On 31 Jan, 06:52, Me-G supernanna.cal-
wrote:
My garden has seen a lot of trampling by tradesmen over the past few
years. *Retaining walls were destroyed, weeds, especially docks
flourished and, it seems, all draining material was washed away. *The
garden is like a solid mass of clay.

Those responsible have agreed to "sort" the problem. *

In that, I suspect you were lucky. If it's got puddled, it was pretty
clay-ey to begin with and there is an old maxim in the building trade
'the quality of the given ground is the client's responsibility'

That said there are 3 well established ways for breaking up clay -
increasing the particle size with sand or grit, adding humous, and
chemical treatment. The alternative is to replace the top layer
with imported loam. None of these are successful in the wet, and I
reckon you won't get much done in time for spring flowering plants.

If the building work has been going on for years, just put up with a
few weeks more and let them do the remedial work march/april time as
conditions permit, and then plant up for the summer.

You are likely to still have to do some work on it yourself for
several years, digging in humus, etc.