Ecosystems are often at their richest and most biodiverse and productive where one ecosystem meets another. In a broader sense, the interface between things is often where the most interesting events take place – where the soil meets the air, on the edge of water, the fringes of a forest. On a much smaller scale, we can use the 'edge effect' in a polytunnel by creating as many interesting edges, marginal spaces and points of interaction as possible.
One of the easiest ways to control the amount of 'edge' in your polytunnel is to think about the shapes and sizes of your raised beds or growing areas. Rather than creating two large growing areas with a path between, you may like to consider more, smaller raised beds, or creating interesting bed shapes – a flowing shape like a river edge, perhaps, or keyhole beds. Creating more organic bed shapes can sometimes help to create an organic edge effect.
Finding interesting ways to line your paths and growing areas, even when growing directly in the ground, can also help to maximise the amount and variety of edge in your polytunnel. Path edging with logs, stones or other natural items can help to define the boundaries, and is also a way of using edge to your advantage. Path edging and bed edging can add fertility (wood rotting, slowly, over time), or thermal mass to keep your polytunnel a little warmer (stone, clay etc.), or be useful to beneficial wildlife in your polytunnel. Planting right up to the edges of your beds will allow plants to take advantage of the improved (slightly warmer, or more moist for example) conditions and to thrive.
Maximising edge is not only about making the most of natural and human-made boundaries, it is also about valuing the edges and the marginal. The space in the top of the curve of your polytunnel is often wasted space – but you can make the most of every marginal inch by using vertical gardening techniques to make sure that you make the most of your polytunnel. The right staging, hanging baskets, making full use of crop bars and growing up cordons, canes and trellises are all options to help you make the most of each marginal space.
When developing layout and planting plans for your polytunnel, don't neglect any edges or marginal spaces. Making the most of your polytunnel involves making sure that you are utilising all of it as much as possible – including all the edges and marginal space.