As you might guess from its common name, river birch (Betula nigra) is best suited to moist sites. It grows naturally along riverbanks and in wet bottomlands. It prefers fertile soil with a pH below 6.5. At a higher pH, iron chlorosis (noted by interveinal leaf yellowing) may develop. River birch is more heat-tolerant than most birches, but it is not drought-tolerant. It requires a lot of moisture to do well.