06/22/2023

Kentucky Coffeetree

The Ohio Chapter ISA’s mission is to advance the practice of responsible tree care while promoting the benefits of trees. This Tree of the Month is commonly known as Kentucky Coffeetree, Gymnocladus dioicus.

Species:  Although native to Ohio, anyone would consider themselves fortunate to discover this uniquely magnificent tree while hiking our woodlands.  The natural range of Kentucky coffeetree extends primarily from southern Michigan and Ohio southwest to Iowa, Kansas, Oklahoma, and Arkansas, and includes parts of Kentucky and Tennessee.  In Ohio, it grows mainly on our west-central limestone soils.

Kentucky coffeetree can reach 75’ in height, is adaptable to a wide range of soils and climates, will survive in dry, compacted, or alkaline soils, has no serious disease or insect problems, and can form colonies from root sprouts.  Ironically, with this adaptability and pest tolerance, it is essentially rare throughout the eastern three-quarters of its native range.  If not for municipal arborists who use its urban tolerance to help create vibrant urban forest canopies, Kentucky coffeetree would remain uncommon and unappreciated.

Leaf:  The uniquely bi-pinnately compound leaves are the largest of any tree in eastern North America.  Each leaf can contain 90 to 100 egg-shaped leaflets alternately attached to a rachilla, which are alternately attached to the central rachis, which in turn attaches alternately to a stout twig.  Leaves are 1 to 2 ½” long and 1 to 2” wide.  When detached, the rachis reveals a large leaf scar that can resemble a heart outline or the shape of Ohio.  Leaves appear late in the spring with a pinkish-bronze color, turning dark bluish-green in summer.  The numerous leaflets give Kentucky coffeetree a fine to medium textured summer appearance.  This characteristic permits more sunlight to reach the ground which allows better growth for lawns and other plants.  The golden yellow fall color is briefly enjoyed.

The genus name, ‘Gymnocladus’ means “naked branch”.  Gymnos is the Greek word for ‘naked’ and klados means ‘branch’.  Because its leaves emerge late and fall early, it is leafless or naked for six months of the year, spawning less common names such as Dead Tree or Stump Tree.  City planners, landscape architects, and others use this attribute if a long season of sun penetration is desired for a particular site.  The leaves, along with its seeds and pulp, are poisonous to livestock, pets, and humans.  Kentucky coffeetree leaves have been used as a fly poison. 

Twig and Buds:  Because Kentucky coffeetree leaves are so large, its twigs are necessarily stout without much taper, giving it a somewhat coarse winter appearance.  According to commercial arborists, Kentucky coffeetree limbs are extremely durable, tolerating moderate amounts of ice and snow without much limb breakage.  Within the hefty greenish-brown twig, which can be heavily lenticular and glaucous (bloomy), is a wide salmon-pink pith.  Like its close relative honeylocust, a terminal bud is lacking, giving new branches a zig-zag pattern.  Dormant lateral buds are nearly sunken in a hairy ring of bark and are superimposed (one above the other) just atop the large leaf scar.

Bark:  Kentucky coffeetree bark is usually an ash-gray color with rough flakey ridges that curl away from the trunk.  It has conspicuous deep furrows running up the trunk in a zig-zag pattern adding to its winter appeal.  According to a USDA Natural Resources Conservation Service publication, some Native American tribes used Kentucky coffeetree bark as part of an appetizer and tonic mixture.

Flowers:  Its species name, dioicus, means “two houses” referring to the fact that Kentucky coffeetree is dioecious or male and female flowers occur on separate trees.  These greenish-white flowers are grouped in panicles and emerge at branch tips after leaves unfurl in late May to early June.  Flowers on female trees are usually more pronounced than their male counterparts.  Since only female trees spawn the large and sometimes bothersome seed pods, the nursery industry has produced a few worthy seedless male cultivars, such as ‘Espresso’, ‘Prairie Titan’, and ‘Stately Manor’, which are becoming more and more prevalent within our urban forests.   

