New build house garden

I was involved with a construction project where half of some underused allotments were redeveloped by a housing association and the remainder were 'refurbished' including provided with sheds and water supplies.

The houses were constructed first, then the allotment plots had the topsoil put back to a depth of (at least) 450mm. Only 300mm was originally planned, but knowing I had an allotment the Landscape Architect checked with me and I suggested a greater depth.

After completion several plots started to suffer badly from waterlogging and it was concluded that after the topsoil had been stripped from the entire site, the exposed clay subsoil had been compacted and baked in the sun forming a hard 'pan' under the topsoil (not imported, but stripped from the original plots).

The problem was resolved by removing the topsoil on the affected plots and breaking up the subsoil with a tractor scarifier (as pic below) the replacing the topsoil.

 

I've had that done in my garden where there were badly compacted areas - under an old Tennis court, for example. Seems to be OK, but I suppose I should have done Half-and-Half in order to be sure that it worked

 

If in doubt, deep plough.