In the Garden: Sourwood

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By Charles Kidder

Sourwood (Oxydendrum arboreum), a.k.a Sorrel or Lily-of-the-Valley Tree.

Looking for a small- to medium sized tree that flowers in early summer, retains its attractive flower stalks until early fall, and then develops brilliant fall color? The sourwood (Oxydendrum arboreum) fits the bill and can find a place in almost any landscape.

Sometimes known as Sorrel Tree or Lily-of-the-Valley Tree, sourwood is the single member of the Heath family—which includes azaleas and rhododendrons—achieving tree stature in our area. Its small, cream-colored flowers appear on gracefully drooping racemes in early summer, attracting bees and yielding the distinctive sourwood honey. Individual flowers are small, but thousands will cover a tree with a veil of white. Even as the flowers fade, their yellowish stalks and fruits remain ornamental for several weeks. Sourwood leaves are 3” to 8”, elongated and somewhat glossy. A rich green in summer, in fall they turn varying shades of red, purple and yellow, often on the same tree. Even the bark on mature sourwoods is ornamental, a warm brownish gray, divided into deep, blocky furrows.

As someone interested in plant geography, that is, the natural distribution of plants rather than where they can be grown in gardens, I’m always pondering where plants grow. And where they don’t grow. Sourwood is a somewhat puzzling example. Its range stretches from southwest Pennsylvania down to the Florida Panhandle. It is generally found in hilly areas, so is most abundant in the Piedmont and mountains. If you look at range maps of sourwood in Virginia, it grows from the Northern Neck, across the Piedmont through Albemarle County, skips the Shenandoah Valley, but then turns north through most of West Virginia. So, it does grow around here, yet I’ve seen very few in the wild. I do recall seeing one or two on the Blue Ridge Parkway, as well as a conspicuous individual along Miller School Road. (Look for it on the right as you head south, just as you cross over the Interstate. It is possible this particular tree was planted there before I-64 was constructed.) So it appears that at least in this corner of the world, we are right on the edge of sourwood’s range. Why? As near as I can figure, it’s not a matter of temperature, so it could be the soil.

When grown in the open, sourwoods will assume an irregular pyramidal shape, with branches that are held horizontally, to somewhat drooping. You may have to do a bit of pruning at the base to keep a sourwood to a single trunk, but even then you shouldn’t expect a perfectly symmetrical tree. (The Virginia Tech Forestry department refers to it as a tree with “poor form.” Remember: they’re thinking of turning trees into lumber, not as specimens for your garden.) When you see them in the woods, they almost always seem to curve and lean considerably as they age, often at almost 45 degrees. I’ve heard some people say they were leaning toward the light; if so, why are other species nearby growing straight up? And on various occasions I’ve seen one sourwood leaning to the south, while a few feet away another is leaning north, so this just seems to be their innate growth habit.

Sourwoods rarely become really large trees. They might reach thirty or forty feet in height in the wild, with a trunk a foot in diameter, but most garden trees are smaller. In cultivation, they will reach is feet in about as many years. Luckily for us gardeners, they will flower at three to four years of age. They are a bit tricky to transplant, so it’s best to buy a small tree in a container.

Sourwood (Oxydendrum arboreum), a.k.a Sorrel or Lily-of-the-Valley Tree.

Native sourwoods are found either in the forest or out colonizing open fields, so they can take either full sun or shade; flowering and fall color will be better with greater light. If you don’t want to give yours specimen status in the middle of a lawn, planting it at the edge of the woods would be a good solution. Sourwoods occur from well-drained bottom lands to dry hillsides, so they’re not too fussy about moisture once established. Like most members of the Heath family, they do want acid soils.

Sourwoods may not be at every garden center or big box store but are definitely available at area specialty nurseries such as Lazy S’S Farm and are worth seeking out. Both you and the bees will enjoy one!