Paul Wheaton and Jocelyn Campbell review Gaia's Garden the second part of Chapter 8, by Toby Hemenway. The chapter is called: Creating Communities for the Garden, and it addresses polyculture. He shares what he would plant in his apple tree guild. What you're trying to do is: lure beneficial insects, boost soil tilth and fertility, reduce root competitions, conserve water, balance fungus populations, diversify the yield of food, and create habitat. Creating the guild "reduces the gardeners load to the broad back of nature."
Toby recommends a ring of grass supressing bulbs along the drip line of the tree, which surround flowering and food producing plants. Paul expresses his frustration with the question, "What do I plant under my apple tree?" as the answer depends on everyone's unique circumstances. Grass is a nutrient pig and will leave nothing for the tree. Toby says the tree should be pruned to an open shape to let light into the plants below. Paul prefers not to ever prunetrees. Paul talks about the importance of edge, and how nature takes things to the next level over the years by herself--our job is to get the understory beyond being just grass.
He and Jocelyn then discuss the importance of accumulator plants, nitrogen fixers, pest repellants, and habitat nooks (stones, logs, brush, and small ponds) for critters like snakes, lizards, and frogs. Rocks stay cool around the base of the tree and condense water for it, and rocks around the dripline hold thermal inertia. Paul talks about the value of comfrey. He and Jocelyn talk about harvesting your own mulch, such as with the chop and drop method.