This is one of those hot/dry summers that makes you wish that you had chosen garden plants that can really tolerate a good hot and dry summer. The selection of perennials is quite extensive. Most of your shrubs and trees (once they are established) are very drought tolerant. I noticed recently while dining out that the temperatures outside were in the 100s, more exact, 104 degrees and the shrubs were just as happy as could be. It is amazing to me that after so many hot and dry days in a row, that any plant could be happy but yet they are.
Great choices of blooming plants include all colors of achillea, agastache, asters, coreopsis, echinacea, gaillardia, gaura, helianthus, iris, lavendula, liatris poppies, phlox, rudbeckea, salvia, sedum, solidago, viola, zinnias and finally, roses (Knock-Outs are the most popular). Whew, that was a big list! But of course there are many trees and shrubs that are easy during these bad times...such an junipers, arborvitae, euonymus, yews, hemlock, boxwood, holly, privet, cypress, magnolia, yucca and dogwood trees as well as many other trees.
Trees and shrubs, while drought tolerant, do need to be watched closely during the first several weeks and months of planting to make sure that they do not dry out before they get established and well rooted into the ground. Once the first year goes by or if, by chance we get occasional rainstorms, then your "watch-shift" is over. It certainly is possible to over-water any and all of these plants. Just because you are hot and dry does not mean that the plants are hot and dry. Remember that these are drought-tolerant plants. Only water to a depth of 2" to 4" and only once every 5 to 7 days.