Kentucky Coffee-tree (Gymnocladus dioicus)

Coffeetree, Kentucky Coffeetree, Kentucky Coffee Tree

If you decide to start growing a Kentucky coffeetree in your garden, it will definitely make a one-of-a-kind statement. The tall tree offers large leaves with unusual coloration and large, woody, decorative pods. That said, if you want to plant Kentucky coffeetree in landscapes around your home, you’ll need to know something about the tree and its care. Read on for Kentucky coffeetree information.

I. Appearance and Characteristics 

The Kentucky coffee tree (Gymnocladus dioicus), also known as American coffee berry, Kentucky mahogany, nicker tree, and stump tree, is a tree in the subfamily Caesalpinioideae of the legume family Fabaceae, native to the Midwest, Upper South, Appalachia, and small pockets of New York in the United States and Ontario in Canada. The seed may be roasted and used as a substitute for coffee beans; however, unroasted pods and seeds are toxic. The wood from the tree is used by cabinet makers and carpenters. It is also planted as a street tree.

From 1976 to 1994, the Kentucky coffeetree was the state tree of Kentucky, after which the tulip poplar was returned to that designation.

The tree varies from 18 to 21 meters (60–70 feet) high with a spread of 12–15 meters (40–50 feet) and a trunk up to one meter (3 feet) in diameter. The tree grows at a medium rate with height increases of anywhere from 12″ to 24″ per year. A 10-year-old sapling will stand about 4 meters (13 feet) tall. It usually separates 3 to 4½ meters (10–15 feet) from the ground into three or four divisions which spread slightly and form a narrow pyramidal head; or when crowded by other trees, sending up one tall central branchless shaft to the height of 15–21 m (50–70 ft). Branches are stout, pithy, and blunt; roots are fibrous.

The Kentucky coffeetree is a moderately fast-growing tree, and male trees are often grown in parks and along city streets for ornamental purposes. The tree is typically fairly short-lived, healthy trees living from 100 to 150 years. The Kentucky coffeetree sheds its leaves early during the fall and appears bare for up to 6 months. The naked appearance of the tree is reflected through the Kentucky coffeetree’s Greek genus name, which means “naked branch”. Like the Sumac, branches are absent of fine spray; smaller branches are thick and lumpish. Because of the absence of smaller branches and its later leafing, the French in Canada named it Chicot, “stubby”. The expanding leaves are conspicuous because of the varied colors of the leaflets; the youngest are bright pink, while those which are older vary from green to bronze.

The bark is ash-gray and scaly, flaking similarly to black cherry, but more so. The trees are dioecious, and the fruit is a hard-shelled bean in heavy, woody, thick-walled pods filled with sweet, thick, gooey pulp. Pod length ranges from 5 to 10 inches (130 to 250 mm); unfertilized female trees may bear miniature seedless pods. The beans are commonly thought to contain the toxin cytisine, although this has yet to be confirmed in a study.

