PURPOSE: To obtain the agent effective for potted plants and cut flowers, hardly having phytotoxicitv, comprising 2"-O-glycosylisovitexin, a naturally occurring substance having excellent anti-oxidizing activity contained in x'arious green plants, as an active ingredient.

CONSTITUTION: This plant freshness preservative contains 2"-O-glycosylisovitexin of the formula as an active ingredient, obtained by extracting a water-soluble component or an n-hexane-insoluble component of any of various green plants, such as young leaves of barley, with hydrous ethanol having 15-50% water content, optionally with hydrous methanol having 30-60% water content and, in the case of necessity, subjecting to operation such as chromatography or recrystallization. The active ingredient hardly has toxicity (phytotoxicity) to mammals and plants, is safe and will not cause environmental polltution. The application concentration of 2"-O-glycosylisovitexin is 0.001-2ppm, preferably 0.01-1ppm. For example, the preservative is sprayed upon cut flowers, branch materials, leaf materials, potted plants, etc., the cut flowers, etc., are immersed in a solution of the preservative for a fixed time or the preservative is added to a flower vase as the method for treatment.