Have you ever wondered: ‘what is topsoil and where can I get me some?’ The answer is likely much more complicated than you imagine. Topsoil refers to the upper horizons of the soil profile, in which organic matter has been incorporated through chemical leaching and the ongoing activities of soil fauna and flora.
If you go to a garden center, it’s highly unlikely that what they sell as ‘topsoil’ meets that definition. Usually the so-called topsoil available for purchase is mix of sand and pond muck. Sometimes it is excavated clay that is screened and mixed with sand to give it a workable consistency. The problem with the former (other than the fact that it is not topsoil) is that organic matter will wash through or decompose within a few years, leaving plain old sand. The problem with the latter is that the sand will fill the interstices within the clumps of clay, leaving something akin to concrete. What to do, what to do?
During times of economic boom, it is often possible to purchase actual ‘topsoil’ that has been collected from sites which are being developed for homes, offices, hospital expansions, etc. Given that such economic growth is pretty nil right now, the best you can do is buy compost. If you are working with sandy soil, adding compost will give you something that will act a bit like a good loam. If your parent material is clay, adding compost will increase drainage and boost the activity of soil organisms.
These soil organisms are what turn a heavy unworkable clay into a proper rich topsoil. It is the ‘glue’ that is formed through their activities that causes the clay to develop into aggregates. This is called ‘soil structure,’ something that is lost when the soil is compacted, or that can be badly compromised by unnecessary tillage.
Some people complain about clay, but I sorely wish the parent soil of my garden included some of it. There’s only so much you can do without it. So endeth my rant. If you have insights on this most basic of garden topics, please step forward!