Fruit or Seeds:  By mid-summer, fertilized female flowers transition to yellow-green fruit pods before maturing to a brownish-black color in October.  These dark pods contrast nicely with the bright yellow fall foliage.  The 6 to 10” long conspicuous pods contain six to nine marble-like brown seeds in a fleshy pulp that persist far into the winter.  While in the legume family, Kentucky coffeetree is not a nitrogen “fixer”. 

It is from these seeds that the common name is derived.  Early settlers would roast the seeds, which neutralizes their toxicity, to use as a substitute, albeit a poor one, for coffee.  To be safe for human consumption, seeds must be roasted at 150 degrees for at least three hours.  Native Americans reportedly used roasted seeds for food, as well as using them for games, rattles for music, and jewelry.  Hunting tribes, according to some reports, put large quantities of seeds into rivers to stun fish and make them easier to catch.  Because of leaf and seed toxicity, there is little wildlife usage as a food source.

The size and toxicity of seeds may be the reason for Kentucky coffeetree’s rarity in the wild.  Squirrels and other animals won’t gather seeds because they are toxic, and seeds are too heavy to be carried on air currents, so distribution is mainly accomplished by running water (trees mainly occur within floodplains and river valleys).  The speculation is that before human arrival, the seeds were eaten by now-extinct large animals such as mammoths that tolerated its toxicity, and whose grinding molars and intestinal juices may have aided in scarifying and then dispersing seeds. 

Shape:  Mature trees have a somewhat irregular form.  The bi-pinnately compound leaves present a lacey summer appearance which contrasts dramatically with the coarse winter aspect due to its heavy, thick, zig-zag branches.  Six months of the year, the tree presents a decidedly naked and knobby appearance as if heavily pruned, making it a perfect plant for any graveyard setting. 

Mature Height:  Depending on the site, Kentucky coffeetree can reach a mature height of 60 to 80’ with a 40 to 50’ branch spread.  Trunk diameters of large trees can approach 3’, and trees can live to be about 75 years old.  In urban areas, the cultivar ‘Espresso’ obtains a 50’ height with a 35’ spread.  For this reason, you won’t find ‘Espresso’ on a utility arborist’s list of trees suitable for planting under overhead powerlines.  But, for urban sites without above or below-ground obstructions, this and other coffeetree cultivars should be considered.   

Wood Properties:  Kentucky coffeetree wood is relatively heavy, coarse-grained, light brown to reddish-brown, and rot resistant.  Early settlers used the wood for cabinetry, interior finish, and furniture.  Today, although it is uncommon in the industry, the strong heavy wood is still used for cabinetry, as well as sills, interior finish, fine furniture, bridge timbers, crossties, fence posts (which may last for 50 years), rails, fuel wood, and general construction work. 

Comments:  Though rare throughout its range, whenever found, Native Americans and pioneers used this tree to enhance their daily lives.  Today, because of its adaptability, size, and appearance, Kentucky coffeetree (especially male cultivars), have found a new role in our urban forests.  As an urban-tolerant, pest-free shade tree, Kentucky coffeetree is well suited as a replacement for Emerald Ash Borer-devastated trees and most municipal spaces.  So, if you as a homeowner, municipal arborist, utility arborist, or commercial arborist are privileged to maintain one of these truly magnificent trees and you should consider yourself uniquely fortunate. 

“Although it prefers full sun and rich moist soils, I’ve found Kentucky coffeetree is quite urban-tolerant and adaptable to a wide range of soil textures and pH.  We’ve used the male cultivar ‘Espresso’ in our parks and along our treelawns with great success.  It’s one of my favorite urban trees.”  Jodee Lowe, Grove City Ohio Municipal Arborist

​Tree Selection Tips: The Ohio Chapter ISA recommends working with an ISA Certified Arborist when selecting or caring for any tree in your landscape. To better guide you on the vital plant information for the Kentucky Coffeetree use our friendly users' guide below:

Photograph sources Andrew Todd 2023
Written by Andrew Todd, Former State Urban Forestry Coordinator; reviewed by Mark A. Webber, BCMA, CPH, LTE, MArborA, OCMNT, RCA, TPAQ, TRAQ

Click on the link to learn more about the tree from OSU Extension: https://bygl.osu.edu/index.php/node/2248