Quick answer
Tree pruning is the selective removal of branches from a tree for a stated purpose, such as removing dead wood, improving structure or clearing a path, using cuts placed just outside the branch collar so the tree can seal the wound.
The International Society of Arboriculture says no branch should be removed without a reason, because each cut can change how a tree grows. Pruning differs from topping, which cuts branches back to stubs and is called the most harmful pruning practice known.
Quick facts
The key facts about Tree Pruning, with sources:
- Core rule
- No branch should be removed without a reason, because each cut can change the tree’s growth 1
- Where the cut goes
- Just outside the branch collar; the collar is trunk or parent-branch tissue and should not be damaged 1
- Amount per visit (ISA)
- Generally no more than 25 percent of the crown at once, and less for mature trees 1
- Amount per visit (Nebraska)
- Never more than about 20 percent of the crown’s leaf area 4
- Cut size (Colorado State)
- Ideally cuts of two inches in diameter or less; avoid cuts over four inches without strong reason 3
- Topping
- Can remove 50 to 100 percent of the leaf-bearing crown and leaves weakly attached shoots 2
- Wound dressings
- Research shows they do not reduce decay or speed closure; most experts advise against them 1
Key takeaways
- Start with the reason. A cut with no purpose can still harm the tree.
- The proper cut sits just outside the branch collar. Flush cuts and leftover stubs both hurt.
- Sources set different limits on how much live crown to remove. The lower number is safer, and older trees tolerate less.
- Topping is not pruning. It cuts to stubs and leaves weak regrowth that breaks.
- Work that is high, large or near power lines belongs to a qualified arborist. This page gives no climbing or saw instructions.
Pruning is a decision about the tree, not about the branch
ISA’s consumer brochure calls pruning the most common tree maintenance procedure. It adds that forest trees grow well with only nature’s pruning, but landscape trees need more care to keep their structure and looks. It also warns that improper pruning can create lasting damage or even shorten a tree’s life 1.
The same brochure says no branch should be removed without a reason, because each cut has the potential to change the tree’s growth 1. Common reasons are to remove dead branches, improve form and reduce risk. Others are to let light and air into the crown or to clear space below 1.
Routine thinning does not necessarily make a tree healthier. A tree makes sugar in its leaves, and removing foliage can reduce growth and stored energy, so heavy pruning can be a significant health stress 1.
This page owns the definition and the proper cut. For how thinning and reduction differ, see crown thinning vs. crown reduction. For small woody plants, see shrub pruning.
Where the proper cut goes, and why
The is below the logic of the cut, not a how-to for doing it. The branch collar is the swollen ring of tissue where a branch meets the trunk or a larger limb.
- The collar holds the tree’s defence. ISA says the branch collar contains trunk or parent-branch tissue and should not be damaged or removed 1. Colorado State adds that the natural defense boundaries sit just under it 3.
- The cut goes just outside the collar. ISA says pruning cuts should be made just outside the branch collar. Nebraska says to start just outside the branch bark ridge and angle away from the stem 14.
- If the collar has grown out on a dead limb, cut beyond it. ISA says to cut just beyond the grown-out collar and not cut the collar itself 1.
- A flush cut removes the collar. Nebraska says not to make flush cuts that remove the branch collar. A stub is the other error: ISA says a stub leaves an open pathway for decay 42.
- Big limbs take staged cuts. ISA describes relieving a large limb’s weight before the final cut to avoid tearing bark 1. That is work for a trained crew with the right gear.
- Stub left too longLeaves an open pathway for decay 2
- Proper cutJust outside the branch collar, angled away from the stem 14
- Branch collarSwollen ring of trunk or parent-branch tissue; leave it intact 1
- Flush cutRemoves the collar and defense boundaries; avoid 43
- Trunk or parent limbThe wood the cut is meant to protect
Positions follow ISA, Nebraska Forest Service and Colorado State guidance. This is a diagram of ideas, not a cutting guide. Source: [1] [4] [3] [2]
Anything high, large or near power lines is for a qualified arborist
ISA says that pruning large trees can be dangerous, and that work above the ground or with power equipment is best given to a professional arborist with a trained crew, safety equipment and liability insurance 1.
Nebraska notes that even highly skilled arborists have been seriously injured pruning large trees 4. Stay away from any limb or tree touching or near a power line. Call the utility, not a ladder.
