An improved method for regulating plant growth has been developed. The plant soil medium in which plants are grown is regulated to a pH in the range of about 2 to about 9, and preferably to a range of about 6.8 to 7.2. Then, Actinomyces viscosus strain GA is applied directly to the plant soil medium. The Actinomyces viscosus, GA delivers a natural biological control agent to plants, rather than a synthetic agent, which acts as a growth retardant and a flower initiator.