Observation is a key element of permaculture design, and plants can help us to understand the landscape under our feet.
Indicator plants are plants that grow in such a density that their success in out-competing other plants can tell us a lot about the soil and microclimate they grow in. Several means can be used to link a plant with a bio-indication: primary ecological range, ecological niche, characteristics (physical , chemical, etc.).
For example, a plant with a strong tap root has an advantage over other plants in a compacted soil. A nitrogen-fixing plant can thrive in a nitrogen-poor environment. The beauty of nature is that this process creates an homeostasis, leading to fertile soils — the tap-rooted plant decompacts the soil and the nitrogen-fixing plant makes nitrogen available to nearby plants via roots or leaves.
French-speaking European permaculturists can use the two-volumes encyclopedia of bio-indicator plants written by Gérard Ducerf, that indicates bio-indication from over 500 common plants of Europe.
As we just acquired our 1.3 ha (3 acre) property, this book is a precious guide during our observation phase. For example, a small stall and a kennel are located not far from the house. As you can see in the picture above, two species of plants are clearly bio-indicators of something.
After identification, the plants in front of the kennel (left) are Golden Parsley (Chaerophyllum aureum) and those in front of the stall (right) are Dwarf Elder (Sambucus ebulus). As reported by Ducerf, both are indicators of soils saturated with water and/or OM (organic matter). This is not a surprise, as there were two goats and two donkeys before we moved in. The animals would have eroded the soil (top of the picture), compacted it under their hooves (thus the water-logging), and dropped large amounts of OM.This is in part why we asked the preceding owners to give the animals away before we moved in, in view of the steepness of the landscape.
Bio-indicators can tell the history of the landscape, but they can also be a tool to choose what to do next (often to restore ecological health before it is too late). Of course this is just an element among others, as it depends on other factors (such as zones and sectors). But let’s play a little with the Dwarf Elders. They seem not very useful ‘as is’ and they are located not far from the house (between zones 1 and 2) on one of the rare flat areas of the landscape. In the encyclopedia, it is said that Dwarf Elder is a plant that like nitrate. So, we should succeed in growing (according to zone) plants that thrive on plenty of water, OM and nitrates. After asking a garden-geek friend of mine, such vegetables are corn, spinach, cabbage and squash. So, what about growing a “two-sisters” polyculture of corn and squash?
Nature is so powerful that you can read the past, and sometimes the future just by looking at plants!