As humankind cannot live alone, so the plants and animals; every living being evolved with companions and guilds as they support each other in many different ways. This social interaction endorses the resiliency of the entire community from a holistic point of view.
Plants have companions for many different reasons. Sometimes we see these, and sometimes they are microscopic.
A good soil where food crop is growing should have a balance of bacteria and mushrooms. While some plants favour more of the bacteria, some plants favour mycorrhiza. Some plants don’t like both and only prefer certain other plants.
Bacterially dominated soils growing pioneer herbaceous plants may become food to mushrooms in the future laying the foundation for trees and shrubs. If there were no humans on the planet, eventually it would have covered with forests.
A symbiotic relationship between two or more species develops throughout the evolution of those species. They depend on each other to utilise the resources and waste created. Plants create sugars out of photosynthesis and trades with mycorrhiza in the root zone to get minerals in return. Mycorrhiza cannot live while exposed to the sun but still gets the benefit of it from the plant above. Most plants can not dissolve rocks to consume the minerals in water-soluble form but mycorrhiza can. We don’t exactly know when and how they’ve found each other, but there was a perfect environment for a relationship to flourish.
You might have seen the article about plants talking to each other using the mycorrhiza network in the root zone. All the chemicals and hormones plants create roams in this network. For example, when a plant is attacked by a bug, releases certain hormones in the root zone. If there were enough organic material in the soil, the mycorrhiza network would be already developed carrying the hormones from plant to plant. The other plant that is not attacked yet can then release the hormones in advance deterring the bugs.
Plants with a strong scent like nasturtiums, mint, oregano, thyme, perpetual basil, mustard, garlic, walking onion, perennial leek, horseradish are used to deter borers and suckers. Some of these also control root nematodes and support soil integrity.
Sweet plants like corn, broad beans, adzuki beans, snap beans, clover, rye, wheat, soybeans support the mycorrhiza network and fix nitrogen from the atmosphere into the soil. Perennials like Scottish broom Cytisus scoparius and Tagasaste Cytisus proliferus would be permanent nitrogen fixers in a permanent food forest. There are many other nitrogen fixer plants which you can incorporate into your garden. This fixed nitrogen in the soil will be used later by the other plants as a fertiliser.
If you are using a nitrogen-rich fertiliser and over do it, you will start to see aphids and probably leaf curl that comes with it. As soon as you see aphids, you may think of buying and releasing ladybugs to get rid of the aphids, but this is not a solution to the real cause. Reducing nitrogen fertilisers would have been much more economical.
This Excel file is the most comprehensive list of companions on the net.
A guild is specifically designed based on deficiencies in the soil, so a soil test is a must to understand what is missing and build a guild using companion plants and certain neutral plants to address missing minerals. Tap-rooted herbaceous plants mine deeper soils to pull minerals like dandelion, comfrey, fennel, milk parsley, sea holy, coltsfoot. Growing these outside the tree’s drip line and mulching chop-n’drop style under the tree would be beneficial.
Guilds are usually designed for perennials to establish long-term relationships and managed throughout the life of the guild adding or removing helpers around the central plant.
Guilds may sometimes include neutral plants to provide certain minerals. Like a goji berry to provide potassium in a fig guild. I call them neutrals as they are neither in the companion category nor anti-beneficial like snow peas and garlic.
To build the guild, you start with companions and according to the missing minerals, find other shrubs and plants to help the central plant.
Lyneham Commons in Canberra has guilds designed for golden delicious apple, somerset red streak apple, cherry, sour Kentish cherry, fig and mulberry with excellent explanations as to why specific plants are chosen.
The Excel sheet below is a list of dynamic accumulator plants. Once you know what mineral is missing in your soil, you might want to grow some of these plants to mine the minerals and use them as mulch under your trees or where they are required like compost or weed teas.