It's not quite summer yet, but the days are becoming longer and hotter. Heat can be unpleasant for people and for plants. That's sepcially the case when they don't have enough to drink.
The hotter it gets, the faster the water either evaporates from the soil or is consumed and then lost by the plant. Landscapers should make sure gardens receive about one inch of water per week. That means there needs to be at least an inch of rain, an inch of irrigated water, or a combination every week.