Drip watering plants is not recommended in hot summer areas unless the drip line area is covered with a thick layer of mulch. Drip watering causes roots of plants to grow close to the ground surface where they will become baked by the summer sun unless well mulched.
Instead of drip watering, deep soak an area surrounding the plant every one, two, three or four weeks. Use a circular dirt or stone dike to keep water in place. This means letting a hose run for 30 minutes to three hours until the ground is soaked to a depth of at least 1 or 3 feet, depending on the size of the plant. Force an iron or steel rod with a handle into the ground to test the depth that the water has reached.
The frequency of deep watering depends upon the time elapsed since the plant was placed in the ground. Assuming plants are situated in well drained soil, plants in the ground less than one year will need daily watering, until summer rains begin, to become established, then every two or three days until November when watering can be reduced to weekly. If you are in a region with freezing temperatures, taper off watering six weeks before freezing temperatures are expected. Plants in the ground over three years may need deep watering only once or twice a month during the warm season, and less in winter. Allow the soil to dry out between waterings so air can get to the roots.
Watering frequency also varies by species and amount of shade. Some plants need more frequent watering in summer months. For others, part shade can decrease water needs if they are heat tolerant.
See Planting and Watering Trees for information on trees.
Mulch is placed on top of the soil to keep it moist and insulated from temperature extremes of hot and cold. Mulch may be put down anytime. Clear the area of weeds first, then top with organic mulch such as straw, shredded bark or compost, or inorganic mulch like gravel or decomposed granite.
The type of mulch depends on the needs of the plant. Crushed, decomposed granite, or small to medium gravel can be used for desert adapted plants such as some penstemons. Shredded bark, straw, pine needles, leaves, composted mulch and aged compost can be used for plants that prefer rich soils high in organic content. Compost and composted mulch will add long-term acidity to the soil through rain and watering for plants such as vegetables that prefer acidic soils. Some desert plants, however, hate fertilizer and organic compost and need well-drained, alkaline soil low in organic content.
Make the mulch layer no more than 1-2" deep. Keep mulch 6" away from the root crown and trunk of the plant to prevent disease and excess moisture on the bark that invites critters to nibble. Deep mulch allows rodents to build nests and hide.
If the ground is very dry, water the plant deeply before adding mulch.