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I have many large 20-25 feet scrub oak trees on my property. I would like to thin and prune them from the tops in order for them to look like the lower scrub oak I have seen in the area, about 10-15 feet. How low can I cut them from their tops without injuring them and what is the best time of year to do so?

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The best way to prune a tree that has grown out of its space and is too tall is to use a method called crown reduction or drop crotch pruning.  This method is preferred over topping or pollarding because it is healthier for the tree and the tree keeps a more natural appearance.  When making the pruning cuts you want to cut back to lateral branches that are at least 1/3 of the diameter of the limb that is being removed.  Once you have identified which branches you want to remove you will want to follow these steps:

 With the first cut, make a notch on the side of the stem away from the branch to be retained, well above the branch crotch.

  1. Begin the second cut inside the branch crotch, staying well above the branch bark ridge, and cut through the stem above the notch.
  2. Cut the remaining stub just inside the branch bark ridge through the stem parallel to the branch bark ridge.

 This method of pruning will help make sure that you do not damage stem tissue when removing the branch.  As with all types of pruning you want to avoid flush cuts, cutting the branch off flush with the trunk and stub cuts, leaving a short stub of the branch on the tree.  Both flush cuts and stubs can contribute to increased stress and disease in your trees.  

 For most trees the best time to prune is when they are dormant.  Fall is the most common time to prune trees.  Pruning trees during this time will allow you to see the structure of the tree and help you decide where you will make pruning cuts.  This will also reduce the chance of spreading diseases and excessive sap flow.

 

You can find more information, including illustrations of proper cuts and definitions of pruning terms, by following this link to the USDA Forest Service guide on how to prune trees.  http://www.na.fs.fed.us/spfo/pubs/howtos/ht_prune/htprune.pdf

 

Posted on 17 Oct 2007

Heidi Wayman
Horticulture Intern, Salt Lake County

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