Understanding soil

The best way to define soil is to call it an ecosystem where dead matter (clay, sand, rock, organic matter …) and an abundance of living matter (microorganisms, fungi, earthworms, insects …) interact with each other.

Plants find their way into this enriched soil with the help of their branching roots, always looking for water and nutrients. Understanding the material your dealing with is a big part of organic gardening.

The many types of soil

You’ve probably come across the terms clay and sandy soils. But what does this actually mean? The particles in soil used to be part of rocks. These rocks were exposed to certain weather conditions and chemical reactions (wind, heat, cold, water …) and broke down into smaller pieces or particles. Soils are given names based on the particle size, which are clay (less than 0,002 mm), silt (0,002 – 0,063 mm) and sand (0,063 – 2 mm).

When there’s a majority of a certain particle size, we call it by that name. A fixed ratio between these mineral constituents can have a name as well, like loam. However most soils are a mix of different particles and therefore have mixed names like clay silt loam or sandy loam. The mixture of these particles forms what we call soil texture.

How to determine your soil texture

You can do a quick test to see what kind of soil type you have. Take a handful of soil, add some water to it and try to make shapes with it.

  1. Shape keeps falling apart? SAND
    Sand is lightweight, contains few nutrients and doesn’t hold enough water. Heats up easily in springtime.
  2. Cylinder without cracks? SILT
    Very similar to clay, but less distinct
  3. Circle? CLAY
    Clay is heavy, contains many nutrients and easily holds water. Heats up slowly in springtime.

Once you know what kind of soil your garden exists of, you can start using this to your advantage. You’ll have a better understanding of your garden’s successes and failures. You’ll be able to give it what it needs and you’ll know how to work your way around its lesser qualities.

The importance of organic matter

Organic matter exists of dead animals, plants and other organisms. It’s a continuous cycle of adding matter and breaking it down into useful nutrition for a variety of living organisms. Although it’s just a small amount of the total soil mass, its presence is vital for your crops.

Earthworm in Compost

In time, organic matter is broken down by small living organisms into mineral nutrients, CO2, water and a stable form of leftovers, called humus. Humus is the glue between the rock particles and everything else, creating a fine crumbly structure. It retains a big amount of water and nutrients which in time is handed off to plants. It’s there that humus can make a big difference to the quality of your soil, especially sandy soils. Its dark color also guarantees a faster warming up in springtime.

Micro- and macro-organisms

Next to dead matter, there are also a lot of living organisms active in your soil. Some of them can be observed with the naked eye, for others you’d need a microscope.

Micro-organisms are a group of organisms existing out of bacteria, fungi, algae … These are further subdivided in smaller groups. Macro-organisms are those we can observe with the naked eye like larvae, snails, mites, worms … The most useful of macro-organisms in our garden are earthworms. Digging tunnels whilst processing matter they create an open and loose upper layer of soil, perfect for plant roots. I’ll write more about earthworms in a future post.


Water is a necessity for plants. Plants need water for the obvious reason that it’s one of its building blocks, but also because water is a transport device for nutrients.

During rainfall, the macropores of your soil get filled to a certain amount. After saturation, it seeps further down to groundwater levels. That’s when your soil reaches its water-bearing capacity. Leftover water is kept in your soil’s micropores by soil particles, available for living organisms. At a certain point, those soil particles will detain the water at a force that makes it impossible for the roots of your plants to obtain it. That’s when dehydration occurs.


Last but not least is the presence of air inside your soil mass. There should be a well-balanced amount of water and air in the ground.

The air inside your soil almost exists out of the same composition as the air in the atmosphere. The biggest difference is the humidity and larger amount of CO2. The reason for this extra amount of CO2 is the breathing of living organisms in the ground and the decomposition of organic matter.



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