  • Bark: Tan or dark gray, deeply fissured, surface scaly, often with prominent narrow ridges. Branchlets at first coated with short reddish down.
  • Wood: Light brown; heavy, strong, coarse-grained; durable in contact with the ground, takes a fine polish. Specific gravity, 0.6934; weight of cubic foot, 43.21 lb (19.60 kg).
  • Winter buds: Minute, depressed in downy cavities of the stem, two in the axil of each leaf, the smaller sterile. Bud scales two, ovate, coated with brown tomentum and growing with the shoot, become orange green, hairy and about one inch long, before they fall.
  • Leaves: Alternate, bipinnately compound, ten to fourteen pinnate, lowest pinnae reduced to leaflets, the other seven to thirteen foliate. One to three feet long, eighteen to twenty-four inches broad, by the greater development of the upper pairs of pinnae. Leaf stalks and stalks of pinnae, are terete, enlarged at base, smooth when mature, pale green, often purple on the upper side. Leaflets ovate, two to two and one-half inches long, wedge-shaped or irregularly rounded at base, with wavy margin, acute apex. They come out of the bud bright pink, but soon become bronze green, smooth and shining above. When full grown are dark yellow green above, pale green beneath. In autumn turn a bright clear yellow. Stipules leaf-like, lanceolate, serrate, deciduous.
  • Winter twigs are very stout and dark reddish brown to green brown in color; the pith is very thick and salmon pink to brown in color. The terminal bud is absent, and the lateral buds are small, bronze in color, and appear to be partially sunken beneath the bark of the twig. The leaf scars are very large, heart shaped with 3 to 5 conspicuous bundle scars. The flowers are dioecious (male and female flowers on separate plants). The female flowers are 8 to 12 inches long, greenish white in color, appear in early summer, and are quite fragrant. The male flowers are about half the size of the female flowers.
  • Flowers: June. Dioecious by abortion, terminal, greenish white. Staminate flowers in a short raceme-like corymb three to four inches (75–100 mm) long, pistillate flowers in a raceme ten to twelve inches (250–300 mm) long.
  • Calyx: Tubular, hairy, ten-ribbed, five-lobed; lobes valvate in bud, acute, nearly equal.
  • Corolla: Petals five, oblong, hairy, spreading or reflexed, imbricate in bud.
  • Stamens: Ten, five long and five short, free, included; filaments thread-like; anthers orange colored, introrse; in the pistillate flower small and sterile.
  • Pistil: Ovary superior, sessile, hairy, contracted into a short style, with two stigmatic lobes; ovules in two rows.
  • Fruit: Legume, six to ten inches (150–250 mm) long, one and one-half to two inches wide, somewhat curved, with thickened margins, dark reddish brown with slight glaucous bloom, crowned with remnant of the styles. Stalks an inch or two long. Seeds six to nine, surrounded by a thick layer of dark, sweet pulp.
  • Rooting Habit, “Tap Root in proportion like a carrot”. A seedling tree grows many times in root length to its growth upward in height. The Kentucky coffee tree is not commonly offered in the nursery trade because the taproot makes the tree somewhat difficult to transplant. Being in the Legume family the roots fix nitrogen in the soil.
  • Soil: Prefers rich, moist soils in floodplains, terraces, ravines, coves, and lower slopes.

Caution should be used when consuming, as unroasted or only partially roasted beans and pods are considered poisonous and are reputed to contain the alkaloid cytisine. The pods, preserved like those of the tamarind, can be eaten and are slightly aperient (laxative). Many sources claim that roasting the seeds for a certain length of time can reduce or eliminate the cytisine thought to be in them, but this is not based on scientific evidence. There are however, many anecdotal accounts of people drinking a coffee-like drink made from the seeds without suffering any adverse health effects, although most reported the taste to be unpleasant.

The plant is toxic to some animals and intoxicates dogs. “Kentucky Coffee Tree intoxication in a dog”

II. How to Grow and Care

Sunlight

The Kentucky coffee tree does best with at least six to eight hours of direct sunlight. The tree will tolerate a small bit of shade.

Temperature and Humidity

Kentucky coffee tree isn’t too fussy about temperature or humidity and is very winter-hardy. It’s not likely to do well in growing zones higher than 8. It struggles in hot, dry climates.

Watering

In times of extended drought, this tree will benefit from some additional watering at its base, about every seven to 10 days. But otherwise, it’s very drought-tolerant and should not require extra water.

Soil

Adaptable to a wide range of soil conditions, this tree manages well in clay but grows a bit better in sandy loam. It isn’t bothered by too much acidity or alkalinity. Being drought-tolerant, it’s also fine in dry spots. Too much wet soil may affect the roots over time, so planting too near a swamp or marshy spot is not a good idea.

Fertilizing

Fertilize the Kentucky coffee tree with fertilizing products that promote woody, strong growth rather than excessive foliage growth. Avoid fertilizing with nitrogen products, since the tree is a nitrogen fixer. (It even works to supply neighboring plants with nitrogen.)

Pruning

The best time for pruning the Kentucky coffee tree is late winter or early spring after the worst cold temperatures are no longer a danger. Its slow growth habit means that young trees won’t need any pruning in the first few years unless the branches become damaged. However, if overly long (thereby weaker) branches develop, these should be pruned when young to promote a stronger structure.

