For your hot summer climate I recommend a Rosemary 'Prostratus' that will drape over the wall as you will have fragrance, spring blooms and evergreen foliage. You can also add some hanging succulents such as burrows tale or consider a heat loving vine like the trumpet vine. I do like the look of the Aurbretia but I do not think that plant would survive your summer heat.   When growing the herb Rosemary be sure the site has good drainage and do not over feed or give too much water. Rosemary is easy to propagate from cutting and will root where it touches the soil so you can get many plant cuttings from just one mother plant. Be sure you get the variety mentioned above as some Rosemary will only grow upright into a shrub but for you wall you need the Prostratus variety that will cascade. Keep growing, Marianne Binetti