Author Topic: How is Root Pruning Possible?  (Read 12307 times)

0soyoung

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How is Root Pruning Possible?
« on: January 16, 2013, 12:27 PM »
We all know that we can root prune in the spring (when buds swell). What is it about spring that makes it possible to rip all the hair roots off and have no (lasting) deleterious effects? I would like to understand why.

I've also noticed that it seems to be possible to root prune Japanese maples after bud break, to about the point of hardened leaves and still not have any serious trouble. But shortly thereafter, messing with the roots is pretty much guaranteed to be fatal to the tree. It seems to make sense that maples (and possibly all deciduous trees) have enough stored water, carbohydrates, and phytohormones to not need roots in spring until sometime after the leaves are out?
 
On the other hand, there are conifers, mugo pines in particular, that seem to best be root pruned in August/September (northern hemisphere) instead of spring. Spring is okay, just Aug/Sep makes for stronger mugos and appears to contradict the 'all needs are in store' idea (above). Why would it be that late summer is also a good time to 'rip your trees roots off'?
 

geoffhobson

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Re: How is Root Pruning Possible?
« Reply #1 on: January 16, 2013, 01:54 PM »
Root pruning does not involve ripping hair roots.Roots are pruned and usually taking about a third of the root ball I take this from each side and from underneath the root ball, making a slight concave on the underside. This allows the tree to grow further.
The reason for spring re potting which includes root pruning of course, is that the trees are coming into growth for the year and it is less stressful on the tree.
Geoff
 

Dan W.

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Re: How is Root Pruning Possible?
« Reply #2 on: January 16, 2013, 03:19 PM »
I believe one reason late summer/early fall works for many... if not all conifers, is because they transition into a root growth phase this time of year. So, similar to spring there is a new push of roots. This is my understanding, someone pleas corect me if I'm wrong.  :)
 

pwk5017

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Re: How is Root Pruning Possible?
« Reply #3 on: January 16, 2013, 09:05 PM »
I think the main reason for why repotting is most successful in the spring is the plant is not respirating--and therefore not transpiring water-- nearly as much as say, july. If the tree is not losing as much water through its leaves(for deciduous trees, not at all because it doesnt have leaves yet) then the roots dont have to supply as much water.  Cooler temps, humidity etc. help with this process during the transition from winter to spring.
 

0soyoung

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Re: How is Root Pruning Possible?
« Reply #4 on: January 16, 2013, 11:51 PM »
Thanks for your thoughts thus far, everybody.

Geoff,
I should have been more careful in the way I said things. When I referred to ‘hair roots’ I meant the extensions of single epidermal cells behind the growing root tip – these are the primary adsorption surface of roots. I’m of the mind that these are inherently destroyed when removing the soil. I too often refer to fine fibrous roots as ‘hair roots’ as you assumed I meant. Nevertheless, I think that when we root prune, we cut off the root tips but they are regenerated from the exposed root cambium.

Pwk5017,
Your point about transpiration is a good one. The sudden sensitivity of JMs after leaf hardening that I noted could be exactly that transpiration exceeds supply. This should cause the leaf’s stomata to close to save water, but … etc., etc., and down the drain. This much makes sense to me.

Dan,
Another good idea: spring repot is before a root growth period; late summer / early fall is before another phase of root growth. In other words, there is a period of very little root growth in between! When repotting in spring, we are root pruning in advance of a surge in root growth that lags behind bud break. Messing with the roots at the later stages of this first phase is deadly because there is little or no capacity to replace them at that time. So, then there is a pause and somewhere around September (depending on specie and local conditions, I would suppose) we again are at a point just before another surge of root growth and that is why it again is safe to root prune. Hmmm …

BTW, when I was oh so young I had no patience and no interest in horticulture. Now that I’m not so young, I find trees almost endlessly fascinating. It just stuns me how my wrong my (lifelong) beliefs about how trees were. Trees don’t just wake up in the spring, grow, and go back to sleep in the fall. IMHO, bonsai is manipulating the natural processes of trees to create art. I have the best intentions of getting to the art part!

Thanks again.
 

geoffhobson

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Re: How is Root Pruning Possible?
« Reply #5 on: January 17, 2013, 05:58 AM »
Points taken. However, I think the species is also critical. If you re pot a Larch after the buds have burst then you could well lose the tree. I have had it happen to me, also Mugo Pines are very sensitive when it comes to re potting, and I do them in the late summer rather than late spring as again I have lost two when done then. They also do not like pruning done in the same year as re potting. I would never re pot a deciduous species after bud break as again it puts too much stress on the tree, I have seen members of my local club re pot in most months, but I will not take that risk. Re potting does of course include root pruning.
What we need to do is cause as little stress to the tree as possible, so doing it at the optimum time is crucial, I am sure you agree. Where you are in the world will also have an effect of timing,
Geoff.
 
