Leaf reduction by root pruning?

jferrier

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I've read before that root bound trees in pots will develop smaller leaves and start to decline after a while and that pruning is a way to invigorate the plant and encourage new growth. This seems logical as the roots are confined and unable to grow too much so they can't provide an over abundance of food. However, last year I air layered the top half of a vigorous Shin Deshojo maple that had been growing in a large nursery container for 4 or 5 years. The roots of the parent were not completely rootbound, but close. The top layered half ,as would be expected , had many more dormant buds than the lower half. I have both trees in the same type of soil, located just a few feet apart, and receiving the same water and fertilizer. So, this spring when the two put out new leaves, the air layered top half had numerous leaves that are about 1/4 the size of the parent tree. So, I suspect that the small leaves were a result of the tree having numerous buds but less roots to feed them, and the large leaves were a result of the tree having fewer buds and a quite extensive root system pumping lots of energy into far fewer buds than they are capable of supporting. Does this seem logical, or could it be something else?
 

Zach Smith

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I've read before that root bound trees in pots will develop smaller leaves and start to decline after a while and that pruning is a way to invigorate the plant and encourage new growth. This seems logical as the roots are confined and unable to grow too much so they can't provide an over abundance of food. However, last year I air layered the top half of a vigorous Shin Deshojo maple that had been growing in a large nursery container for 4 or 5 years. The roots of the parent were not completely rootbound, but close. The top layered half ,as would be expected , had many more dormant buds than the lower half. I have both trees in the same type of soil, located just a few feet apart, and receiving the same water and fertilizer. So, this spring when the two put out new leaves, the air layered top half had numerous leaves that are about 1/4 the size of the parent tree. So, I suspect that the small leaves were a result of the tree having numerous buds but less roots to feed them, and the large leaves were a result of the tree having fewer buds and a quite extensive root system pumping lots of energy into far fewer buds than they are capable of supporting. Does this seem logical, or could it be something else?

Sounds logical. A tree doesn't care how many leaves it has, just that there's enough leaf surface area to produce the food needed. So you can either have a few big leaves or a lot of little leaves. The number and size usually reflect the root system's complexity, in the same manner that you get ramification in the crown of the tree that reflects the ramification underground. I suspect that, left alone, your layer will tend to revert to fewer bigger leaves as certain roots outcompete others for dominance. The tree will always want to be its genetically predetermined size.

Zach
 

Vance Wood

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I think your assumption is true. However; if you layered above the graft, if there is one, you may be seeing the results of the tree growing on its own genetic root system.
 

jferrier

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I think your assumption is true. However; if you layered above the graft, if there is one, you may be seeing the results of the tree growing on its own genetic root system.

It is layered above the original graft and growing on its own genetic root system. Could it be that the genetic roots aren't as vigorous as the (I'm guessing) green maple rootstock? This then makes me wonder if the characteristics of a particular variety may be changed depending on the root stock.
 

jferrier

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I suspect that, left alone, your layer will tend to revert to fewer bigger leaves as certain roots outcompete others for dominance. The tree will always want to be its genetically predetermined size.

Zach

I think you might be confused. It's my layer that has the small leaves now and the parent has the large leaves.
 

Vance Wood

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It could be that it is indeed its own roots causing the leaf reduction but; it is also possible the existing roots are not yet strong enough to support the upper portion of the tree to its potential. You need to give it a couple of years to determine where it is really going.
 
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