Pruning Hibiscus syriacus

Discussion in 'Outdoor Gardening in the Pacific Northwest' started by dt-van, Aug 23, 2019.

  1. dt-van

    dt-van Active Member 10 Years

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    I have two large Hibiscus syriacus:
    Aphrodite: 7'h x 8'w (a standard tree form with 4 main ascending branches starting 20" from ground).
    Red Heart: 9.5'h x 12'w (a large shrub with one main ascending trunk and a large side branch/trunk)​
    Both are attractive and flower extravagantly, but both are also getting much too broad and tall. I chose Hibiscus syriacus because they are said to be easy to keep pruned to the size you want, but our results with the pink Aphrodite have been disappointing. Light annual pruning made little difference, so we gave it a more severe pruning (branches cut back by about 1/3) last fall. This year it is bigger than ever, but the new growth is more thin and droopy, so the plant spreads even wider and the lower branches sag in the rain.
    I want natural looking plants, that don't look obviously pruned, but I need to keep them narrower than their current width and prefer the original more horizontal/ascending branching pattern.
    Do I just need to prune much harder (eg back by 1/2 or more)? Or should I be pruning later in the fall, or in the early spring. Is there anything I can do to discourage floppy branching?
     
  2. Ron B

    Ron B Paragon of Plants 10 Years

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    Prune to short stubs at end of winter. Resulting tops bloom the same - and have same habit - as unpruned but are much smaller. Don't, of course cut below the height of the existing head on the one with the trunk or you will be removing/shortening the trunk.

    As long as plants are doing well, have good vigor you can do this every year. If still not satisfied with outcomes then you should move them to where they have more room to develop.
     
  3. dt-van

    dt-van Active Member 10 Years

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    Just want to clarify what you mean by
    The 'standard' Aphrodite has 5 steeply ascending main branches with side branches starting at about 30" from the ground.
    If I want the tree to be about 5.5' high when it blooms, should I cut all these off at about 4' high this fall and then cut all the remaining side branches down to stubs. How long should the the stubs be - 2", 4", 6" ?
     
  4. dt-van

    dt-van Active Member 10 Years

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    Just realized that you said "end-of winter" not fall. For Vancouver would late February be a good time?
     
  5. Michigander

    Michigander Active Member

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    You are fighting a losing battle. Every year, the root system has some amount of energy that it can use to inflate some amount of buds/leaves. Every year, the canopy grows, and the roots grow, and they store more energy than the year before. See where this is going?

    Bonsai are kept small by reducing the canopy and roots, regularly. You can buy anything you want, and wish it would keep to any size you want, but nature will win and plants will revert to whatever native traits they have the minute you stop aggressively preventing that. The sooner you move them to where 10 feet high and 6 feet wide is the proper size, the better.
     

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