Kudzu is a climbing, woody or semi-woody, perennial vine capable of reaching heights of 20 - 30 m (66 - 98 ft) in trees, but also scrambles extensively over lower vegetation. Kudzu is sometimes referred to as "the plant that ate the South", a reference to how kudzu's explosive growth has been most prolific in the southeastern United States due to nearly ideal growing conditions. In all, kudzu infests 20,000 to 30,000 square kilometres of land in the United States and costs around $500 million annually in lost cropland and control costs. It cannot tolerate extremely low freezing temperatures that bring the frost line down through its entire root system; however it does require some cold weather (a solid frost or freeze annually).