What is Soil Made Of?

What is soil made of? Funny you should ask. After all, GrowingAnything.com wouldn’t exist if it weren’t for the stuff.

Technically there are over 100 types of soil that are classified into orders, groups and sub-groups along with multiple layers of soil as you dig further into the earth. Rather than getting all scientific on you, let’s assume you’re interested in good ole run-of-the-mill healthy plant-growable topsoil…

Generally speaking, soil is made up of old rocks (45%), old organic material (5%), air (25%) and water (25%). Both the rocks and the organic material that make up your soil have been broken down and gradually mixed together over time through natural processes such as erosion, weathering and decomposition.

Original Vs. Secondary Minerals

Soil minerals can be divided into two groups: Original minerals that form rock from cooling magma and secondary minerals that are cemented together to form sedimentary rock. Click here for the full list of each type.

The types of old rocks that contributed to the soil’s current makeup, the minerals they contained and how much they have broken down will largely determine the appearance (color) and texture of the soil. The width of the rock particles determines whether the soil is called sand, silt, clay or a combination of the three:

  • Clay particles are the finest at less than 0.002 millimeters
  • Silt is in the middle at between 0.002 mm and 0.05 mm
  • Sand is the largest particle at between 0.05 mm and 2 mm

Want to learn more about soil microorganisms? Check out this page.

More importantly than old rocks (to your and my existence, anyway), just a handful of healthy soil is also made up of billions (with a ‘B’) of thousands of types of microorganisms. These microorganisms, including a wide variety of fungi and bacteria, break down organic (plant and animal) matter so that the soil’s nutrients become small enough to be used by plant roots.

Without those microorganisms breaking down the nutrients to a usable form, the cycle of life would be stopped in its tracks.

Let’s continue the discussion on our Why is Soil So Important? page.

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