To make it possible to control the forms of flowering plants by controlling light quality of cultivation light, without using any chemicals such as dwarfing agents, a method of cultivating a flowering plant selected from the group consisting of the genus Petunia, the genus Pelargonium and the genus Euphorbia is proposed, which comprises controlling light quality of cultivation light in the daylight period after a seedling culture stage, in particular, after true-leaf development until blooming or bract formation to thereby control the forms concerning the height of a plant, the length of a branch, the length of a corolla, the length of a flower tube, the number of florets, the dimensions of a flower cluster, the number of bracts or the length of a bract.