Editor’s Note: William Cocke is a longtime gardener and native plant enthusiast with an interest in the relationship between gardening and the natural world. For more than 10 years, he wrote a monthly natural history column, “Blue Yonder,” for Blue Ridge Outdoors. He also provided editorial assistance for the regional guide, Piedmont Native Plants: A Guide for Landscapes and Gardens.
On a cold winter day, the first of March 1796, French botanist André Michaux found himself on a bend of the Cumberland River not far from the northwest escarpment of the Cumberland Plateau. He was in Tennessee, exactly three months before it became the 16th state, in present-day Jackson County.
A tree in the forest caught his eye. Perhaps he noticed a vaselike silhouette against the sky, or on closer inspection, he ran his hand across thin, mottled dark gray bark that resembled a beech tree. Later, when he inspected the yellow heartwood, he recognized the tree’s commercial potential as a source for infusing dye.
His journal entry records the moment of discovery and, incidentally, provides a glimpse into an 18th-century plant gatherer’s fieldwork:
“The 2nd remained over in order to pull young shoots of a new Sophera I had remarked in the vicinity of Fleen’s Creek about 12 miles from the Fort [Fort Blount, on the north bank of the Cumberland River near the present town of Gainesboro, Tennessee]. Snow covered the ground and I was unable to get any young shoots but Captain Williams, the young [officer] stationed in the Fort, cut down some trees and I found some good seeds. I also pulled up some roots of those trees to replant them in my garden in Carolina. The same day I had occasion to write to Governor Blount.”
The tree that elicited such prompt correspondence with the governor was the yellowwood (Cladrastis kentukea). Michaux was the first European to encounter this tree and collect it for further study. He most likely never saw a yellowwood in full leaf and in bloom, for the 1796 expedition was his last to North America. He died of a tropical fever in Madagascar in 1802. A few years later, his son, François André, successfully collected and shipped seeds to France, where they may have been planted in the Tuileries gardens in Paris.
A Mysterious Backstory
Yellowwood is the sole Cladrastis species in North America, with the remaining species located in China and Japan. Though endemic to the eastern United States, the trees were uncommon even before European settlers began their assault on the great Eastern hardwood forest. On a map, the tree’s native range looks like a spray of paint across the Southeast and Midwest, from western North Carolina into extreme north Georgia, spanning Tennessee and Kentucky, continuing west to Missouri, Arkansas, and Oklahoma, dipping into north Mississippi, reaching down into Alabama, with a couple of splats in southern Illinois, and one disjunct splotch in Indiana, the northernmost extent of its range.
The relatively small Indiana population is far removed from larger ones in Kentucky, Tennessee, and Missouri. A DNA study conducted by the Hardwood Tree Improvement and Regeneration Center at Purdue University found that the Indiana trees are genetically distinct from the trees in those states, meaning that they are true relicts (a formerly widespread species that persists in an isolated area) rather than trees brought to Indiana by early settlers.
The odd distribution pattern remains a mystery, though we can speculate. The tree is hardy from Zones 4-8 and performs well when planted far outside its native range. It is a legume that does not fix nitrogen, so it favors habitats such as those found in bottomlands or southern Appalachian cove forests. It’s not particular about soil pH. Perhaps its rarity in the wild and scattershot distribution suggests a wider range that was pushed ever south as the result of eons of glaciation, with isolated populations pocketed in islands of favorable habitats—a living archipelago of yellowwoods.
Such scarcity can be bad news for a tree. Fortunately, for the yellowwood, its tendency to fork close to the ground allowed it to escape widespread commercial logging operations. It was used primarily for dye making, first by Native Americans and then by settlers. The wood is strong and heavy, easily worked and polished, which made it desirable for gunstocks and small articles of household furniture.
A Tree for All Seasons
Today, we desire the yellowwood less for utilitarian purposes and more for its nearly unmatched all-season beauty in the landscape. Let’s start with spring. If Michaux had encountered his yellowwood after it broke dormancy, he would have delighted in seeing the pale green growth of the year unfurling from buds encased on zigzag twigs. The new shoots quickly enlarge into pinnately compound leaves that have 7-9 ovate leaflets alternating along the rachis, or primary stem of a compound leaf. The terminal leaflet is larger than the lateral ones. Growth is rapid, resulting in a 10–15-inch compound leaf that turns a lush green by midsummer. By fall, the leaves turn a rich golden-yellow.
Yellowwoods begin to flower after about 10 years, usually in May and June, transforming the tree’s appearance from sturdily attractive to knockout gorgeous. The tiny inflorescences emerge with the leaves along the branch tips to form pendulous, panicled chains of fragrant, white, wisteria-like flowers that can reach lengths of 14 inches. The presence of a mature yellowwood in full bloom, on a warm June day, with perfumed garlands of flowers swaying in the breeze, attended by the gentle drone of thousands of honeybees, is an all-sensory delight that must be experienced to be believed.
