Sourwood, Oxydendrum arboreum

When I first learned to identify the sourwood tree, Oxydendrum arboreum, I was amazed at how I had not noticed this tree before.  It is found where acid soil exists throughout the southeastern United States, and especially in the mountains of North Georgia and Western North Carolina.  The sourwood tree is also known as Lily-of-the-Valley-tree, Appalacian Lily tree, and Sorrel tree.  It is a medium-sized tree that is most often an understory among larger trees, but it has features that make it easy to identify and enjoy.

The sourwood tree earns its name from the sour taste of its leaves.  This taste is similar to the taste of the wood sorrel plant, and that is why the tree is also referred to as sorrel tree.  Leaves can be safely tasted, and foragers have been known to chew on the leaves to relieve thirst.  However, the leaves are not considered edible as the oxalic acid which gives it a sour taste promotes formation of kidney stones.  Sourwood leaves and flowers appear very similar to those of blueberries, huckleberries, azaleas and rhododendrums, as they are in the same family.  Leaves are elliptical or oblong, pointed at both ends, and edges are finely toothed.  They are feather-veined with a conspicuous midrib.  They are 3 to 8 inches long and 1 ½ to 3 ½ inches wide.  Leaves are attached to twigs by long and slender petioles.  Leaves appear to weep or hang downward from the twigs, and branches droop toward the ground.  As leaves emerge from the buds they are bronze green, and when full grown they are dark green.  In late August the leaves start to turn crimson, purplish red, orange and yellow. Trees along woodland edges with eastern facing slopes will typically have more color because they receive more midday sun. Sourwood trees begin to show their fall colors earlier than most trees, and the colors are beautiful. Fall leaf colors are crimson, purplish red, orange, and yellow.

Sourwood trees bloom later than most trees, from mid June to late July.  The fragrant white flowers are about ¼ inches long and are shaped like a bell or upside down urn.  The bell shape of the flowers is due to the fusion of 5 petals.  The flowers droop downward in clusters appearing much like the flowers of the Lily-of-the-Valley plant, and that is why the tree is sometimes referred to as Lily-of-the-Valley tree.  Trees that get more sun typically have more flowers, and flowers can be so numerous that trees can appear covered in lace.  Bees love nectar from sourwood blooms, and sourwood honey is considered very high quality.  Flowers produce upright 5-valved capsules about 1/3 inches long, holding tiny seeds with two wings.  The dry silver-gray capsules remain on the tree into autumn, providing added ornamental interest after the showy leaves drop.  If you look under a tree in winter you will probably find entire sprays of dried seed capsules that have fallen to the ground in one collective piece.

Sourwood trees often grow more diagonal than straight up, with branches spreading horizontally to drooping.  These branches produce smaller branches that often grow straight up. The appearance of this branching pattern can help in identifying the tree in winter.  Indians liked to use the straight upward growing branches for arrow shafts, because they required little straightening.  Bark on young trees is smooth gray with orangish brown fissures.  As the tree grows the bark becomes thicker, darker gray and more deeply fissured, and develops a blocky, alligator appearance resembling bark on a black gum.  Trees in the Piedmont region typically reach no more than 30 feet tall with the trunk about a foot in diameter, but in the Appalachian mountains they are often over 50 feet tall.  The national champion sourwood found in Amelia County, Virginia is 95 feet tall and about 40 inches in diameter.

The sourwood tree has beautiful flowers, showy seed capsules and colorful autumn leaves, so it is natural that people would want to plant the tree as an ornamental. However, the tree has requirements that make it difficult to grow in most areas that people would like to plant them.  The tree is naturally an understory tree. It prefers 4 to 5 hours of sun per day and does not thrive well in full sun.  The tree requires acid soil and does not like to compete with lawn grass or other ground cover for nutrients.  It does not tolerate drought well. Growth is only about a foot each year, so growing this tree requires patience.  Also, despite staking, this tree is difficult to establish growing straight. The sourwood tree is best planted as an ornamental addition to larger trees in large yards, or in parks. Sourwood trees are most often found along woodland edges or among sparse trees. Being an understory tree among larger trees, it is typically neglected until something unusual catches the eye. The flowers and seed capsules can be very noticeable from June into fall. Fall webworm at the ends of branches may appear in late summer and be very noticeable.  In early fall the leaves become very showy turning crimson, purplish red, orange and yellow.  In winter the branching pattern of the tree is noticeable, compared to surrounding trees. This is a fun tree to identify and enjoy.

Author: David

I grew up near Clayton, AL and have lived over 30 years near Atlanta, GA. My interests include family, church, guitar, gardening, working with kids... and math! Life can be very interesting. My websites: chasingtrees.net mathshortcutblog.wordpress.com View all posts by David