Most biologists, (says Vogel, 1981) seem to have heard of the boundary layer, but they have a fuzzy notion that it is a discrete region, rather than the discrete notion that it is a fuzzy region.-Bill Mollison “Permaculture: A Designer’s Manual”
I think the textbook term “edge effect” is often mistaken. We read edge is where the most energy is at work and the typical response is to make a lot of wonky lines and curved keyhole beds so our system has lots of energy at work simply by design. This approach has its benefits, but when you have a garden border against encroaching grass and other weeds, as is typical, more edge only makes for more encroaching grass, making the only noticeable energy at work you weeding.
This is using edge effect –nature using edge effect, not you. To turn things on head we must do a little thinking (pun intended), and in the case of garden beds, make our edge the growing edge, the grass and weeds the shrinking one.
One way is by making the bed edge a growing edge. Keep mulching out, as I explain here. To simply maintain a new bed, I mow next to it with my scythe’s grass-carrying stroke moving toward it. This way the last bit of the stroke slips under the mulch chopping off the few straggler grasses, stuffing the grass I just cut for several feet from the side underneath.
With the right choice of species, raspberries, mints, strawberries, many kinds of clover, and self seeding annuals and perennials will follow — or even speed ahead of this expanding edge –with a storm of growth. This is the function most of these plants serve in natural woodlands; and as such they are supposed to die off as they use up nutrients and get shaded by the woody plants they’ve made way for.
Think of it as another wave of growth when we follow, sticking woody trees and shrubs into this new herbaceous layer.
Here, if we just keep one step ahead of the game, and figure placement for plant species that are really different from one another in root growth, there are a lot of available edges we can use among the plants.
For instance a taprooted plant next to a fibrous, shallow rooted plant. Using soil the other can’t reach, these roots are on the edge of each other. Do the same with tops, choosing plants that vary in height, and you get the same thing with light exposure.
Once everything is established, a fourth, reoccurring edge appears –for instance comfrey you cut several times a year, or with nitrogen fixers you cut once or every couple of years. This cutting makes a hole all around the edge of the plant in which something else can temporarily grow.
With nitrogen fixers such as amorpha, the best time to coppice is the best time to plant out tomatoes started indoors –just past danger of frost. The amorpha will be sloughing off a lot of nitrogen-rich roots in the now empty space around it, so the tomato will not only have space, it will get quite a flush of nitrogen to make it grow.
Even with the quickest growing plant, comfrey, you can harvest mache (Valerianella locusta). Plant the mache in fall and let it grow up through winter and early spring. By time the comfrey has made much growth the mache has already been harvested, and any left are half way through making seed. The comfrey will only serve to protect the falling seed from sun and birds. The mache and comfrey perpetuating this cycle ad infinitum.
So there you have edges in the garden to edges in species to edges in time and a few ways to use them. Believe me though, there are more. Just give it some thought.