There is a pink-flowered variety named ‘Rosea’ — synonym, ‘Perkins Pink’ — that was apparently discovered on the grounds of the Perkins Institute for the Blind in Massachusetts during the 1930’s. It’s unclear whether it is a variety or a hybrid.
Prune or Die
Yellowwoods flower every two to three years. It’s as if the tree can only intermittently sustain such a showstopping production. Fairly slow growing, it achieves a wide crown and, in the open, can reach a height of 30-50 feet, with a similar spread. Trees found in woodlands tend to grow tall, with flattened crowns, their blooms hidden high in the forest canopy. In the landscape, unless you’re working on a capacious, estate-sized canvas, yellowwood is best used as a specimen rather than as a mass planting. While an allée of yellowwoods would have a stunning effect, most of us can content ourselves with one or two.
Nursery grown balled-and-burlapped trees transplant well into fertile, well-drained garden soils. However, pay particular attention to the branch structure. Perhaps the biggest challenge when growing a yellowwood is dealing with its tendency to fork low on the trunk. Proper pruning technique is a must and may hold the key to the tree’s longevity in the garden. An unpruned tree may begin to develop problems after about 30 years, with weak crotches and heavy limbs that are prone to splitting from the trunk. Begin pruning a young sapling to favor a single lead, spacing wide-angled branches along the trunk, favoring strong U-shaped crotches. Yellowwoods are prolific sap-producers, so make sure to prune in late summer or early fall to avoid excess weeping.
Decline and Fall
My wife, Sally, planted a pair of yellowwoods on a southwest-facing slope of our yard in 1995. When I arrived on the scene in 2005, they were already sizable trees, with rounded canopies and cool, deep shade in the heat of summer. True to form, they bloomed intermittently, with consistent mellow gold fall foliage.
Then, in the spring of 2020 we had two hard freezes—the first one in late April. During the second, in early May, temperatures plunged into the 20s for two excruciating nights. This double whammy killed the delicate new growth on our trees twice within a few weeks. The larger tree took a long time to leaf out afterward, while the smaller one seemed to recover.
By the following spring, and as the year progressed, the larger yellowwood started showing signs of severe stress. Its canopy began to thin. Some branches died, while water sprouts developed low on others. The bark split open on the trunk like cracks in old, dry leather. Insects moved into the openings. Shelf fungus appeared. The ground around the tree was littered with dead twigs and small branches.
On January 3, 2022, the heavy, wet snow that destroyed thousands of trees in our area also damaged the smaller yellowwood, perhaps fatally. It took us a few days to notice that the trunk had developed a quarter-inch crack in the trunk just below the first set of limbs. Some of the limbs were themselves cracked and split.
A series of extreme weather events, over the course of two years, were enough to deal death blows to our yellowwoods. We’re not sure of our next steps, but it’s obvious that we may have to take the trees down. I do know that, in the future, I’ll never take a yellowwood for granted.
Looking at them now, on a winter day, in their gray dormancy against a snowy backdrop, they appear almost as if nothing’s amiss. If I try, I can conjure up a June day when the leaves are green, the flowers buzz with life, and the fallen petals carpet the ground like snow. I guess that will have to be enough.
References
Featured Photo by William Cocke
Cullina, William, Native Trees, Shrubs, & Vines: A Guide to Using, Growing, and Propagating North American Woody Plants. (2002Houghton Mifflin Company. Boston, New York)
Dirr, Michael A. Dirr’s Encyclopedia of Trees & Shrubs. (2011,Timber Press. Portland, London)
Sternberg, Guy & Wilson, Jim. Landscaping With Native Trees: The Northeast, Midwest & Southeast Edition. (1995, Chapters Publishing Ltd. Shelbourne, Vermont)
https://hort.ifas.ufl.edu/database/documents/pdf/tree_fact_sheets/clakena.pdf
https://www.indefenseofplants.com/blog/2018/5/28/the-curious-case-of-the-yellowwood-tree
https://www.inwoodlands.org/yellowwood-cladrastis-kentukea/
https://www.ajlambert.com/history/stry_mdm.pdf
http://arnoldia.arboretum.harvard.edu/pdf/articles/1977-37-3-cladrastis-the-yellow-woods.pdf
https://www.ideals.illinois.edu/bitstream/handle/2142/18118/INHS2007_28.pdf?s%20equence=2
https://bernheim.org/learn/trees-plants/bernheim-select-urban-trees/yellowwood/