I have had to demolish a very old very large greenhouse. It was 12m x
2.5m and backed onto a large south-facing wall. Now it has been
removed I am left with the large south-facing wall and the
greenhouse's foundations (tiles floor etc) that look to be there for
good as they are set in concrete. Can anyone recommend how deep a bed
is required to cover these foundations and still support some growth
above. Obviously I'd like to dig the foundations out, but this is not
possible. Would just grassing the area require less depth than having
a large border? How should I deal with the poor drainage?

I am close to gravelling ober the whole area, which would be easy and
cheap, but rather a shame and a waste of the fabulous sun-trap that
the wall provides.

Many thanks for any suggestions

Richad