Planting Kentucky Coffee Beans - a great collaboration to save a rare tree
Kentucky Coffee Tree - Gymnocladus dioica (Brant St. Oakville 2007). The
Kentucky Coffee Tree was
placed in the genus Gymnocladus, meaning naked branch, as it is
both late to leaf out in the spring and early to lose it leaves in the fall. The species
descriptor dioica or two houses refers to the fact that trees have
either male or female flowers.
The leaves which emerge in early June are very large doubly compound leaves (bipinnate). These are followed by clusters of fragrant white flowers (terminal racemes). A member of the legume family, Fabaceae, the Kentucky coffee tree produces dark brown leathery pods that contain dark, hard-coated seeds. While roasted seeds have been used to brew a coffee-like beverage, the leaves, seeds and pulp are poisonous. Thorough roasting for at least 3 hours at 150°C is necessary in order to destroy the hydrocyanic acid that is found in the seed (See USDA Plant Guide http://plants.usda.gov/plantguide/doc/cs_gydi.doc).
The Kentucky Coffee tree is quite rare throughout its range. This tree evolved with large herbivores. Its hard seeds could withstand chewing and digestion and could sprout in fertile animal dung. Given its sparse dispersal and widely spaced male and female trees, its survival now depends on fortuitous conditions. The Town of Oakville is working to provide such conditions.
In the fall of 2007, foresters from the Town of Oakville, collected seed from
various locations. Working in collaboration this the Horticultural Department,
the seeds were stored in a refrigerator at the Town Greenhouse at 2ºC or 36ºF
over the winter. The seeds were carefully labeled to identify the tree source
and the location on the tree from which the seed was gathered.
Bob Baker
of Baker Forestry Services oversaw the stratification process and subsequent
scarification
On April 28th, 2008, volunteers from Oakvillegreen Conservation Association and Oakville Horticultural Society processed and planted the seeds. Seeds were then divided to test germination techniques. The tough shells proved difficult to etch with a standard file and a grinding wheel seemed best suited to processing 300+ seeds. From each seed, a small portion of the coat was removed, just where the short stalk (funiculus) would have attached the seed within the pod. The seeds were moistened and set aside for 48 hours. Another set of seeds were processed in a hot water bath (around 90ºC) and set aside for 48 hours.
On
April 30th, Bob Baker demonstrates seed planting depth (5cm or 2" below top
potting mix). Over 800 seeds were planted in peat pots by a great crew of
volunteers.
May 15 under 10% germination
15
days after planting, a few sprouts are appearing - 67 out of the 740
pots. The scarified/soaked seeds from Mississaga St (Top) are showing the best
germination results at this point. Examination of a couple pots, reveals some
seed rotting is occurring particularly in Hot Water treated seeds from Glen
Allen.
May 20 a little over 20% germination - 168 sprouts. Both scarified and hot water treated seeds from the 161 Mississaga Tree are now germinating (more have germinated from scarified seeds than from hot water). Seeds from Glen Allen tree appear to be rotting (click on thumbnails below) with only 4% germination.
One can hypothesize that these seeds were contaminated with a bacteria or fungus. Perhaps there was an issue with handling or storage issue (frozen) particular to that tree or an issue with the seed itself. It is unlikely to be soil born as all seeds were planted using the same soil mix.
June 05 There are now 223 seedlings, with evidence that a few more are to come. Only 17 are from the Glen Allen Tree (see the thumbnail below on the left). The rest are from the Mississaga Tree. They look well, although there appear to be a few that have been lost due to some mishap (tipped over, watering or wind). There now appears to be little difference from germination technique.
June 11. There are now 234 seedlings with evidence of some health problems. The viable seedlings were regrouped to ease care.
There are 24 from the Glen Allen Tree (20 from hot water treatment - suggesting that the hot water may have had some limited benefit in reducing the impact of the unknown rotting agent. There are 210 seedlings from 161 Mississaga tree with 85 from hot water treatment with more from the scarified treatment, but then more seeds were scarified than treated with hot water. The viable seedlings have been shifted together to improve watering. The peat pots show salt deposits on the outside and are beginning to disintegrate. On the more mature seedlings, roots are emerging from the pots (see fourth thumbnail from left). Several seedlings are showing leaf curl with no visible evidence of insect activity, thus a fungal disease is suspected. Two seedlings have browning leaf tips. Three seedlings have died.
161 Mississaga regrouped
Glen Allen
Roots
Leaf Curl Leaf
Browning
July 2nd. A group of dedicated volunteers transplanted 227 seedlings from peat pots to two gallon containers using triple mix. Only 21 of the 250 Glen Allen seeds made it to this stage. Of these 21, the majority are from hot water treated seeds, which apparently helped partially stem the rot that affected the other seeds. The remaining 206 seedlings are from the 161 Mississaga tree with little difference between scarification and hot water treatment apparent.
