We are often asked "what is topsoil?" well topsoil is quite literally the ‘top soil’, the upper layer of soil, which is usually between two and twelve inches deep, measured from the surface to the first densely packed layer of subsoil. This top layer is where the majority of plants lay the most of their roots, as they are able to absorb nutrients that allow them to grow healthily, due to the high concentration of organic matter and important minerals.
This layer may also contain micro-organisms, worms, insects, spiders, bacteria and fungi. It might sound a bit awful, but these life-forms along with animal faeces and rotting plant matter contribute to the making of high quality topsoil.
Different types of topsoil
There are a few different types of topsoil, and it can vary in texture, content and colour.
The main types are:
- Clay, which is rich in nutrients but doesn’t drain well and can be difficult.
- Sandy, which drains well, but does not hold water so it isn’t much good on it’s own.
- Silty, which is made from quartz and is quite smooth.
Most soils are a combination of these things, but loam, which is the most desirable type of topsoil, and combines the qualities in the right balance of the three types of soil above. A good topsoil will have ideally less than 30% clay, less than 70% silt and less than 70% sand. Achieving the correct balance is essential to thriving plants.
Some topsoil may be more alkaline or acidic depending on the area you live in. This can be corrected or adjusted to suit certain plants and improve their growth.
Find out what topsoil is made of in more detail in our article about How soil is formed.
Some topsoil needs a little attention in order to bear a successful crop. Buying topsoil can be a quick and easy solution, but many gardeners prefer to add certain things to improve it themselves, so they have control of what goes in. This may include manure, mulches or additional minerals to change a soil’s pH balance, depending on what you choose to grow. Gardening enthusiasts tend to prefer organic methods, which add to the topsoil with more nutrition, rather than using chemical treatments. Find out about more soil improving.
Why should I mulch?
Mulches are very popular because they can protect your topsoil from extreme temperatures, while helping to prevent weed regrowth. If you use organic mulch, such as leaf mould or bark/wood chippings, it can improve your topsoil as it breaks down (you can find out more about mulches here).