By Diane C. Kennedy.
Permaculture encompasses methods of gardening, horticulture and agriculture based on observations of nature. While that sounds very prosaic, if you observe the functions of plants and their interactions with weather and animals, you can use these lessons for growing. In this way you are practicing regenerative land use.
One lesson from nature is that every plant has a particular function, and they arrange themselves opportunistically in patterns where there are symbiotic relationships along with competitive ones. Permaculturalists call these patterns plant guilds.
The first plant type in a guild is the canopy. That would be the tallest plant in the biome. Its role is to be the first and usually longest-lasting protection of the soil from harsh weather conditions. The leaves shade out the harsh summer sun, they break the trajectory of hard rain so the drops hit the leaves, shatter into many slower-moving smaller droplets, and provide nesting and perching places for larger predatory birds. In a forest the canopy plant can be large tree such as oak; in an orchard it can be a fruit tree, or in a garden a staked tomato plant.
Next is the sub-canopy, which takes a similar role to the canopy. It often breaks up the rain droplets that the canopy has already shattered, and further decelerates and breaks them up. Sub-canopy is strong enough to hold sturdy vines, is a place where mid-sized birds and animals live, and helps to capture humidity. Both canopy and sub-canopy also help modify and humidify wind, and protect the smaller plants below.
Groundcover plants sprawl across the soil, protecting it from compaction and sun, creating safe habitat and food for a wide range of animals, and flowering to attract beneficial insects and pollinators. Rain droplets slide off their leaves and saturate the soil without creating compaction or erosion.
Vines also protect the ground and can protect exposed tree trunks from sun scald by twining around them. Squash is one of the ‘three sister’ crops, and its large leaves not only provide protection from the sun, but also protects the corn (another sister) from raccoons, which are loathe to walk through a sea of vines. Vines also flower to attract pollinators.
Nitrogen-fixing plants are those which have a symbiotic relationship with certain bacteria in the soil, harvesting nitrogen from the air and affixing it into nodules on their roots. When the roots die the nitrogen is released into the soil. Legumes are all nitrogen-fixers, as well as other plants such as Ceanothus (California Lilac). Allowing these plants to grow and then cutting them at their base without removing their roots harvests the nitrogen, so don’t pull up your pea and bean plants.
Lastly are the deep-rooting mining plants. These plants break up hard soils with their deep roots, which then mine minerals from deep into the soil and deliver them to their leaves. When the leaves die, the minerals are transferred to the topsoil. Removing the tops from your carrots and leaving them on the soil, or growing comfrey and artichokes and using their tops as green manure helps hasten this cycle.
The earth is always trying to build, protect and repair topsoil. All the plants are geared toward adding organic matter to the top several feet of earth. The combination of plants creates habitat for a tremendously wide range of animals and insects, all essential for healthy ecosystems. The earth isn’t on a human-scale timetable so soil building takes a long time. However, if we understand what the plants are doing, we can arrange them into guilds in our gardens, let them get on with their jobs, and help them build the soil for us in our faster time scale, without the use of chemicals.