Pruning – prune only for a reason!
Trees themselves do not "need" pruning; humans need to prune trees according to the various uses we have for them. We prune a fruit-bearing tree to bear large, healthy, easy to reach fruit. We prune a backyard tree to screen neighbors or allow views to peek through. We prune a street tree to stay out of the way of the street cleaning truck and of pedestrians, and to have a safe and sound structure. Be sure you are clear on your reason(s) for pruning before you start and your job will be much easier. If you have no reason, maybe it’s better to leave it alone!

Pruning a tree allows you to be an artist and a craftsperson. Before touching the tree, step back and look at it. Walk into the middle of the canopy and look up. Good pruning follows the natural form of the tree, which could be round, weeping, upright, oval, spreading or irregular. The purpose of pruning is to enhance the natural shape, direct growth, create free wind passage, and encourage sound structure. A few small cuts when the tree is young can prevent expensive chainsaw corrections later on.

These are links to further down on the page

Training young trees
Street tree guidelines
General principles of pruning
Retraining a central leader that has broken
Further resources – Tree City USA, Urbantree.org, ISA

Training young trees – 5 steps
(from UC Agriculture/Natural Resources video entitled Training Young Trees for Structure and Form)

1. Remove broken, dead, dying, diseased, or damaged branches. Inspect the canopy and remove or cut back these branches.
2. Select and establish a central leader. There should be only one leader. Select the strongest and most vertical stem as the leader and remove or cut back competing stems.
3. Select and establish the lowest permanent branch. Look for a well-attached branch at the desired height (determined by location and use), and remove closely spaced, competing branches. The diameter of the lowest permanent branch should be no more than one-half that of the central leader or trunk (at the point of attachment). Smaller temporary branches should be left close to the lowest permanent branch. Larger temporary branches should be pruned back to one or two buds.
4. Select and establish scaffold branches. Look for well-attached branches above the lowest permanent branch that are no more than one-half the diameter of the central leader. Scaffold branches should be well spaced both vertically and radially. Vertical spacing should be 18 inches or more for large trees and 12 inches for smaller trees. Radial spacing should allow for balanced branch distribution around the central leader. Leave small branches close to scaffolds as temporary branches and remove or cut back larger branches.
5. Select temporary branches below the lowest permanent branch. Some or all the branches below the lowest permanent branch can be retained as temporaries. If possible, leave the smallest branches and cut back or remove the largest branches. If a temporary branch is more than the diameter of the trunk, cut it back by at least 50% to discourage excess growth.
   

ISA, (International Society of Arboriculture) standards dictate that when pruning you should never remove more than 25% of living tree mass. A young tree can handle a bit more being removed, say up to 1/3, but only do so if there is a good reason.

Street tree guidelines
When pruning street trees, consider city codes for clearances. Department of Public Works requires that the tree have a canopy at least 14’ up on the curb side and at least 8’ up on the pedestrian side. Obviously, a young tree will be too small to prune to these specs, so keep in mind that pruning is an ongoing process.

General principles of pruning
There are nine easy steps to remember when pruning. They are the three "D’s", the three "C’s", and the three "S’s".

• DEAD
  First, remove dead branches. Remember that if your tree is deciduous and it is winter, it may be leafless but it could be alive. To check if a limb is really dead or not, scrape the surface with your fingernail. If it is alive it will look greenish underneath and be supple when bent. If it is dead, it will be brown and brittle when bent.
• DISEASED
  This step is the most difficult to ascertain. You may need to call a certified arborist to help you. See our Pest page for more info.
• DAMAGED
  Damaged limbs refer to those hit by cars or broken by rude people. Here is where we see the problems of low limbs meeting tall trucks. The damaged limbs should be removed with a clean cut. You can either cut back to the branch collar at the trunk or cut back to a side branch that is growing in a desirable direction. The side branch should be 1/3 or more the size of the main branch it’s growing from.
• CROSSING
  Crossing limbs will rub and injure each other. Which to remove? Consider which branch adds most to the structure of the tree. An ideal structure is a tree with a central leader and smaller scaffold branches that are well spaced apart and well-attached. Often we remove a crossing branch that is growing into the center of the tree.
• CROWDING
  Are the branches too close? Will they create a problem in the future? If so, make a decision based on removing the weakest or the ones that are pointing in to the center of the tree, are crossing or are competing.
• COMPETING
  This refers to branches that are running parallel and close or are positioned in such a way that they will be weakening the overall use of the tree’s energy. Remember the idea of scaffold branches being positioned radially around the tree. You don’t need two branches growing in the same spot.
• SAFETY
  For street trees this is one of the most important things to keep in mind. Is the tree blocking a sign or a driveway? Is a limb at a place where someone walking by could get poked in the eye?
• SHAPE
  Here you need to understand the natural form of the tree and prune in such a way as to best reinforce that.
• SIGHTLINE
  Similar to considerations taken into account with safety, sightline also refers to whether a tree is blocking a view or path of egress.
  

 
How to make a pruning cut

Now that you are thinking in abstract pruning terms, how do you actually make healthy cuts? The idea is cut close to the main limb without making a flush cut or leaving a stub. Look for the branch collar, the swollen area where one branch meets and cut just to the outside of this place. For small limbs, cut upward.

A correct pruning cut has its lower point even with the top of a growth bud and slants upward at about a 45° angle.

To make a proper close pruning cut, hold pruning shears with the blade closest to the growth that will remain on the plant. A stub results when you reverse the position and place the hook closest to the plant.
 
 

For larger limbs, use three cuts. The first cut is an undercut to the bark from peeling down the trunk when you make the second cut to remove the weight of the limb. The third is your finish cut. Here you must guide your saw just to the outside of the branch collar with clean strokes so the final result is smooth.

First, cut beneath branch, one-third to one-half through; then cut off limb beyond first cut. Finally, remove limb stub, cutting just outside bark ridges at limb's base.

Retraining a central leader that has broken The central leader directs the growth of the entire tree. If it breaks, the largest scaffold branch will attempt to become the new leader. If this branch is not growing upright, the tree may grow in an undesirable direction. You can try to retrain a new central leader.
	1. Find a branch that is pointing as centrally and upright as possible and cut just above that branch.
2. Look at any strong scaffold branches that may attempt to become the new leader. You do not need to remove these branches entirely. Just cutting them back will "discourage" them. You may need to cut the branch a bit more in subsequent years.
	3. Cut back to a lateral (side) branch that is at least 1/3 the diameter of the main branch. In other words, don’t make a cut that leaves you with a large main branch and a tiny sprout coming out of it. The lateral branch you cut back to should look as natural as possible.

Further resources

FUF offers:

• Pruning workshops 4 times a year with a guest arborist lecturer and time for field practice.
• Hands on practice with guidance – volunteer with FUF on the1st and 3rd Saturday of the month, 9:00 a.m.-12:30, when we maintain 18 month and 3-year-old FUF trees.

  For info, call the Tree Care Coordinator at 415/561-6890 x102 or email ellyn@fuf.net
  

Print out these excellent illustrated tree care guidelines in either English or Spanish:
www.arborday.org/programs/treecitybulletins.html

This site contains more detailed pruning info! Very complete and easy to read!
66.165.117.218/pruninglandscapetrees.asp

International Society of Arboriculture
www.isa-arbor.com

This is another educational link about pruning with very good pictures:
www.na.fs.fed.us/spfo/pubs/howtos/ht_prune/approaches.htm

Download a copy of Tree Pruning Standards in the City and County of San Francisco, published by SF Environment (PDF, 13,400 KB)