Abstract: A plant growing agent contains a blue pigment that contains, as a main ingredient, a compound represented by MFe?Fe(CN).sub.6 ! (M is an alkali metal or an ammonium group, and one Fe is of divalent, while the other Fe is of trivalent), and a substance for changing the cuticular of the surface layer of a plant so as to facilitate permeation of the blue pigment into the interior of the tissue of the plant. In a plant growing method, a thick stock solution is first prepared by adding a surfactant and a solvent into a mixture of the above-described blue pigment and the above-described substance for changing the cuticular of the surface layer of a plant so as to facilitate permeation of the blue pigment into the interior of the tissue of the plant. The thick stock solution is diluted 5-100 times with a solvent, and is sprayed onto a plant to be grown.