Clay is a plus/minus - it's good for dams, not great for directly growing ... unless you can carve out a trough in the clay, put drainage in the lower end, and start packing the trough with evrything that rots, kitchen scraps, hedge cuttings, stable waste, etc.
Do that and you end up with a big clay garden pot that'll grow anything.
Well it requires a lot of work but not impossible, south east of France soil is fairly poor quality (clay and iron) but we can grow nice fruits and vegetables, it would need manure and green fertilizer to feed the soil first, and to rotate culture as well.
We've got a block here in W.Australia that had a massive band of thick clay across it .. after twenty years it's been tamed by cutting long trenches into it when it gets wet enough to slice into with a sharp blade (it's harder than concrete in the summer) and blending those big chunks with dry sparse soil from other parts of the block - midway between the two is a nice mix that holds water but doesn't set like stone when dry.
But yep, that's the game with agriculture, long term steady work to improve conditions, soils, drainage, mulch pits, septic lines, fruit trees, etc.
Do that and you end up with a big clay garden pot that'll grow anything.