over wintering seedlings

(Question)

i have been very successful in propagating seedlings from pods that i collected from a neighborhood kentucky coffee bean tree but i have been singularly unsuccessful in getting them through the winter. my question is: what have i done incorrectly?

(Answer)

Being able to grow trees from seed that one has collected can be very rewarding. The seeds of the native Kentucky Coffee Tree [Gymnocladus dioicus] pose a challenge as they have a very hard, impermeable seed coat. There are several methods that can be used to scarify (or break through the seed coat) the seeds:

  • use a file, rasp to either make a notch in the seed or file the seed to remove some of the darker seed coating–then soak for 24 hours in water that has been heated to just under the boiling point; seeds should swell up; discard any floating seeds. Coarse sandpaper can be used as well.
  • soak the seeds in concentrated sulfuric acid for two to four hours; rinse the seeds thoroughly and soak in water until the seeds are swollen.

Clearly you have had excellent success in germinating the seeds of the Kentucky coffee tree and growing them to the seedling stage. Your concern is getting them to survive through the winter. (Where do you live?)

When are you germinating and planting the seeds? The best time to do this would be in the early spring; the seedlings would have an entire growing season to become established. If you are doing this in the fall, the seedlings would not be strong enough to survive the winter. [You don’t actually mention what you have done with the seedlings–it’s difficult to determine what you might be doing incorrectly].

How old are the seedlings? Are the seedlings in pots or in the ground? It is recommended that they can be transplanted into the ground after one year.

What type of soil are you using? These trees grow naturally in areas with limestone–even though most potting mixes are neutral pH-wise, perhaps mixing in some dolomite or agricultural lime to your potting mix would make the soil a bit more alkaline.

Do the seedlings have enough moisture before the ground freezes? Kentucky coffee trees require a rich and moist soil–they are typically found on “alluvial soils of river and flood plains and nearby terraces”.

Do you grow them in a protected spot–minimal wind and not in direct sun?  Do you dig the pots into the ground in the fall? You might consider protecting them with a mulch of dry leaves during the winter.

Answering these questions and considering the suggestions will hopefully help you figure out why your Kentucky coffee tree seedlings are not surviving the winter. You’ve mastered the difficult part of getting the seeds to germinate. You are to be commended for growing Kentucky Coffee trees from seed. This tree has many benefits–it tolerates drought and pollution, provides good shade, and is tough and resilient. It is also native to the Carolinian forest and is very desirable as an urban landscape tree.