In the grand scheme of things, this is a small set of quibbles, but some of what was conveyed in the recent Summer Wrap-Up lecture was, at best, misleading. I’m not an expert but have been in contact with a horticulture expert and have read enough to know that:
The narrative of vascular growth being correlated with autumn is overstated. Vascular growth happens all during the growing season (which, granted, is acknowledged in the stream). But it is not even necessarily dominant in the fall in terms of, for example, added girth.
The blanket statement that dark (fall) rings tend to be thicker than light (spring+summer) growth rings seems to be a gross mischaracterization. See attached photos grabbed from the web. My conclusion from quick googling is that it’s closer to 50-50 or perhaps slightly more girth added in lighter wood (spring+summer growth). Some examples show, in the same tree, certain time periods (or certain areas around the rings themselves) where light growth is thicker and others dark rings are thicker. Sometimes even within the same year but on one side of the tree vs the other.
Wood from dark rings is denser and there may in fact be more vascular cells per unit time produced in the fall compared to earlier. I cannot find definitive information on this.
All metabolic activity during the growing season is important and there for a reason. Various things, all important and timely, happen in the vascular system all season long. What happens in fall is different and no less or more “important” than at other times in the season.
It is more accurate to state that most temperate trees slow down foliar growth in the fall, but that does not translate into minimizing vascular growth in the spring.
I’m really puzzled about why this particular narrative is useful to Mirai. It doesn’t really hold up to scrutiny. It’s like saying that development of liver cells is more important than development of lung cells: no, they both happen for an evolutionary and biological reason.
I think you’re misinterpreting some of Ryan’s points. Ryan noted that he was speaking in broad brush stokes, but the point being not that one growing season was more important than the other but to contextualize what the tree is doing and why we do certain work in the Fall vs the Spring. And I’ll point out that Ryan has a degree in horticulture and has specialized in bonsai trees for nearly 2 decades. But like he said, if you have questions, bring to the Live Q&A.
You bring up some good points and your photos show good examples of dark and light rings in conifers. On one tree dark rings are wider. On the other the light rings are wider. We will agree there is growth in both seasons and it can vary.
I have noticed on my bonsai trees there is growth in spring and in the fall. Not so much in summer. I usually have more wire cut in during the fall season. So I have seen more bark growth in the fall/ winter time period than the spring/ summer period.
There are also differences between species. Some trees grow all summer long. Some go into a summer dormancy. Some have a single growth spurt (spruce) some have a long growth period (JBP), some of them are elongating species (redwood) and grow more steadily. These were general comments and you can apply them, to how you see them, to the trees you are trying to develop.
To me, the take-away is how important the fall period is for the health and development of these little trees that are so stressed by being in these tiny little containers. You are thinking, and that is a good thing. Thanks for your comments.
PS: Don’t cut off too many leaves now if you want a bigger tree next year.
I have been doing Bonsai for 30 years. Trust me when I say “watch your trees for wire cutting into your trees in the fall”. Ignore it at your peril.
Good points, Brian. I took the overall message to be that during the fall vascular growth is more important to us as bonsai practitioners whereas in the spring foliar growth is more important. The fact that there are both dark and light rings does indicate that there’s a tangible difference between the spring and fall growth. I just don’t know that I care aside from it being a good time to heal any damage that occurred as a result of structural work.
The way I like to look at it is a case of energy use (spring) vs energy accumulation (fall).
This would be a good point to bring up though. Probably better suited to Forum Q&A than Live Q&A though.
The cells in spring have wide cavities and only a thin cell wall. The tree needs these cells for good water conduction. Countless of these cells, placed one on top of the other, create a connection between the roots and the crown.
In late summer, the cavities of the newly formed cells become smaller and smaller and the tissue denser. The cells now have considerably thicker walls and are accordingly strong and stiff. Since the cell walls themselves are dark, the wood is also colored. These cells are used for storage and also as a stable framework for the tree. In nature, the tree must be able to carry a great deal of weight and withstand strong tensile forces. As a rule, the annual rings on the sunny side are thicker. The rings in the shade thinner. The thickness of the rings can vary depending on the course of the year (rain, heat, drought, etc.).
Ryan explained the principle that nature forms thousands of variants.
Interesting discussion. It seems like an assumption is being made that vascular tissue is created and then immediately becomes static and does not swell at all after the time of creation; similar to a candle being waxed. I have a feeling this is not how it works. I imagine the vascular tissue swells after it is created. While the light wood is created in the spring I imagine it continues to swell until it hardens off. In fact, now that I think about it, Ryan has been pretty specific about this, saying things like “vascular tissues are being loaded up with sugars and starches in the fall”, rather than vascular tissues are being created in the fall.
I had a similar experience when I first started watching Ryan, in which I heard something that did not make sense. I assumed he was mistaken, however, in continuing to listen to him I realized that what he was trying to communicate had been over my head at the time I first heard it.
Always question your understanding.
It’s probably better to refer to some scientific literature instead of basing your claims on a Google image search. Here’s a general biology test on Primary and Secondary Growth in woody plants.
There is a strong underlying scientific basis for what Ryan is teaching even when he adopts a different vocabulary to make the concepts more accessible to nontechnical audiences.