We all know that Kentucky has a few weirdness genes in its family tree. There’s that oddball commonwealth thing, the giving directions starting from the old Bacon’s building – and don’t even get me started on “Florence Y’all.” And then there’s the saga of our state tree.
Not content to be like every other state, we apparently can’t be happy with just one. There’s the official state tree, tulip tree (Liriodendron tulipifera) and then we have our state heritage tree – the Kentucky coffee tree (Gymnocladus dioica.) Seems the argument over the two species lasted almost 20 years before a final decision was made in 1994.
But our obligate indecisiveness does not diminish the stellar qualities of this Kentucky native tree.
First the sciencey stuff.
Kentucky coffee tree is a member of the plant family Fabaceae – the pea family. And all of you will certainly remember that members of the family all have bilaterally symmetrical, perfect flowers and their roots form symbiotic relationships with nitrogen fixing bacteria. Wait, don’t go looking up all that gibberish on Wikipedia because the coffee tree is actually one of those exceptions. It doesn’t fix atmospheric nitrogen and its radially symmetrical male and female flowers are born on separate plants – there are boy coffee trees and girl coffee trees.
Coffee tree got its start in western culture when the first European settlers rode their fleet of Yamaha Grizzly 700 XT ATVs through the Cumberland Gap into the lower Ohio Valley. There they found this interesting species that was unknown to western science. They soon found that the large, rock-hard seeds produced by this tree were roasted and steeped by several native cultures into a coffee-like drink. And it appears that it is the look of the “bean” and the steeping in hot water that gave the tree its name … not the flavor of the swill produced!
Also somewhat limiting the culinary appeal of the species is the toxicity of the beans and leaves. They contain relatively high levels of the alkaloid cytisine that can be rendered inactive by thorough roasting.
Typically growing to 60-feet-plus tall with an upright oval shape, coffee tree is famous for its somewhat open growth habit. In fact, the genus name – Gymnocladus – translates to “naked branch” and belies the somewhat coat rack look to young specimens. To be sure, this stately tree has what some might describe as a sculptural branching character.
But filling in the openness between the rather sparsely set branches are amazing leaves. Referred to as doubly compound, each leaf can measure up to 3 feet long but instead of one large leaf blade, the leaf is divided into leaflets and then sub leaflets – each one measuring not much more than 2 inches. The whole effect – the coarse, open branching filled in with lacy blue-green leaves, makes for a unique and fabulous specimen.
Culturally, the coffee tree is amazingly adaptable, making it a great choice for both town and country. Tolerant of both high and low soil pH, drought tolerant (once established) and relatively easy to transplant, it’s a winner on about any planting site. It is highly tolerant of urban air pollution and mostly free from insect and disease problems. The wood is uncommon in furniture and cabinetry work but it is an attractive wood just the same. The wood is also highly rot resistant.
And now for the oh-so-cool coffee tree fact. The species is considered by evolutionary biologists to be what they call an evolutionary anachronism. It seems that the rock-hard seeds contained in thick, leathery pods, are not eaten by anything … at least not by anything currently roaming the Ohio Valley landscape. Turns out that the coffee tree may have outlived those once native quadrupeds like mammoths and mastodons that would have been able to gnaw through the pods and sufficiently nick the hard seed coats, allowing the seed to germinate.
Today, the best way to grow them from seed is to remove them from the pod, file a notch through the epoxy-like seed coat and soak them in water overnight before sowing. Never have a mastodon around when you need one!
For the landscape, coffee tree makes an excellent lawn specimen, street and parking lot tree and park tree. It is useful anywhere that you need a long lived and durable large tree – particularly in difficult planting sites. Male clones are a little cleaner for public spaces since they don’t drop the largish seed pods.
But if you have a pet mammoth, plant a few females and grow some from coffee trees from seed.
Yew Dell Botanical Gardens is at 6220 Old La Grange Road, Crestwood, Kentucky.