I have a batch of Valley Oaks (Q. lobata) which I started almost ten years ago on the occasion of my first son’s birth. I had collected the acorns the previous fall in Sacramento from one of the largest Valley oaks I’ve ever seen. In hindsight I can’t say whether selecting the largest tree as the mother tree was the best idea. After all, bonsai is not about the largest tree, but about the most interesting one.
I’ve learned quite a bit about Q. lobata in the last ten years, but I still have a long way to go. Last winter I posted to Bnut about one that I had done a bit of trimming and wiring to over the winter. Well, that tree didn’t have a good spring, it budded out weakly and grew poorly all spring and summer. Was it because I worked on it while it was dormant? Or perhaps it was some other unknown reason? It’s easy to make a guess about what caused the weak growth, but it’s harder to be sure that the cause is accurate.
You can check out the Bnut thread here which contains a few older photos.
I started from the very beginning with the plan that these would all be large trees. Valley oaks have a leaf that will reduce; the minimum size is about 1″ but it will commonly grow to as much as 3-4″. The leaf size is greatly affected by spring sun exposure – essentially the more sun the better as it makes the leaves smaller and more sturdy. While the winter silhouette is the real prize in terms of showing these trees, the spring foliage is also quite nice. Unfortunately, fall foliage is not really a prized characteristic in these oaks, and particularly in San Francisco it doesn’t get cold enough in the fall to make it happen in a nice concerted way.
Repotting in this case was needed because the roots were quite dense in the top half inch of soil and water wasn’t penetrating as easily as it should in good bonsai soil.
When I started these, I planted the acorns directly in the ground. In hindsight, I think I would have started in containers and then planted them out in the ground. Doing so would have allowed more control over the root spread on the trees. In some cases I’ve overcome the initial ground growing problems and in others I have not. The trees took off quickly in my back yard and I did minimal shaping to them initially, both because I didn’t know exactly what I was doing and because I wanted them to be classical upright oaks where the lower trunk is basically straight.
What I know now is that this species will grow well and put on lots of wood and branching while in the ground, but while in a container they will grow much more slowly. That’s actually a great characteristic for a bonsai species because it means that you can control the growth in the container over a very long time. But, it means that if you want to grow from seed that you need to use field growing rather than container growing to get the trunk size that you want.
I repotted three oaks this winter. The one below is the largest because I left it in the ground from when I planted the acorn in March 2005 through January of 2010. At that point I dug it up and put it into a large bonsai container. The trunk is about 4″ across and the tree is currently about 35″ tall.
I’m thinking that a year or two in this container will get the rootball into the shape that I want and then I’ll consider planting it back in the ground for a while.