Just a single teaspoon of soil can contain millions of tiny organisms with more than ten thousand different species.
Although they are vital for maintaining healthy human life, we still know relatively little about them.
Soil is far more than a simple growing medium for plants.
Healthy soil is actually a highly complex living entity composed of innumerable living organisms. Life underground is highly sophisticated. It’s strongly linked to all living processes.
The core purpose of the huge variety of subterranean life is to break down organic matter so that plants can access it easily. This process kicks off with small and visible creatures like worms or slugs. They digest large pieces of waste material with ease. The organic matter is reduced drastically in size into far smaller particles with an enhanced surface area.
Bacteria, minerals and fungi mix in with this and everything is taken down below the surface. Here, it is once again digested at a microbiological level. The bacteria in the soil are largely responsible for this.
Soil harbors many different types of bacteria. These bacteria optimize the contents of organic matter for growing plants.
Some bacteria secrete enzymes that will bind together the soil particles. This means that they can take on some structure and form clumps.
Other bacteria break down molecules to make them more easily accessible to a broader range of plants.
Protozoa feed off both fungi and bacteria. They release nitrogen into the soil and excrete waste material in turn. When the bacteria and fungi die, they decay and contribute in their own way by releasing minerals into the soil.
In the garden, every single aspect of things intertwines. The destruction of even one tiny pest can diminish the whole balance.
Many farmers across the western world have shifted from using organic matter and replaced this with artificial fertilizers. These chemicals can alter the complicated natural balance. Soil can become sadly lifeless. Most of the huge range of micro-organisms are killed off. When this happens, the soil stops being able to recycle organic matter or to release nutrients. Resultantly, crops lessen in size and become less resilient at resisting disease. There is then the need for increasingly more chemicals which worsens the situation further. It’s a vicious circle.
The important lesson to learn from these undesirable changes in balance is that we really need to cherish and value our precious soil.
Layers Of Soil
This is the basic type of soil.
Subsoil forms a layer above the underlying rock. This can be just a few centimeters (in the case of chalk, for example) or many meters deep.
This type of soil does contain water and nutrients for plants but they are often not readily available. Plants which are grown in subsoil tend to be pretty stunted and generally unhealthy.
By adding air, organic material and micro-organic activity, subsoil can be slowly converted into topsoil over a period of time.
Topsoil is the layer of soil that’s been enriched through the ongoing addition of organic material. The resulting humus is assimilated into the soil to make loam.
Loam is soil that is not only rich in organic material but also open and light. It will be created regardless of the basic type of soil if you grow lots of plants and dig in or mulch plenty of organic matter every year.
The deeper the topsoil, the more easily roots can grow and take nutrients on board. It will drain better and retain more water too. Perhaps most importantly, the soil will also be far easier to work.
If you explore a garden that has been cultivated for centuries, the topsoil can be as much as a meter deep. Contrast this with new gardens on uncultivated lands and it will be almost non-existent. In this case it needs to be either made or imported.
Remember: it is never too late to start improving the loam and you will notice extremely beneficial results.
Structure Of Soil
The structure of soil is as crucial as the nutrients in the ground.
You can easily test this for yourself. Grab a handful of loose, dry soil. Squeeze it up tightly in your hand. In the ideal scenario it will hold together in a firm shape but break up again when you drop it. Soil that is light or thin will not hold its shape at all. When it’s dense or sticky, it will not crumble as it falls down.
The best method for improving soil structure is to add organic matter, especially if it’s well-made garden compost. Even chucking in layers of straw or fallen leaves will be a significant help, though.
How To Further Improve Soil Structure
There is little you can do to change the type of soil you have but you can always work to improve it. Organic matter is the key.
Think of the relationship you have with soil as one of mutual benefit. Learn as much as you can about your ground and then extract the very best from it.
One tweak you can make involves having smaller or less vigorous plants. Plants adapt and will make the most out of any given soil even if it means limiting their rate of growth and size.
Explore Your Soil
Soil is generally made up principally of one of the four main geological types:
The precise make-up varies not just from garden to garden but also within the same garden. This is why getting to know your soil intimately is so critical.
Dig it, feel it, smell it…
- Spoon up some soil and place it in a jar of water then shake it around. Within an hour or so it should settle into mini layers. Sand sits at the bottom overlaid with silt. Clay will remain on the top
- Dig a hole 1m deep in various places throughout the garden. Look for the different layers of soil, check out any compaction, examine the depth of your topsoil and also any roots you encounter. Are there any worms? This process alone will further familiarize you with your soil’s structure
- Pour a bucket of water into each of the holes. How long does it take to drain away? If it takes more than an hour, you soil is heavy and slow-draining. If you have fast-draining soil, the water will be gone in ten minutes or less
We will look now at the different types of soil.
Clay soil is the most naturally fertile. Properly treated, you can grow almost anything in clay soil.
Any soil with more than 25% clay particles is termed a clay soil. These particles are absolutely tiny. Sand particles are one thousand times larger.
Clay packs together very tightly. There is very little room between the particles for air, roots or micro-organisms to move.
What this means is that you will need to add a generous dose of organic material in order to open it out. Use a thick mulch in the autumn and spring. Garden compost, horse manure and mushroom compost are all smart choices.
Also, nutrients will not wash through the soil. With a large surface area for plant roots to come into contact with to absorb the goodness, high fertility is almost guaranteed.
One of the drawbacks of clay soil is the need to work it at precisely the right moment. If you don’t do this, it can clump up and become quite unmanageable.
Horticultural grit and sharp sand are both excellent for increasing the size of the particles and opening out the soil structure nicely.
This type of soil drains quickly and is a pleasure to work with.
Chalky soil is very light and has a high lime content. This helps it to break down humus rapidly. Mulch any ground that you need to dig as thickly as possible in the autumn. Dig it in early spring directly before sowing.
Sometimes, chalk will lie above a belt of clay. This leads to the chalk draining quickly but the water then sits on top of the clay.
The main advantage of chalky soil is that it attracts a glut of earthworms.
Chalky soil is extremely alkaline. This should lead you to eliminate any acid-loving plants and to embrace the wide range of plants – including flowering shrubs – which thrive in these conditions. Clematis is absolutely perfect. Any Mediterranean herbs like lavender, rosemary or thyme will get exactly the balance they need with good drainage thrown in.
This type of soil is invariably termed hungry. This refers to the large volumes of added organic matter it cries out for in order to create a great soil structure.
Sandy soil is often light and free-draining. It’s very easy to dig, warms up swiftly and does not waterlog.
The sand particles are relatively big with a small surface area compared to clay. Gravity causes the water to be propelled quickly downwards. It will wet the humus and leave a film of moisture on the grains. Water dissolves nitrogen and other nutrients then carries them down to the water table. We call this leaching. This process is also responsible for washing away the calcium which makes a soil alkaline.
The final type of soil is peat soil.
Wherever you encounter wet ground with the nitrogen and lime washed away you will find this type of soil.
Peat is highly acidic so you should grow plants accordingly. Many will tolerate pHs below 6.5 without any problems.
You can sweeten up a soil like this by adding in some lime.
You should also throw some quicklime or calcium carbonate onto the bare soil one month before sowing or planting. Don’t put on any manure at the same time as it will react badly with the lime.
The more you know about your soil, the better results you will achieve in your garden.
Take your time getting to know precisely what type of make-up is present in your garden. Experiment. Read up on it.
Enjoy the process of working the soil and embrace this as a natural part of the gardening process.