Propagation

Most growers of the Kentucky coffee tree prefer the easier method of propagating this plant by seed. It’s easy to grow a Kentucky coffee tree from seed if you can harvest the pods and release the seeds. Harvest them after the pods have turned brown in late winter to early spring. For successful germination, seeds need to be scarified (but not stratified) to remove the layers of protective coatings. Take these steps:

  • Peel the large seeds out of the pods and remove the protective sticky, jelly-like outer coating.
  • Scarify the seed coat by removing the extra protective brown-black waxy coating with a small file. Keep filing until you can see the true seed, which is more yellowish.
  • Soak the seeds in boiling water (hot is okay) and let the water get to room temperature when soaking for 24 hours. Peel off the waxy coating after seeds soak.
  • Put the seeds an inch or two down into a small pot of potting soil like you would any other seed.
  • Keep in a warm, humid, indirectly lit space, such as a greenhouse.
  • In a few months, the seedling should reach about 6 inches tall with sets of true leaves. Transfer the tree outdoors in the spring when the soil is consistently warm. (You can wait up until three seasons before planting the tree outdoors if you desire.)

Pests and Diseases

This tree has no real disease or insect problems to worry about. There are only a few issues that may be of concern.

Leaf Litter

“Leaf litter” from both male and female trees can be a problem as the leaves are very large and most of them come off the branches in the early fall. The fallen seed pods from female trees, beginning in the spring, can also create a bit of a mess. This makes the tree a better candidate for parks or other open areas, such as a very large backyard, rather than as a street tree.

Contorted Branches

After the leaves fall, the tree’s large, twigless, and completely naked branches will have a contorted zig-zag pattern. This silhouette gives this tree a bold fall and winter appearance perfect for a “haunted Halloween” setting that some gardeners may or may not appreciate.

Yellowing Leaves

This tree does not like to be overwatered, and as a result, it may show yellowing leaves that wilt and drop off too early. The tree usually tolerates occasional flooding conditions.

No Leaves

Kentucky coffee trees are one of the last trees to leaf out in the spring and the earliest to drop leaves in the fall. The trees are leafless most of the year, so it is not unusual to have bare branches from fall through much of the spring.

III. Uses and Benefits 

  • Food

The beans of the tree were eaten, after roasting, in the Meskwaki (Fox), Ho-Chunk (Winnebago) and Pawnee Native American cultures.

The Meskwaki also drank the roasted ground seeds in a hot beverage similar to coffee. The common name “coffeetree” derives from this latter use of the roasted seeds, which was imitated by settlers because it seemed a substitute for coffee, especially in times of poverty, similar to chicory.

In addition to use as a food, the seeds of Kentucky coffeetree were used by Native Americans for ceremonial and recreational purposes. Seeds were used as dice in games of chance that were common in eastern tribes. It is likely that indigenous community members carved patterns on coffee tree seeds used in ceremonial dice games, which also served to scarify the seeds and prepare them for germination. The seeds were also used in jewelry. The importance of the Kentucky coffeetree to Native Americans undoubtedly contributed to its dispersal.

The roasted seeds can be eaten like sweet chestnuts. Usefully, the fruits can be collected and picked up from the tree or ground at any time during fall, winter, and spring.

  • Culture

Gymnocladus dioicus is used as a street tree as far north as Montréal, Québec. It resists harsh winters and de-icing salts.

  • Woodworking

The wood is used both by cabinet makers and carpenters. It has very little sapwood.

Kentucky Coffee-tree (Gymnocladus dioicus) Details

Common name Coffeetree, Kentucky Coffeetree, Kentucky Coffee Tree
Botanical name Gymnocladus dioicus
Plant type Edible
Hardiness zone 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b
Growth rate Slow
Harvest time Fall
Height 60 ft. 0 in. - 80 ft. 0 in.
Width 60 ft. 0 in. - 80 ft. 0 in.
Sunlight Full sun (6 or more hours of direct sunlight a day)
Soil condition Clay
Flower color Green
Leaf color Blue