Using 'Edge' in Garden Design Is Essential for Boosting Biodiversity—Here's How to Do It

In permaculture design, we often talk about using edges. But this can be a confusing concept for those who are not necessarily very familiar with permaculture ideas. When we talk about using edge or maximizing edge, what we are really talking about are the ecotones between two distinct ecosystem types. Here is some more information to demystify the concept for those who are not already aware of the general ideas involved.  

What Is an Ecotone?

An ecotone is a boundary between two ecosystem types or biological communities. For example, the boundary between a forest or woodland and open grassland, or where terrestrial ecosystems meet aquatic or marine environments.

These boundaries may be hard divisions, where one ecosystem type suddenly transitions to the next, or blurred boundaries where one ecosystem gradually transitions into another. 

These marginal or edge areas where one type of ecosystem blends into another can often be the areas that are richest in species diversity. 

Why Edge Is Important

We talk about maximizing edge in permaculture design because one of our key goals is to make the most of biodiversity—not simply in terms of species numbers, but in terms of the number of beneficial interactions between species. The more beneficial interactions there are between the elements in a system, the more stable and resilient that system will be. 

So by maximizing edge areas, where one type of environment of vegetation type transitions to another, permaculture designers will seek to increase the stability and resilience of the system. 

Edges are places where you will find species from two distinct ecosystem types, plus new species allowed to thrive due to the unique environmental conditions created by the merging of the species from both ecosystem types. 

Say, for example, a woodland environment supports species A, B, and C. And grassland supports species D, E, and F. An ecotone between the two might support A-F, plus G, H, and I (due to increased light levels, higher water availability, or other environmental factors). 

Perhaps this makes it a little easier to understand why edge is so important when it comes to increasing biodiversity in a garden. If you look at the edges of a woodland or forest, the riparian zone along a river, or other natural examples, you will find it easier to understand this "edge effect." 

Using Edges in Garden Design

Using edges in garden design simply involves making use of this natural phenomenon to increase the biodiversity and productivity in a garden. 

Thinking about the shapes of beds and borders, pathways, ponds, and other features in garden design can help us to maximize the amount of edge environment we can create. For example, rather than making straight paths, we can create winding paths that have edges far longer in length. 

We can create food forests or woodland gardens with meandering edges, perhaps contouring the edge of the system to create sun traps to the south (in the northern hemisphere) where plants that like mild and sheltered conditions can flourish. 

We can create hedgerows and other planting schemes between garden zones, breaking up the space and creating a range of new microclimates and growing conditions. 

We can make beds in irregular or curving, wavy shapes, or with a keyhole design, rather than sticking with single rectangular growing areas or borders with straight lines. Or can include more, smaller beds rather than fewer larger ones. 

And by staggering planting to make zigzag rows rather than straight lines, we can maximize the number of plants that can be included in a growing area. 

Using patterns from nature can help us understand how edge can be maximized. One key example of this is the spiral form. This is commonly used, for example, in creating a "herb spiral"—a concept that allows a range of herbs that like different conditions to be grown in a smaller area. In a cone-shaped form, this concept maximizes both growing area and edge, creating a range of different microclimates. 

In the same amount of space, you can create a pond with curving, sinuous sides which have far more edge than a simple circular pond. 

There are plenty more examples, but the above shows that what is useful to understand in larger-scale natural systems can also be helpful in designing a garden. 

Using edges and valuing the productive and abundant boundaries between different biological communities can help us make the most of the space available in our gardens, and help us mimic nature and garden in a more sustainable and eco-friendly way.