If you’ve ever wondered what is soil made of – GOOD!
You absolutely need to wonder about this kind of thing if you’re going to grow optimally healthy food.
Check out this video or read on below and you’ll see that many of our most important organic gardening tasks stem from this vital question.
And for more information on how to improve the nutrition and biological diversity of your soil, check out my organic fertilizing guide.
What Is Soil Made Of?
The usual story is that soil is basically a rather lifeless, static place for plant roots to sit and collect water and a few nutrients.
This would work okay if soil were a Magic grow toy, but it takes a lot more than N-P-K (nitrogen, phosphorus and potassium) to support the vibrant, living community that actually makes up healthy soil.
To understand what soil is made of, let’s start by answering the question of how does soil form?
How Does Soil Form?
It all starts with the bedrock or parent material. This gets broken down first by wind, water, temperature changes and chemical reactions.
This happens over thousands of years to create the beginnings of soil, but it’s still lifeless.
Then come the living organisms, the microorganisms and plants that work together to gradually turn lifeless dirt into a thriving ecosystem.
These organisms are the ticket! They’re a vital part of good organic soil, so I focus just as much on them as I do on nutrients in my teaching.
You’ll learn a lot more about them in the lessons to come since one of your main goals is ensuring you have enough of them and then making them happy.
So that’s the basics on the ‘how does soil form’ question – it’s created by environmental forces and by plants and other organisms. Now back to the first question – what is soil made of?
To get a picture of what makes up the basic mineral soil that our organisms are working with – the setting for our soil community – we need to understand soil texture.
There are three basic soil particle sizes: sand is the biggest, followed by silt (which is like sand but a lot smaller) and finally clay particles, which are WAY smaller and quite different from the first two.
Your soil texture refers to the relative amounts of these particles.
If you have mostly sand, you may have a sandy garden soil. If you have mostly silt or clay, you may have a silty garden soil or a clay garden soil. Ultimately, most soils are somewhere in the middle with names such as sandy loam or silty clay loam.
The quickest way to get a feel for your soil texture is to shape some moist soil into a ball, then try to roll that out into a cylinder. If it feels gritty and has a hard time holding a ball shape, you have a lot of sand.
But if that soil feels slippery and you can roll 1/3 cup of it into a tube more effortlessly than Dean Martin could roll a smoke, you can think about opening a pottery studio with all the clay you’ve got…
The soil texture from up above is the main factor in your soil structure.
Structure means how these individual granules clump together into globs of various shapes and sizes, or “aggregates”.
And then what that means for things like water and air movement, compaction, biological activity and root growth.
Knowing your soil texture and structure gives an important starting place for understanding how water and air will behave in your soil, which helps you make many important organic gardening decisions.
For example, a sandy soil will need watering much more often, but only a little water can be applied each time because most of it would just drain right through.
It also affects which organic fertilizers and soil amendments you should use and how much of them to use, and of course which plants will be most appropriate for your soil.
And remember how I said clay is different from silt and sand? The most important difference is that it’s the only one of these three soil particles that holds minerals in the soil, so having some clay is a very good thing…
But if you don’t have much clay, don’t worry – it turns out that organic matter is the real life of the party.
Many soil textbooks that answer the question ‘what is soil made of’ focus on the sand, silt and clay, and while these certainly are by far the most prominent part of the soil, a little bit of organic matter makes a world of difference.
Not only does organic matter beat even clay when it comes to holding onto nutrients, it also gives your soil better drainage, water-holding capacity, air-holding capacity, and resistance to compaction and erosion.
Increasing soil organic matter is another one of our main goals.
Your Role In Organic Soil Building
So if you’re wondering how does soil form, like how does really good vegetable garden soil form, that usually involves some input from us if we want it to be productive year after year.
In the end, the best way to turn bare dirt into nutritious soil is to provide what’s often lacking – balanced broad-spectrum nutrition, lots of varied organic matter, and a diverse group of soil microorganisms, too.
That’s what the next many lessons are going to be about.
Feel free to check out my fertilizing guide, or if you have any questions about soil, let me know below…