Tuesday, April 12, 2016

Growing Chestnut Trees (Castanea spp.)

A couple of years ago, a member of a forum I frequent offered to send some Chestnut (Castanea spp.) tree seeds to interested parties. He has been breeding Chestnut trees over the last decade and was interested in sharing the results of his work. I expressed interest and soon after a small box arrived, packed with seeds from a few different sources. The box was far larger and held far more seeds than I expected the individual was going to send me.

The seeds were collected from a range of different Chestnut trees:
  • Chinese seedling (C. mollissima)
  • Miller's Hope (C. mollissima)
  • Szego (seedling of Linden; mostly C. mollissima/C. crenata)
  • Gillet (seedling from Colossal; C. sativa/C. crenata)
  • Kaibutsu (seedling from Colossal; C. sativa/C. crenata)
  • Silverleaf (C. sativa/C. crenata)
  • Double Sweet
  • Patterson
Most of them have a mixed ancestry, but all have been selected for high production of large edible nuts. From a long-term view, growing these varieties is entirely about the ongoing domestication of chestnuts as a food source, i.e., improving food security through increasing the diversity of our food plants.

American chestnut range vs. me.
Growing these chestnuts has nothing to do with resurrecting the American chestnut (C. dentata), which is something I consider a very important goal. The American chestnut, in the pre-blight era, dominated the Eastern Woodlands and provided food for a thriving ecosystem (and economy) that has been only a shadow of its former self. Go over to www.acf.org to read more about what they're doing to restore this tree to the dominant role it used to have. Because I live well outside the native range for the American chestnut, I'm not worried about interfering with the their restoration by growing closely related trees that can cross successfully with the American chestnut.

From a short-term view, I'm interested in growing chestnuts simply because I want to grow a new food source. I like having a hand in producing the food I eat and I'm interested in the process of domesticating plants to be better foodstuffs for the future. There really is nothing like planting a tree, that will probably outlive me, for having a future perspective.

When I received the package of chestnut seeds, I had just moved into a new house and didn't have the resources on hand to build the rodent-proof growing area I would need to keep baby Chestnut trees alive. They rely on the nutrients found in the seed for the first year, which is a long time to be exposed to hungry squirrels that like to pull up newly-sprouted nut trees to get at the buried nut. (I learned this when one pulled up a baby Black Walnut tree I was tending, ate the previously-buried nut, then left the uprooted seedling beside its pot.) I had read that Chestnut tree seeds could stay viable for a few years if kept chilled, so I planted a handful of the seeds and kept the others in the fridge. My idea was that by next spring I'd be able to build them some proper protection.

1. Radicle extending.
One of the first batch of seeds germinated and started growing. After it was a few inches tall, the growth point died. A few new branches formed below that point, but their growth points soon died. This pattern repeated a few times before the whole plant died. It had never produced a single leaf, but had branched several times while trying to.

2. Hypocotyl beginning to extend.
I spent some time thinking about what went wrong with that seedling. On the idea that it was getting too much water and developed a fungal infection of some sort, I decided to build a potting system that would allow the seedlings to drain much better. I built a set of primitive air-pruning pots and a raised wire-mesh platform so they could drain. In addition to the better drainage, these pots should help encourage the development of a healthier root system (so the seedling will better survive transplant later in the season).

3. New leaves.
Of this second batch of seeds, only one (a seed from the variety "Kaibutsu") has woken up so far. It is growing happily and is just opening its second set of leaves. The remainder of the seeds seem to have either succumbed to a mold, or are still waiting to wake up. There are reports of chestnut seeds derived from hybrid origin (as most of these are) having reduced germination, but I would need to test a similar batch of seeds as a control. Without that control, I'm left with hoping more decide to germinate, that the elongated winter they experienced didn't kill off the remaining seeds.

4. LED lighting.
When this seedling started waking up, I put it near the front door where I could keep a close watch on it to make sure it didn't dry out. After it grew a couple inches, the drive to find light became the stronger factor guiding its growth and it began tilting towards the nearby window. To help keep the seedling from becoming permanently crooked, I built a rack that holds an LED floodlight directly over it. The base of the structure is a platform extending forward underneath the tray holding the plants, so it has very little risk of falling over. This setup should keep the seedling growing straight until it is time for it to go outside.

5. New lighting and further growth.
After a few more leaves had grown, it became apparent the lighting setup I built was too bright for the seedling. Leaves closer to the light were looking sunburned, while those further away were colored lightly brownish from photo-protective pigments. I think the new fixture produces more light overall, but it is spread over a larger area and so the peak intensity is lower. (This new fixture can also provide light for other plants, like those carrots.)

6. Roots.
The home-made air-pruning pot seems to be doing its job. There are little roots poking out all over the bottom of the container. The roots start out whitish, but then turn a dark brown as the tip dies and dries out. At some point soon, I'll have to transplant the seedling to a larger air-pruning pot. This will allow it to become larger/stronger as well as giving us the time to figure out where it should go into the ground and how to protect it from deer and other hazards. I might be able to make such a planter the same way I made this one, but I suspect I'll have to go with a bit more robust commercial offering.