Does anyone know anything about gardening?

The answer to that question is a simple 'no'. The answer to a permeable base for shingle is crushed concrete with a layer of sharp sand on top. The answer to planting between slabs is concrete and a layer of mortar under each slab and soil in between.

Any area of shingle will inevitably grow all the things you don't want. Leaves will decompose on it, fine soil will blow into it, it will soon become a 'wildflower' bed.