The heat is coming and it's time to make sure everything will survive the temperatures we're about to have here in the metroplex. We're usually five or so degrees hotter than the surrounding country side mostly due to running engines and pavement reflecting heat.
Last year I had good success just making sure there were enough weeds to keep in the moisture. Natives are really good at this and are one reason they have survived here for so long. Most of them are grasses but there are a number of vining ground plants that come along as well. For the most part they won't compete too much with the plants you want since they keep their roots shallow. So not only do they help retain the water in the ground they also don't compete to use it up.
Mulch can help too but it's not really made for the job. Although it does create shade, it wicks the moisture up off of the ground and gives a higher evaporation surface. When the wind picks up they dry out quickly and pull more moisture.
Watering throughout the day in specific areas, not broadcast watering helps too. One of my favorites is ice watering. A block of ice will melt slowly and not only release water but also cool the roots down. It's like placing the glass of iced tea on your chest on a hot day while at the same time sipping it. Which isn't a bad idea to do while refreshing your plants.