Abstract: A biogenic ice nucleation inhibitor, derivable from a source plant which is normally subjected to freezing stress in its natural habitat, is employed for protecting light frost-sensitive plants against frost injury by inhibiting the ice-nucleating activity of the ice-nucleating bacteria normally present on the plants, and thereby reducing the temperature at which frost injury occurs. The inhibitor is applied to the plants in the form of a solution of a water-soluble denaturable proteinaceous material derivable as a water extract of a source plant component which survives the freezing stress to which the source plant is normally subjected in its natural habitat, such as the seed. The inhibitor is also applicable for reducing the temperature at which ice formation occurs in any other medium containing active ice nucleation initiators, such as, for example, the atmosphere and concrete.

Abstract: A synthetic polymeric ice nucleation inhibitor is employed for protecting light frost-sensitive plants against frost injury by inhibiting the ice-nucleating activity of the ice-nucleating bacteria normally present on the plants, and thereby reducing the temperature at which frost injury occurs. The inhibitor is applied to the plants in the form of a solution of a synthetic polymer having covalently bound to its main backbone chain both pendant hydrophobic groups and pendant hydrophilic groups. The ratio of and average intermolecular spacing between the hydrophobic groups and the hydrophilic groups in the polymer, and the molecular weight of the polymer, are selected so that in combination they provide the polymer with a limited room temperature water solubility within the range of from about 1 .mu.g/ml to about 100 mg/ml.