Willow Oak Quercus phellos Hardiness : Zone 5 - 9 The Willow Oak grows 40 - 60' high and 30 - 40' wide.  Leaf color is bright green in spring, dark green in summer, changing to yellow, bronze - orange, yellow - brown and russet - red in autumn.  The acorn is solitary or paired and is 1/2" or less long and wide.