Growth Limit Zones

How the rules apply

The regulations use several zones around power lines. These zones help determine when trees must be trimmed, when notices can be issued, and what restrictions apply.

Trees growing too close to a power line

Growth Limit Zone

The space immediately around a power line that must be kept clear of vegetation. The size and shape of the growth limit zone depends on the voltage of the line and, in some cases, the span length of the line.

Cut-back Zone

This extends 1 metre out from the growth limit zone. If a tree is growing into the growth limit zone, it needs to be trimmed back far enough to reach the cut-back zone unless a dispensation applies.

Hazard Warning Zone

This extends 2 metres out from the growth limit zone. If vegetation enters this zone, we may issue a hazard warning notice to alert the tree owner.

If a tree qualifies for its first cut or trim under the regulations, we will pay for that work. After that, keeping the tree clear of the power line — and paying for any trimming that’s needed — is the tree owner’s responsibility.

Different rules can apply in some circumstances, so check with us if you’re unsure.

Trees that could fall into a power line

The treefall hazard zone is an area that extends 24 metres from the growth limit zone.

Trees within this zone may be assessed by a lines company. This does not mean every tree in the zone is a hazard. It means the tree may be assessed if there is concern that, because of its condition, size or location, it could fall onto the power line. A formal treefall hazard notice can only be issued if the tree is assessed as a moderate or high hazard.

Treefall hazard notices will not be issued before 23 July 2028. Before then, we may use voluntary processes to discuss hazardous trees with tree owners. These voluntary processes are separate from the formal treefall hazard notice power in the regulations.

Planting a new tree near

On 23 July 2027, a low height planting rule comes into effect. This means you must not plant a tree if you reasonably expect it could grow taller than its distance from the power line.

The low height planting zone extends 24 metres horizontally from the power line. 

If you plant a tree in breach of this rule: 

• you may be liable for damages
• you may be responsible for the cost if the tree later needs to be cut, trimmed or removed
• you cannot use a ‘no-interest’ tree notice to transfer responsibility for managing the tree to the lines company.  

The planting restriction does not apply to trees that grow naturally. However, if a self-sown tree within the low height planting zone later needs to be cut, trimmed or removed, the tree owner may be responsible for the cost. 

There are some exceptions. The low height planting zone does not apply: 

• on existing forest land
• in urban areas
• to shelterbelts
• on land administered under the Conservation Act 1987. 

Not sure whether your property is in an urban area? Check your district plan or contact your local council. 

If you're planting near power lines, think about how tall the tree is likely to grow over time. 

From 23 July 2027, planting restrictions will apply in the low height planting zone outside urban areas, outside existing forest land, and except for shelterbelts and land administered under the Conservation Act 1987. 

Check our planting guide for more details: Unison Planting Guide

Vegetation growing above the line – ‘clear to the sky’

For some power lines, the growth limit zone extends vertically above the line as well as around it. This is known as ‘clear to the sky’ and means vegetation must also be kept clear above the line. 

Clear to the sky already applies to higher-voltage lines in both urban and non-urban areas. From 17 October 2026, it will also apply to lines at 11 kV or below outside urban areas. 

What happens if a tree grows too close to a line?