A retaining wall that doubles as a garden planter is a smart way to manage a sloped section while adding greenery and structure to your outdoor space. With good planning, the right materials, and attention to drainage, many NZ homeowners can tackle a modest version themselves — but there are important rules around height and consents you need to know before you start.
Plan Before You Dig
The first step is understanding what you're actually building. A combination retaining-planter wall holds back soil on one side while creating a raised garden bed on the other (or on top). This means the wall faces two sources of soil pressure and moisture, so it needs to be built more robustly than a simple garden edging.
Key planning questions:
- How high will the wall be? In New Zealand, retaining walls over 1.5 metres in height generally require a building consent. Some councils have lower thresholds, especially on unstable ground or near boundaries. Always confirm with your local council before starting — check MBIE Building Performance for guidance on Schedule 1 exemptions.
- What's the soil like? Clay-heavy soils (common in Auckland and Waikato) retain water and exert more pressure. Sandy or free-draining soils are more forgiving.
- Are there any services underground? Contact Dial Before You Dig (0800 248 344) to locate buried pipes and cables.
- Is the wall near a boundary or structure? This can affect consent requirements and setbacks.
Choosing Your Materials
The material you choose affects the look, cost, and complexity of the build. Common options in NZ include:
| Material | Pros | Cons |
|---|---|---|
| Concrete blocks (e.g. Besser blocks) | Strong, durable, widely available | Heavy, may need mortar or reinforcing |
| Timber sleepers (H5 treated pine) | Easy to work with, natural look | Can rot over time, check treatment rating |
| Natural stone | Attractive, long-lasting | Expensive, labour-intensive |
| Segmental retaining blocks | Interlocking, no mortar needed | Limited height without engineering |
For a planter wall, H5 treated timber sleepers are popular because they're easy to cut and stack. Make sure any timber in contact with soil carries the correct hazard class rating — H5 is the minimum for in-ground contact. You'll find treated sleepers at Bunnings, Mitre 10, and PlaceMakers.
Step-by-Step: Building a Timber Sleeper Planter Wall
This guide covers a simple single-tier wall up to around 600–900 mm high, which is generally exempt from consent (confirm with your council).
1. Mark Out and Excavate
Mark the wall line with string and pegs. Excavate a trench about 150–200 mm deep for your first course of sleepers — this buried base gives stability.
2. Lay the First Course
Place your first sleepers in the trench, checking they're level. This base course is the most important — take your time here.
3. Stack and Stagger
Stack subsequent courses with staggered joints (like brickwork) for strength. Secure each course with galvanised rebar or coach screws driven through into the course below. Use at least 150 mm coach screws.
4. Install Deadman Anchors (if needed)
For walls over 600 mm or holding significant soil, install deadman anchors — horizontal sleeper sections running back into the slope at regular intervals. These resist the wall tipping forward under soil pressure.
5. Drainage Is Critical
Poor drainage is the number one cause of retaining wall failure. Behind the wall, lay a 100 mm perforated ag pipe wrapped in geotextile fabric, sloping to an outlet. Backfill with free-draining gravel (at least 300 mm) before adding topsoil. BRANZ has useful guidance on drainage best practice.
6. Line the Planter Section
If using timber, line the inside of the planter with geotextile fabric (not plastic — you need drainage) to protect the wood and keep soil from washing through gaps.
7. Fill and Plant
Fill with quality garden mix or a blend of topsoil and compost. Leave a gap of at least 50 mm below the top of the wall to allow for watering without overflow.
Drainage: Don't Skip This Step
Drainage is the most important part of any retaining wall build. Water trapped behind a wall dramatically increases soil pressure and can cause the wall to fail — sometimes suddenly. Always:
- Use free-draining backfill (crushed rock or gravel)
- Install ag pipe at the base of the wall
- Ensure the outlet directs water away from foundations and boundaries
- Avoid directing runoff onto a neighbour's property (this can be a legal issue)
Choosing Plants for Your Planter Wall
Choose plants suited to the aspect (sun or shade) and your region's climate. Shallow-rooted plants like herbs, succulents, strawberries, and low-growing perennials work well in raised planter walls. Avoid large trees or shrubs whose roots could destabilise the wall over time.
When to Call a Professional
You should engage a qualified retaining wall builder or structural engineer if:
- The wall will be over 1.0–1.5 metres high (check your council's threshold)
- The site has unstable, expansive, or waterlogged soil
- The wall is near a boundary, building, or driveway
- You're on a steep slope or the wall is tiered
- A building consent is required — consented work must be carried out or supervised by a Licensed Building Practitioner (LBP)
For anything beyond a modest garden planter wall, getting a professional involved protects your property and your neighbours. You can find experienced local retaining wall builders on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
