With its geographic range encompassing almost the eastern half of  the United States, river birch grows throughout a wide range of  climate. It is most abundant in the hot, humid Southeast where  the frost-free season averages from 210 to 270 days and annual  rainfall averages about 1270 mm (50 in). At the northern extreme  of its range in Minnesota and Wisconsin, annual precipitation  averages less than 760 mm (30 in) and the frost-free season is  150 days or less (8).