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0soyoung

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Re: How is Root Pruning Possible?
« Reply #6 on: January 17, 2013, 02:21 PM »
I agree Geoff.

All those things are likely important factors. It is just that I would like to understand a bit more about why. Five years ago I was petrified to even expose a root, just because I was ignorant and sold on the mythology I would kill any plant/tree were I to ever mess with its roots. I planted trees and gardened for many years, but was always careful to 'slip pot' them, in effect. Now I know better (just not enough). My curiousity has been fueled by the peculiar circumstances that my trees/plants survived or died over the last few years. It just indicates it isn't as simple as my present 'model' of how trees work. Life goes on and I undoubtedly will continue to kill a few trees whether I ever answer this question to my satisfaction or not.

Thanks for your help
 

scereghino

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Re: How is Root Pruning Possible?
« Reply #7 on: January 11, 2017, 01:21 AM »
If there is curiosity, grow for a season in a glass bowl/pot. cover the edges so the suns rays do not affect the roots, and observe the changes that occur.
 

mndblwn

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Re: How is Root Pruning Possible?
« Reply #8 on: January 15, 2017, 09:30 AM »
From what I understand you root prune deciduous trees in spring after bud swell because the roots have transferred all stored energy up the trunk and into the new buds. At this point the roots become basically dormant so you can mess with them without stressing the tree. After the buds break and the leaves open they collect energy from the sun and then start to return energy to the roots. For a more detailed explanation you can look up "sap flow in trees". A lot of great articles, though not bonsai specific.


Sent from my iPhone using Tapatalk
 

akeppler

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Re: How is Root Pruning Possible?
« Reply #9 on: January 23, 2017, 11:55 PM »
It seems that many "old world trees" seem to take to repotting in the summer or most anytime really while "new world trees", (after the last Ice Age) seem to like spring only?

Any thoughts.
 

0soyoung

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Re: How is Root Pruning Possible?
« Reply #10 on: January 27, 2017, 12:22 AM »
If there is curiosity, grow for a season in a glass bowl/pot. cover the edges so the suns rays do not affect the roots, and observe the changes that occur.
I did give this a try. I potted some trees in clear plastic orchid pots and made grids that I glued to them, intending to count root crossings of grid lines as a measure. I did this with 8 Dougleas firs, 8 lodgepole pines, 4 zelkova serratas, 4 Eastern redbuds, and 4 cork oaks. I diligently counted root crossings of grid lines every two weeks. I even attempted recounting as many as three times every time I did counts, in order to asses my repeatability with counting.

My personal issues were overwhelming. I had huge problems with repeatability. I had intended to just count new white roots, but I could not consistently decide if this was the extent of 'white' or if it was 'over there'. Unfortunately roots don't abruptly change from white to brown. Then, lighting conditions when I made the counts also had an influence. Sometimes I could see darkish roots on bright sunny days that I couldn't/didn't see on overcast ones. In brief, I came to appreciate why academic researchers use cameras and digital image analyzers to accomplish this.

I could have given this another try last year, but frankly, I've lost interest. I've found a number of scholarly papers that detail there being a strong surge in root growth in the spring. After the summer solstice, roots again grow, but more steadily.

So, currently I think there is a surge in root growth in advance of the rapid growth above ground - roots powered up to support the impending top-side growth. Hence, roots will recover quickly from pruning damage (I've certainly overdone spring root pruning and either killed the tree or spent most of the season nursing it along). Just after the summer solstice, the rate of bole thickening of all species I tested peaks. I believe that this means auxin and photosynthates are now available so that roots are able to recover from pruning. As far as my experiment material is concerned, I continue to repot half of each in spring and half in July/Aug and can see no difference in the two groups.

Otherwise, I continue to repot my maples and other deciduous species (angiosperms) in spring and my conifers (gymnosperms) in Aug/Sep. It nicely balances my work load (a strange term to be attached to a hobby, huh?). I remain curious about the topic, but my aims are to make bonsai. It is my hobby. I'm not really interested in finding funding for my one-man horticultural research institute  :D.
 

Potawatomi13

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Re: How is Root Pruning Possible?
« Reply #11 on: January 27, 2017, 01:50 AM »
Larch exception to:  "If you re pot a Larch after the buds have burst then you could well lose the tree"

In about 1959 when much younger wanted a couple young trees by roadside.  Uncle pulled up 2 young Ponderosas and one young Larch.  It was September.  All survived until about 1990. Soil was regular red roadside dirt so some root damage was done.  Is possible to imagine Larches "could" be repotted at sub optimal time and survive.
 

geoffhobson

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Re: How is Root Pruning Possible?
« Reply #12 on: February 01, 2017, 10:03 AM »
It does depend on the age of the tree. Old larch should never be re pottd once bud has burst, broken pot excepted of course.
It also depnds on root disturbance.