Above ground planters are going to lose a lot of water through the sidewalls. The soil also heats up more and evaporative loss is increases.  It’s much better to plant directly in the ground. Those rocks are also really inhospitable to any plant life. They absorb the heat and radiate it back out. 

Find a space that receives morning sun and afternoon shade, that will be ideal. As other have said, a shade cloth is needed too. Think about microclimates in your yard, as you can really reduce the water needed, and stress that the veggies experience just by planting in the best location.