The relevance of the sustainable management of public green spaces (PGSs) has increased as a result of the global trend of urban growth, especially in arid and semi-arid cities where planners are faced with the challenge of maintaining or increasing plant cover (PC) without increasing water consumption. This study analyzed legal and administrative documents concerning the regulatory framework for PGS in the city of Hermosillo. In addition, the floristic composition and PC of a sample of PGSs (n = 112) was estimated and the impact of this framework was determined using a case study. Our results indicate that the afforestation pattern derived from the current regulatory framework is unsustainable, and it results in insufficient PC in green spaces. On average, exotic species accounted for 62% of the afforestation pattern and PC averaged 27%.