Spurring new growth on winter branch die-back

Discussion in 'Maples' started by David Hickman, Apr 6, 2018.

  1. David Hickman

    David Hickman New Member

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    Hi. My maples are in full bloom here in Oakland, CA and most are doing well but a couple had quite a few branches that appear to have died during the winter. One maple (8 yr old - Toyama Nishiki) has lost a lot of growth on the uppermost branch and it would be a huge setback to lose this branch. There are still a couple of twigs with growth but approximately 60%-80% of the twigs on this branch didn't come back. Other branches were also affected but are not as integral to the overall shape of the tree.

    Note that I did repot in January and reduced the rootball by about 1/4-1/3 since last year it did not have as much foliage as usual. I have just fertilized with a 3-3-3 bonsai fertilizer mix that I happened to have on-hand.

    I know that I'm supposed to wait until early summer before pruning but I want to know if removing the deadwood now would encourage new growth from that main branch? Do I risk lots of sap bleed-out by removing deadwood now? Is there anything else I can do to encourage new growth or should I just leave it alone until summer and let nature take it's course?

    Thx in advance. Dave
     

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  2. 0soyoung

    0soyoung Rising Contributor

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    Removing deadwood will have no direct effect on the rest of the tree. It can be removed most anytime. Since it may be diseased, be sure to sterilize your pruner afterwards.

    New growth consumes a lot of carbohydrate reserves, so one does not want to prune until well after the new foliage has hardened. Then it is photosynthetically active and can pay back the carbo debt. Hardened foliage also exports more auxin than unhardened which stimulates root growth. Pruning soft new growth obviously weakens the tree in two ways. Removing these auxin sources by defoliation or branch decapitation causes an abrupt drop in auxin levels in the branch, releasing interior buds (called - 'back budding' in bonsai or 'stimulating new growth' in gardening). A dead branch has no auxin sources.
     
  3. David Hickman

    David Hickman New Member

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    Thanks, Osoyoung. That is a great explanation of why pruning has the effect that it has. From what you say, it sounds like removing the branches that failed to bud out this spring will neither hurt the tree nor cause any new growth.

    It sounds like back-budding is what I need to stimulate. Is this best achieved in Spring or early Summer?
     
  4. 0soyoung

    0soyoung Rising Contributor

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    In my climate, it is sometime in May and in August. You should notice that shoots extend and continue to extend, then stop. Give it a week or two in this seeming stasis, then prune. Always leave a leaf pair (i.e., a node where opposing leafs occur). You are not obliged to cut this far back, just don't cut back any further. Just nip off the tip if you want. Regardless, the most distal bud pair will produce shoots.

    I've noticed that pruning in August produces a pair of shoots with a very narrow angle, whereas the angle is wider in May. The widest shoot angles (close to 90 degrees / perpendicular) occur when the over-wintered buds break in spring. Of course, the shortest internode is the first one in spring. You likely only care about this if you are working on bonsai.

    I do structural pruning when the tree is leafless. Right after leaf fall, I cut back to a clearly a visible pair of buds. Buds closer to the trunk will strengthen over the winter. If I need to shorten further, I could cut back again in spring to a visible pair of buds or wait until May (if I want a narrower angle forking).

    The frost-thaw cycles on the sides of winter cause amylase to convert stored starch back into sugar. Living cells dispersed throughout the live wood (i.e., those cells that make live-wood be alive) dump some of this sugar into the xylem lumens (the empty dead wood cells that carry water and minerals up the tree). Osmosis then produces a trunk pressure which is the source of the famous bleeding. Bleeding is actually innocuous and the sugary sap easily washes off with water. This is, after all, how we come to have maple syrup. But, if you've started pruning and it causes you discomfort seeing it happen, wait a week or so to resume pruning - it won't bleed anywhere near as much, if at all.

    My trees are generally just breaking bud now. It has been unusually cool for the last couple of weeks which has prolonged my wait.

    Soon.
     
  5. David Hickman

    David Hickman New Member

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    Great tips. Thanks!
     

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