Exogenous application of hormones in plants is a valuable technique for studying and manipulating plant growth, development, and responses to environmental stimuli. The foliar spray method is one of the most common approaches for the exogenous application of hormones in plants due to its ease of use on aerial organs (such as leaves and inflorescences) and the rapid absorption of the treated tissue, facilitating subsequent analyses. Here, we provide a protocol to implement this method in maize. The approach consists of preparing dilutions of the hormones or plant growth regulators (PGRs) of interest, usually in an aqueous solution and at low concentrations, followed by application by foliar spraying using a defined treatment regimen. Users can then evaluate effects by measuring different parameters, such as stem size, flowering time, seed production, or others. The foliar spray method can easily be scaled up and automated in greenhouse and field settings, and can be used to treat plants at all developmental stages.