I strongly recommend getting a rain gauge. You need to know how much water is falling from the sky. A general rule of thumb; if you don’t get AT LEAST ½″ of rain, most soils will only be wet 3 to 4″ deep, leaving the roots dry beneath. If you get several ½ ″ rains in a row the soil moisture will be pushed deeper. Otherwise, you’ll need to irrigate.
For established plants and landscapes, it’s much better to water more deeply and less frequently. You can train your garden to be more water thrifty by doing it this way. In the heat of summer here in arid New Mexico I water once every 7 to 10 days watering long enough that the water goes 8 to 12″ deep into the soil.
For new transplants, even xeric (water thrifty plants) regular watering during the first growing season is essential to grow a strong, deep root system. Don’t water stress new plantings!! BY WATERING DEEPLY AND FREQUENTLY AT THE START OF THE SUMMER HEAT, you’ll save water in the long run as the plants will establish more quickly.
Be sure the plants have a nice, wide, one inch deep saucer-shaped depression around their base to hold water. I also filled the depression with mulch to keep the soil cool and damp. (Yes, I fill the saucer-shaped depression with mulch to help it hold its shape after repeated waterings.) WATER TWICE; fill the saucer to near over flowing, let it percolate into the soil and fill the saucer again.