PURPOSE: To enable the delicate control of the growth of a plant, by exposing the plant continuously or intermittently to an ozone atmopshere, thereby controlling the generation and dissipation of ethylene.

CONSTITUTION: A plant, fruit, mushroom, etc. is exposed to an ozone atmosphere by blasting a gas containing several ppm of ozone for 2W3hr, the supply of ozone is interrupted, and the plant, etc. are again exposed to an ozone atmosphere after 6W7 days. Ethylene acting as a plant hormone in the plant can be generated continuously at a rate of 50ppb W several ppm by the intermittent treatment of the plant with the ozone atmosphere. The growing time of the plant can be shortened and the yield and quality can by improved. As an alternative method, the plant is exposed continuously to the ozone atmosphere to effect the decomposition of trace ethylene acting as a growth hormone and an aging hormone with ozone, thereby enabling the maintenance of the freshness and the storage of the plant for a long period.