To keep your plants in top shape and full color give them a monthly feeding of either a dry 5-10-5 or a solution of soluble fertilizer.  A slow-release fertilizer makes the task easier.  You feed only once, at the start of the growing season, and the food is released throughout the summer as needed.  No other food should be used with slow-release fertilizer. 

If it does not rain, water most annuals deeply once a week.  Thoroughly sprinkle the entire bed, not just the plants, or dry soil nearby will pull water away.

Shallow watering only leads to poor root systems that stay near the surface of the soil.  These cause the plants to dry out too quickly.  If the weather is extremely hot or your soil is sandy, you may need to water more often.  However frequently you water, never apply less than one inch of water at a time.

To know when your sprinkler has delivered one inch of water, use a rain gauge, or place an open coffee can halfway between the sprinkler and the farthest point the water reaches.  If you time how long it takes to collect one inch of water in the can, you'll know how long to run the sprinkler the next time.

If possible, water in the morning on days with a sunny forecast, so the foliage will not stay wet too long.