flower box over clay soil
If I have a flower-box for plants on top of clay using top soil, would they live?
Clay is rich in nutrients but can bake hard in dry weather causing problems for plant roots. Putting a box of soil on top of the clay would be fine if the soil is deep enough for the roots to develop properly. It would be better to break up the clay and dig in sand or grit and then put the soil box on top. That way you get the best of the nutrients in the clay without the risk of the clay forming a solid barrier to roots