Regolith

Unless you are using hydroponics, all of your plants will grow in some sort of soil. The better we understand our soil, the easier it will be for us to take good care of it (and easier is good).


Soil tends to form layers on top of bedrock. These layers of soil are called horizons. Just above the bedrock is a layer of unbroken rock. There are generally no plant roots here. This is called the regolith. 


The infographic below shows the basic soil horizons:

(UCANR)

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The U.S. Department of Agriculture has an amazing interactive map that can help you learn more about your local soil.