Four main ecoclimatic factors, viz. temperature, rainfall, light and wind in. subtropical China were investigated. The frost damage caused by low temperature in winter is the only factor restricting Citrus growing. The indices of minimum temperature of light, middle and heavy frost damage for cultivars of different resistance to frost (Citrus unshiu Marc, and C. sinensis Osb.) are discussed. It was found that the indices are quite different both for different types of weather and for different cultivars. Tw...