Catalpa trees make great specimens for large gardens. Trees that ultimately grow to a large size - many native to forests - form an impressive sight in gardens big enough to accommodate them. Where conditions suit, some live to a great age, and may be enjoyed for years to come by future generations. The glossy, dark green leaves on the Western Catalpa speciosa trees are broad at the base, and each has a narrow point. Bell-shaped white flowers, spotted lightly inside, are carried in large heads in summer, followed by slender, pendulous pods. They have vigorous growth and mature size is 70 ft tall by 50 ft wide. They like full sun and do best in zone 4.