It’s hard to overstate how important it is for gardeners to understand the soil in their garden.
As indicated in our introduction to garden soil, perhaps the two most important characteristics of soil that you need to understand are soil texture and soil structure.
Here I dig a bit more deeply into the subject of soil texture.
What is soil texture
Soil texture describes how soil feels to the touch and when it is worked with tools.
When we talk about soil texture we are concerned with the mineral particles in the soil and in particular with the relative proportions of clay, silt and sand.
These different mineral soil particles affect soil texture mainly because of their relative differences in size.
Sand particles are generally considered to be between 0.05 and 2.0 mm in diameter, silt particles are 0.002 to 0.05 mm and clay particles are below 0.002mm. Thus, clay particles and hundreds of times smaller than sand particles.
We tend to talk about soil in terms of its weight, whether it is heavy or light. A light soil is one that is easily worked, i.e. easy to dig or fork over. Such a soil will be a sandy or silty soil. A heavy soil is one which is much harder to work. Heavy soils are dominated by clay.
You will also hear soils discussed in terms of whether they are coarse or fine textured. Sandy soils are coarse because they are dominated by the relatively large particles of sand. Soils which are more finely textured are composed of more silt and clay particles.
Can you change soil texture
As gardeners we often talk about improving our soil, for example by adding organic matter or fertilisers.
Such additions can indeed improve the soil structure as well as certain characteristics of the soil such as its fertility or its water holding capacity, but the soil texture itself will not be altered. This is because this kind of improvement does not add to or subtract from the mineral (sand, silt, clay) content of the soil.
It is possible in some cases to change soil texture at a particular site by adding significant quantities of differently textured soil to what is already in place. But this does not really work when it comes to any attempts to increase the sand content of clay soil.
This is because, as indicated, texture is dictated by the relative proportions of the mineral particles. Because clay particles are so many times smaller than sand particles, it is virtually impossible, at least in a garden situation, to add sufficient sand to affect the relative proportions of clay to sand particles. Therefore, the texture remains unaffected.
Soil texture classes
It is useful for soil scientists and even for gardeners to be able to describe soil texture accurately. Therefore various generally accepted soil texture classes have been introduced.
These are the most commonly recognised classes, listed according to whether they fall under the headings of sands, loams or clays and then listed in order of increasing silt and clay content:
Fine sandy loam
sandy clay loam
You might wonder what the difference is between, for example and loamy sand and a sandy loam. The answer is that it is the second word of these descriptions that provides the basic characteristic of the soil. So, in this example a loamy sand is more sand than loam, whereas a sandy loam is more loam than sand.
Why does this matter
Why do you need to know the texture of the soil in garden with any degree of precision?
The honest answer is that you probably don’t need to know down to the finest detail. Whether your soil is a silty loam or sandy clay loam is not going to matter much to you, because those soils are quite similar as they are next to each other in the hierarchy.
However, it will repay you to know whether your soil is sandy, loamy or clayey, because the differences between these broad classes are marked and the soils in the different classes have quite different properties that affect how we need to work with them as gardeners.
I look at each of these different soil types of soils separately on another page.