The uppermost, fertile layer of soil (usually 6-12 inches deep) rich in organic matter and organisms, where most plant roots grow and where gardening occurs.
In plain terms
Topsoil is where gardening happens. It's dark, rich, alive with organisms, and full of nutrients and organic matter. It's formed over centuries by organism activity and organic matter accumulation. Good quality topsoil is gold for gardening. Poor topsoil (light-colored, compacted, lifeless) is a problem. Building topsoil through compost is the long-term solution.
Why this matters
Topsoil quality determines garden productivity. Understanding what makes good topsoil helps you improve yours and recognize good purchased topsoil.
In practice
Examples
Good topsoil: dark, crumbly, organism-rich; plants thrive.