Last year I purchased an 8ft acer palmatum 'ukigumo'. At that time I didn't think much about inspecting the root ball. After planting the tree it began severely stressing out. I decided to pull the tree from the ground anticipating it needed to be relocated. What I discovered was the roots were growing in a circular pattern and overall didn't appear very healthy. So with research and a lot of holding my breath I went to root pruning. At the time I wasn't sure that was the right thing to do or not. To get an answer I've done an extensive interview with Dr. Linda Chalker Scott an urban horticulturist at Washington State University to get the answer to that question and many more at my blog. So how many other people have had the root bound tree experience?
Rootbound nursery stock is epidemic here. However, based on what you say here your specimen was most likely showing the results of being in poor overall condition at planting rather than being rootbound. Bound roots on a tree become a problem later, if it starts to girdle itself.
You're right Ron, the overall root conditions were horrible. Beyond the circling many roots were simply dead. This tree was in a nursery size 10gal container and was 8ft with a heavy caliper so it had been there for a while. Thankfully like you hear in my podcast the aggressive root pruning I did helped the tree's overall and long-term health. After about a 1-2 months of stressing the tree settled down as fall approached. I'm very eager to see how it buds out this spring.
Maples get root bound quickly if they are growing well. Anyone who grows JM's in containers for a time will become proficient at root pruning or their trees will suffer. I find that even in large containers JM's will fill the pot within 2 growing seasons after a rigorous root pruning. Smaller, vigorous growers can use re-potting or pruning every year. I agree with Dr. Scott about the resiliency of JM roots. I too have removed, at times, 80% of a plants roots and the tree has always rebounded. My experience with most conifers though is not the same. I'm not very experienced but with pines for example I believe that they are more sensitive to root disturbance and can go for a few growing seasons before pruning or potting up is required. As far as nursery stock and root conditions I'd say that it is UN-usual to get a plant that has been carefully managed in it's container. In my experience even the 'exemplary' sellers commonly ship plants that are either embarrassingly and freshly over potted or desperately pot bound.
I don't know what information Chalker-Scott is using to say pruning roots improves health or vigor. It shouldn't be any different than pruning of tops, which definitely does not increase overall size achieved immediately after pruning or plant health. In fact, root pruning has long been used to stunt top growth in bonsai culture.
Dr. Scot didn't really state that the root pruning increased plant health or stimulated growth. She was stating how root pruning a plant that needs it will help the long term health of the plant. preventing root girdling in the future and allowing the roots to be able to acclimated in to the soil.
I haven't ever opened your link. I was referring to what I've read on her web site. "It’s important to realize that roots respond to pruning in much the same way as the crown: pruning induces new growth. Roots that are pruned at transplant time, especially those that are excessively long or misshapen, will respond by generating new, flexible roots that help them establish in the landscape" http://www.puyallup.wsu.edu/~Linda Chalker-Scott/Horticultural Myths_files/Myths/Fragile roots.pdf "Remember, root pruning stimulates the growth and development of new roots that will enhance tree establishment in the landscape" http://www.puyallup.wsu.edu/~Linda Chalker-Scott/Horticultural Myths_files/Myths/B&B root ball.pdf To me these statements, read in context with the surrounding discussion indicate cutting the roots back stimulates a level of new root production that you wouldn't otherwise get. That is what I wonder about, what seems to be the idea that the plant is invigorated by having its roots cropped. In another column she even describes how cutting tops back does not improve results, yet above she compares root pruning to top pruning as though the similarity in plant response was desirable. Until I find out what perhaps more recent research Chalker-Scott is using for her recommendations on this specific topic I prefer the way Carl Whitcomb (ESTABLISHMENT AND MAINTENANCE OF LANDSCAPE PLANTS, 1987, Lacebark Inc., Stillwater) put it. He said that roots don't like to be disturbed but if it is suspected that a specimen is rootbound it's probably better to open it up and make corrections. You put the transplant through a trial at planting time so it doesn't fail perhaps decades later. There's little about the normal state of woody plants growing in the wild to suggest that they would be adapted to having most of the root system reduced suddenly. It is, however rather common for at least certain kinds to be subject to browsing of the tops. And there is no question that top pruning of cultivated specimens reduces root growth and vice versa.
Ron, Pruning, both above and below ground, activates the plant's emergency survival mechanisms, one of which is to produce new growth. When a plant is damaged in the wild, it must take action to recover and ensure its survivability. Top pruning and root pruning simulate these conditions and actually cause the plant to release chemicals that trigger new buds and roots to form. The good Dr. is correct. Bonsai is not the result of just pruning, its also the effect of limiting the space in which the tree grows, and carefully controlling fertilizer and other environmental factors that force the plant to adapt to its miniature environment.
Stored energy is used to replace growth removed, causing a reduction in the overall quality of the plant's condition. That is in part why severe pruning of a mature tree may cause it to go into an irreversible decline, like the Titanic. Likewise, the fact that our bodies also react to wounds does not establish that they benefit from being wounded. Individual plants do not adapt. That is why the effects produced by bonsai culture are possible. If the specimen was able to adapt to the cultural regime it would not remain changed by it. The plants ingrained limitations and inability to vary from them are being exploited, same as molding a piece of clay into a sculpture.
