The Zone of Influence: Essential Considerations for Designing Landscapes

When creating new garden spaces, whether it's terraces, retaining walls, or garden beds, one often overlooked but crucial factor is the "zone of influence." In engineering and construction, this term refers to the area affected by any physical changes made to the landscape, and it plays a significant role in the success of your garden design. Without accounting for the zone of influence, even the most aesthetically pleasing design may run into problems with stability, water movement, or plant health.

Let’s explore why understanding this concept is essential when shaping landscapes.

1. Terracing and Level Changes

Terracing a garden or changing its levels can significantly alter how water moves across the landscape, which in turn affects plant growth, soil stability, and drainage. The zone of influence around any terrace includes not just the immediate area but also the slope above and below it, where erosion or water runoff could occur.

When creating terraces, it’s essential to account for:

• Soil stability: Changes in elevation alter how soil behaves under weight and moisture. The load from a terrace can shift soil further downslope, affecting areas below it.

• Water movement: Water collects differently around terraces, which can lead to pooling in lower areas. Adequate drainage systems must be designed to mitigate this impact.

• Vegetation influence: Root systems of nearby plants can extend beyond their visible growth area, impacting the stability of your terraces.

By accounting for the zone of influence in your terracing design, you ensure that the structural integrity and environmental balance of the landscape remain intact over time.

2. Retaining Walls and Their Impact

Retaining walls are essential for stabilising soil in sloped areas, but their zone of influence extends well beyond the physical footprint of the wall itself. The wall bears the pressure of the soil it holds back, but the surrounding soil and any nearby structures are also affected.

Considerations when designing retaining walls include:

• Lateral soil pressure: Retaining walls need to be designed to withstand the horizontal force of the soil. The zone of influence here includes the area above and behind the wall, where soil movement or water pressure can impact its stability.

• Drainage: Poor drainage behind a retaining wall can lead to water build-up, increasing the lateral load. Integrating weep holes or drainage pipes prevents excessive pressure on the wall and protects surrounding garden areas from waterlogging.

• Root zones: Trees or large shrubs near retaining walls need special consideration, as their roots can exert pressure on the structure or compromise its integrity over time.

Ensuring that the design accounts for the full zone of influence around retaining walls protects your garden from future structural issues and maintains the safety of the space.

3. Garden Beds and Water Flow

The placement and design of garden beds are not just about aesthetics—they also influence water movement, soil health, and the success of your plants. The zone of influence for garden beds is largely related to water distribution, root growth, and soil nutrients.

Some key factors to consider include:

• Water movement: Raised beds, for example, change the flow of water across a garden. Water can pool around the edges or run off too quickly, affecting nearby plants. Proper irrigation and grading of the surrounding area help balance the moisture levels within and around your garden beds.

• Soil compaction: The weight of garden beds, especially raised or terraced ones, can compact the soil underneath them and affect nearby plants’ root systems. Loosening soil in the zone of influence ensures that roots can spread without restriction.

• Plant root zones: The roots of plants within garden beds may extend beyond the bed itself, impacting nearby spaces. It’s important to leave sufficient room for root systems to develop and thrive without competition from neighboring plants or structures.

By thinking ahead and understanding how the zone of influence affects your garden beds, you can create a more harmonious space where water, soil, and plants work together effectively.

Designing with the Zone of Influence in Mind

When designing or constructing any landscape feature, whether it's a terrace, retaining wall, or garden bed, the zone of influence must be considered to create sustainable, safe, and beautiful outdoor spaces. Understanding how soil, water, and plant systems interact beyond the immediate structure will lead to more resilient landscapes that stand the test of time.

In all of my designs at Wild Gardening, I prioritise a thorough understanding of these unseen forces to ensure our projects deliver not just aesthetic beauty, but also longevity and functionality.

When it comes to creating mesmerising outdoor spaces that harmonise with the natural world, look no further than a pioneering landscape architecture and design studio nestled in the Northern Rivers region.