Most normal gardeners plant their plants in rows or even in huge fields with all one kind of crop, this is called monocropping. You'll drive down the road and see rows and rows, or entire fields of one crop, say corn. This is the worst way to grow crops. If a corn predator (bug, crow, disease) finds the cornfield, it will go from plant to plant destroying the entire crop, or most of it. If corn adverse weather comes it will kill the entire field or reduce the crop significantly. However, if the same farmer had planted several other plants with the corn, then possibly those would have survived the bug, crow, disease or adverse weather, as they weren't susceptible to it.
Permaculture has it's beliefs tied to the belief that monoculture planting is not the best way to garden. The belief is that if you plant as many different types of plants in an area, that some will survive no matter what happens. In permaculture you also lean toward planting as many permanent plants that you can in your polycultures. Permanent plants could be a canopy layer plant such as a tree, lower layer plants like shrubs, even lower plants like perennial and annual and biennial food and non food crops, but also below crops like fungi and even climbing plants like vines. Permaculture has lately been leaning toward edible or food forest gardens.
A food forest or edible forest garden trys to closly mimic the way nature grows things. You begin by planting your canopy layers, which could be a fruit or nut tree or even a shade tree (but why not try to grow as much food as you can ?). This canopy layer will support a lot of wildlife, bring in some shade, create humidity and provide mulch for the layers below it. Next you can grow lower growing trees such as a dwarf or naturally smaller tree, such as a plum or hazelnut tree, especially on the sunnier side of the canopy trees. Around these you can place plants that will support the life of the trees, such as a nitrogen fixing type plant that will feed your other plants nitrogen, dynamic accumulators which will bring nutrients up to the surface from deep within the soil by it's far reaching roots. You can also plant a variety of insectory plants, these will bring in your pollinators and your predatory insects (these will hunt down and kill the pests of your garden). It is best to have a large variety of insectory plants that will bloom from earliest spring to latest autumn.
Below these plants and around and among the food forest plants you should also consider as many food plants as you can find room for, especially those you have been buying from the grocery store, if they will grow in your area. Some people may even want to raise their own animal foods.
By building these food forests you will be bringing in a huge variety of food for your family, you may have excess to share with people or to feed to your animals, or even to feed to wildlife that will now want to visit your area. It takes very little land to build a food forest, you can even use dwarf or naturally small treees for your canopy layer if you only have a tiny yard. You can put a bench in the shade of the canopy to provide a more comfortable place for people too, or build a small arbor and put a grape vine up and over it fore more varities of food and even more shade.
The final area of the food forest to continue is also the fungi layer, in my food forest garden I have ground dwellling and tree dwelling fungi. Morel mushrooms would be an example of one that will grow in the soil, but there are also mushrooms like Shiitake and Lions Mane that you can grow on a log partially buried in your soil, or in a substrate of sawdust or straw bales.
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