Root issues can be complex, especially when safety or property risk is involved.
A professional arborist can:
Assess whether the roots in question are structural or feeder roots
Determine the minimum safe distance for excavation
Recommend support systems or cabling if stability is compromised
Handle removal or pruning in line with local regulations and environmental laws
If the tree leans suddenly, loses foliage quickly after nearby digging, or starts showing fungal growth at the base, those are warning signs that warrant professional inspection.
7. The Bottom Line
Cutting tree roots is never a simple fix. It’s a trade-off between safety, infrastructure, and the long-term health of a living organism.
When done carelessly, it can destabilise the tree, open doors to disease, and lead to eventual failure, sometimes years later. When done thoughtfully, with proper guidance and aftercare, it can solve site conflicts without sacrificing tree health.
The difference comes down to planning, precision, and respect for how trees actually work.
Need expert advice before you dig? Our team uses the right equipment, respects the biology of each species, and leaves zero mess behind.
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