Here in France it would seem that very few people seemed to have seized the concept that topsoil and subsoil are not the same thing!
Almost every time I go to meet clients in a newly constructed house I find I am confronted with the same issue. Where did he topsoil go?
Around Toulouse we only have an average of about 30 cm of the precious stuff, if we’re lucky.
Topsoil is the layer of soil at the surface that has organic life active in it. Organic material and bacteria creating a living support which allows plants to grow. It takes millions of years to form this layer!
Below the layer of topsoil is subsoil which is basically almost inert.Just to simplify enormously
Unfortunately most of the people involved in the construction of a house in my area ( terrassiers, maçons, architects etc) have no idea what topsoil is and so make no effort to preserve or protect this limited finite resource. In so many cases the topsoil is removed to level a platform for the construction of a house to begin but we never seem to find out where it is removed to! What we do know is that its resale value is considerable! There are many cases where the topsoil is just moved aside but then it is buried under a layer of subsoil as the underground garage is excavated. Sometimes the subsoil from an excavation of a pool is spread as a layer over the topsoil ruining it forever in exactly the way that handful of sand would ruin a dish of spaghetti
If you’re thinking of building a house and eventually creating a garden around it my advice would be to make sure that your topsoil is protected, preserved and stocked in mounds no higher than 1m so that the organic activity requiring oxygen can continue within it. Guard it carefully to make sure nobody contaminates it on site. Then when you put it back into position in your garden, hey presto plants grow in it!! I need not add that it makes all the difference……