With their sweeping branches and glossy, thickly growing leaves, oak trees are a staple of many lawns. Two popular specimens are the live oak (Quercus virginiana) and the water oak (Quercus nigra). These two trees have many similarities: both can grow to about 80 feet, both tolerate wet soil conditions and both are used as street trees. However, they also have a number of differences.
The live oak and water oak grow in different environments. Although the live oak grows in the Southeastern United States and Mexico, the water oak is not suitable for climates farther south than its native Southeastern United States. The water oak’s U.S. Department of Agriculture plant hardiness zone range is between 6 and 9. The live oak needs the warmer climes of USDA zones 8 through 10.
The two oaks have different shapes. Because it is taller than it is wide — growing to 80 feet in height but a maximum 60 feet in width — the water oak grows in a conical form and has a rounded crown at the top. The live oak has a much wider-spreading growth habit. It grows to about 80 feet tall as well but can grow as wide as 100 feet. This broad shape gives the live oak its formidable reputation as a landscape shade tree.
The water oak has a classic oak leaf shape, with leaves 2 to 4 inches long with three lobes at the tips. The live oak has oblong or oval leaves that may be as long as 5 inches. The live oak is also evergreen and keeps its leaves until they grow old and drop off the tree, while the water oak usually loses its leaves in the fall. In warmer climates, however (usually USDA zones 8 and 9), the water oak may act evergreen like the live oak. In that case, leaves will drop only once, when they are old and dead.
Live oak acorns are an elliptical shape about an inch long, with about a third of that length taken up by the acorn caps. Caps are scaly and often remain on the tree after the acorn falls out. Acorns grow in groups of one to five, turn a very dark color when ripe and are valued for attracting wildlife. Water oak acorns are smaller, only about a half inch across. Their caps are woolly rather than scaly.