Building Permanent Culture in Knoxville
Here is an idea for a guild of plants centered around an apple tree that can be used in a food forest. This comes from the book Gaia's Garden.
A guild is like companion planting, but uses more plants to build up the functions that are needed. Companion planting usually just consists of a pair of complementary plants.
For the apple tree guild, the center is (obviously) an apple tree.
Bulbs that do a good job of suppressing grass are planted in a ring just outside of the drip line of the trees - these keep the grass from encroaching in. These would include things like daffodil or garlic chives.
Mulch plants like comfrey and artichoke can be planted between these. These plants will be used to cut and drop to the ground as fertilizer.
Nutrient accumulators (these have deep roots that pull up nutrients below the line that most plants can reach) are planted beneath the tree; these include yarrow, chicory, or plantain. Most people would call these "weeds."
Insectary plants that draw in pollinators for the tree include dill, fennel, and bee balm.
Legumes can grow in the filtered / dappled sunlight under the branches. They will fix nitrogen and provide an additional edible crop.
Clover provides a ground cover between the other plants.
Notice that this guild includes a low tree layer, a herbaceous layer, and a ground cover layer. It could be more dense if you found a compatible vine to grow up the tree, or added mushrooms, or brought in shrubs close by. Try to find plants that don't need the exact same resources so they don't compete with each other - plants that have different light requirements or rooting depth.