A fertilizer composition for application to leaves of a plant includes oxidized glutathione and one or more fertilizer components. A method for cultivating a plant includes applying oxidized glutathione and one or more fertilizer components to leaves of the plant. A fertilizer kit for application to leaves of a plant includes oxidized glutathione and a composition comprising one or more fertilizer components, wherein the glutathione and the composition in the fertilizer kit are separate from each other.