Those 2-hole concrete bricks don't hold water very well -- they're worse than terra cotta pots in hot/dry areas.

I've tried planting in them and it doesn't work very well for plants that are heavily dependent on water, like vegetables, even here in the PNW. Some herbs might survive, or some succulents.

A better use for the cinder blocks would be using several to form a bed -- more soil available that would hold more water.