How to Prune Your Tree
See also: Tree Removal & Pruning and Caring For Your Tree
IMPORTANT: Street trees (located between the sidewalk and street) are public property, just like sidewalks. You must obtain a FREE permit prior to pruning or removing a street tree by calling 408-794-1901.
You may also see the following links:
- Getting Permits
- OCF Tree Pruning Guide (Spanish) - information sheets with pictures.
- Tree Service Companies (pdf) approved by the city of San Jose's Arborist Office.
Five Key Steps for Pruning Young Tree
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 only be 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 be allowed for balanced branch distribution around the central leader. Leave small branches close to scaffolds as temporary branches and cut back or remove 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.
Reasons to Train Young Trees
Done right, pruning can improve the health and appearance of your trees. Whether it's keeping a large-growing species in scale or giving a shaggy tree a trim, smart pruning makes a tree look better. Some trees show their attractive bark or flowers more effectively when pruned. It is also a good idea to cut off water sprouts and suckers for neatness.
Pruning can also help protect a tree's health. Diseased branches sometimes can be removed before they infect the rest of the tree. (Be sure to dip the pruning blade in a 10 percent bleach solution between each cut made to avoid spreading disease.) Dead or broken branches can be removed before insects make a home in there.
Sometimes you need to prune your tree to remove potentially dangerous branches. For example, trimming branches that threaten power lines avoids serious problems, but should be a task for a pro. Large dead or dangling branches should be removed, as well as branches that could interfere with vehicles or lawnmowers. Branches that contact the house on windy days should be cut before they cause damage.
When to Prune
The timing of pruning is influenced by several factors.
• Trees that have just leafed out in spring could be weakened by pruning too early. Pruning in late summer will prevent weakening.
• Pruning for structure and form is best left until the leaves fall and the branches can be seen clearly.
• Remove dead wood in the summer when leafless branches are easily spotted.
• Major pruning should not be initiated during "maple sugar time" (January through early March in most areas).
• Beetles that infect oak trees are active from late spring through midsummer. If oak wilt is present in your region, do not prune your oaks during this period.
• Pruning for clearance should be done when branches are sagging to their lowest point.
What to Avoid
Don't cut too close to the trunk. Flush cuts are too large and delay the sealing of the wound.And don't cut too far from the trunk, leaving an ugly stub, which can give insects an entry point. The wound cannot seal until the stub is removed.
Instead, make the cut just outside the branch collar (the swollen area where the branch meets the trunk). The branch collar contains chemicals that speed the formation of callus tissue that seals the wound.
Making the Cut
Remove large branches in three steps:
1. Make a shallow cut on the underside of the branch, about 4 or 5 inches from the trunk.
2. Cut the branch off about 2-3 inches from the initial cut. When the weight of the unsupported branch causes it to fall, the initial cut keeps the bark from peeling down the side of the trunk.
3. Make the final cut, removing the remaining stub. Make this cut just outside the branch collar, the slightly swollen area where the branch and trunk are joined together.
Preventing V-Shape Crotches and Dealing with Them After the Fact
Narrow, V-shape crotches are inherently weak and are subject to breaking off in wind or ice storms. To prevent V-shape crotches from causing problems, remove one of the stems while the tree is young. If you are wanting to perform corrective pruning on a tree that has a V-shaped crotch, make your first cut 4-5 inches above the union of branches, then make the finished cut about 1/4-inch above the union. On larger limbs that were pruned too late, cut one side back to a lateral branch so that the other side begins to dominate.
Some trees naturally tend to form narrow, V-shape crotches, but not all require corrective pruning. Native elms, hornbeams, serviceberries, hickories, and Osage orange trees are generally strong or small enough that little corrective pruning is needed for structural purposes, except to remove crossing branches that might rub.
Others, particularly maples, flowering pears, ashes, and light-wooded willows and basswoods, should be watched closely and given early training so they avoid structural problems as they grow larger. Bradford pears are notorious for developing weak crotches because too many limbs often form at one point on the trunk. If these limbs are thinned early, when the trees are small, many more can be saved from storm damage.
The following is a list of trees that tend to form V-shaped crotches.
• Basswoods (Tilia spp.)
• Elms (Ulmus spp.)
• Flowering pears (Pyrus calleryana)
• Hackberries (Celtis spp.)
• Hornbeams (Ostrya spp. and Carpinus spp.)
• Locusts (Gleditsia spp. and Robinia spp.)
• Mulberries (Morus spp.)
• Osage oranges (Maclura pomifera)
• Redbuds (Cercis spp.)
• Serviceberries (Amelanchier spp.)
• Some ashes (Fraxinus spp.)
• Some hickories (e.g., Carya cordiformis)
• Some maples (e.g., Acer saccharum, A. saccharinum)
• Willows (Salix spp.)
• Zelkova (Zelkova spp.)
What to do about Suckers
As a survival instinct, some trees sucker up from the ground after they are felled. When the multiple stems grow, they become more prone to storm damage. The natural shape of the tree is compromised as well.
To prevent this, save the straightest stem and remove all others. If you want to grow trees in clump form for aesthetic reasons, make sure the multiple stems are well spaced and that they spread away from one another so they will not rub as they grow larger.
What to do about Forked Trunks
Forked trunks are less stable than a single trunk and often grow together, leaving a hollow cavity where insects and rot can further weaken the tree. The tree will eventually split, or one of the trunks will break off.
When a forked tree is still young, it is important to remove one of the forked trunks young. Cut as close to ground level as possible, making the cut at a slight angle so rainwater drains off the stump. Take care not to damage the bark on the remaining trunk.
Pruning Around a Bud
When cutting back stems, avoid making the cut halfway between buds. This leaves a long portion of the stem to wither and die, which is unsightly and invites insects and disease. Instead, make the cut about 1/4-inch above a bud. Choose a bud facing the direction you wish new growth to follow, and angle the cut in the same direction.
Pruning When Branches Are Growing Together
Too many branches bunched together are unsightly, and can cause problems. What's more, smaller, undesirable branches interfere with the development of larger branches. Thinning these lateral shoots will let the remaining branches get better air circulation, water, and sunlight. This is especially important with trees that tend to form multiple crotches at a single point on the trunk, creating a weak zone.
What to Do About Stubs
When a branch breaks off in the wind, or is cut too far from where it joins the tree, a stub remains. This dead remnant prevents a protective callus from closing the wound and provides insects with an entry point. Once insects make inroads, moisture and rot can take over. If you see discolored wood in the stub, it means the tree was damaged from rot spread. When cutting off an old stub, be careful not to cut into the swollen callus tissue forming at the base of the stub. It's needed to seal the wound.
Dressings sometimes retard the growth of callus tissue (the swollen area) and may trap moisture. Most arborists now use tarlike wound dressings only for special purposes. Some insecticidal wound applications might be used, for example, to discourage beetles from visiting and possibly spreading oak wilt disease. Other products may be used to inhibit regrowth, or suckering, from the pruning wound. Some applications may allow regrowth, but at a reduced rate. These plant growth regulators are frequently used when pruning trees under power lines. The treatment allows the tree to regrow, but lengthens the time before another pruning cycle is necessary.