Water Oak Quercus nigra Hardiness : Zone 6 - 9 The Water Oak is a conical to round tree, growing 50 - 80' high.  Leaves persist late into autumn and winter and are dull bluish green to dark green above and paler beneath.  The juvenile seedling leaves look nothing like the  species, a condition which may persist for 3 - 6 years.  The tree is also more weak wooded than other oaks and will break in wind, snow and ice.  Acorns are 1/2" long and wide.