The pruning types arborists name
| Type | What it removes | Purpose | Source note |
|---|---|---|---|
| Cleaning | Dead, dying, diseased, weakly attached and low-vigor branches | Risk and health | ISA; Colorado State says all dead wood can go at once and does not count toward the live-wood dose 13 |
| Thinning | Selective small branches | Light, air movement and less weight on heavy limbs | ISA; Colorado State says thinning removes branches about 1/2 inch to 2.5 inches across in the outer crown 13 |
| Raising | Lower branches | Clearance for buildings, vehicles, people and views | ISA; Colorado State advises keeping at least half the foliage in the lower two-thirds of the tree 13 |
| Reduction | Height or spread, by cutting back to a side branch that can take over | Size control, often for utility clearance | ISA says the receiving branch should be at least one-third the diameter of the cut stem 1 |
| Structural pruning | Weak secondary trunks, subordinated to a dominant trunk | Lower failure risk over years | Colorado State; works best as annual work over several years 3 |
| Restoration | Sprouts and stubs left by storms or poor pruning | Rebuild structure | Colorado State; usually spread across years 3 |
How much can come off at once? The sources disagree
| Source | Figure it prints | Scope | What to take from it |
|---|---|---|---|
| ISA, Pruning Mature Trees | Generally no more than 25 percent of the crown at once, and less for mature trees 1 | General consumer guidance | Treat it as a ceiling, not a target |
| Nebraska Forest Service | Never more than about 20 percent of the total leaf area of the crown, for live branches 4 | Landscape trees | Slightly tighter than ISA |
| Colorado State, mature trees | 5 to 10 percent, based on growth and vigor, for trees past 75 percent of mature size for the site 3 | Mature shade trees | Much lower for old trees |
| Colorado State, medium-aged trees | 10 to 25 percent, depending on growth and vigor 3 | Medium-aged trees | Depends on how fast the tree grows |
| Colorado State, stressed trees | Cleaning only; no live wood on severely stressed or drought-stressed trees 3 | Trees with very little yearly growth | Stress changes the answer |
Example: reading a pruning bid against a written spec
Colorado State says a written pruning specification should name the tree, the objectives, the methods, the cut-size limits, the dose, and the standards followed 3. The bid lines below are invented to show what a clear line and a vague line look like.
| Bid line (example) | What is missing or present | What Colorado State and ISA would ask |
|---|---|---|
| Trim oak in back yard | No objective, no method, no amount | Why prune, which method, and how much live crown 3 |
| Clean dead wood 2 inches and larger from front maple; no live wood removed | Objective, method and size limit are all stated | Matches the cleaning type, which does not count toward the dose 3 |
| Reduce spruce height by one-third | Method named, but no mention of the side branch size or the standards | Is each cut back to a branch at least one-third the diameter of the cut stem 1 |
| Top the silver maple | Topping | Do not accept. ISA says topping is not an acceptable pruning technique 2 |
Ask who will do the work and under which standard. Compare lines with our landscaping estimates guide, and see tree service for what a full job includes.
Where the term shows up: bids, storms and utility notices
On a tree service bid. You will see trimming, pruning, cleaning, thinning, raising and reduction. Ask what each line means and for the objective in writing.
After a storm. Nebraska says to remove only broken branches right after a storm and save fine and finishing cuts for later 4. Colorado State says to wait for roots and crown to stabilize before major structural work 3.
In a utility letter. Colorado State says pruning for line clearance does not always follow good practice for health and looks, because the line’s needs take priority. It suggests removal and replanting when a tree under a line needs frequent reduction 3. Utility crews do that work, not you.
In a risk report. A tree risk assessment may call for pruning. See tree risk assessment and cabling and bracing.
What good pruning does, and what it cannot
What it can do
- Removes dead, diseased or weakly attached branches that could fail 1.
- Improves structure when started early. Colorado State says structural problems are best fixed when the tree is young 3.
- Lets light and air through and provides clearance for buildings and paths 1.
- Done right, keeps natural form. ISA says reduction preserves a tree’s form better than topping 2.
What it cannot do
- Cannot make a tree healthy by itself. ISA says routine thinning does not necessarily improve health 1.
- Cannot fix every structural fault late. Colorado State says arborists have limited ability to correct defects on mature trees without causing decay and cracking 3.
- Cannot permanently shrink a large tree. Colorado State says it is very hard to keep a tree small by reduction without causing decline 3.
- Cannot be undone. Wounds and lost foliage stay for years.
Limits and open points
The numbers above are guidelines from three publishers, and they differ. We did not find one national figure for how much to remove, and the standards that arborists follow are not free to read. We describe their framework through ISA and Colorado State only.
Colorado State’s guide is written for mature shade trees in Colorado and warns that some trees cannot be reduced without decline 3. Its examples about cottonwood and poplar do not transfer to every species.
The ISA brochure we read is the 2011 edition, hosted by a city. ISA says it revises its brochures, so wording may have changed. We found no source that sets a fixed pruning calendar for all trees.
We also found no study we could cite that ranks pruning methods by cost or by long-term tree health across species.
What drives the price of pruning, and how often it recurs
We do not publish prices. A bid moves with tree height and spread, the species, how much dead wood is up there, access for a crew and equipment, the type of pruning, and cleanup and haul-off. Work near power lines may require a utility or a specially qualified crew.
Insurance and safety gear are part of the price of a professional. ISA says an arborist can provide a trained crew with the required safety equipment and liability insurance 1. Ask for proof of insurance before the work.
Frequency depends on the tree. Colorado State says annual pruning is the ideal for structural work, and that a tree pruned only every few years may need heavier work 3. We give no schedule.
Compare a trim with a removal using the tree removal cost tool and see what sets a bid in the cost hub.
Who does the work, and how to ask for a written spec
For anything beyond small branches you can reach safely from the ground, hire an ISA Certified Arborist. Colorado State recommends looking for ISA certification and asking about liability coverage 3. Use this list to ask for a clear job.
- Name the tree or trees, and the objective: risk, structure, clearance, health or view 3.
- Ask for the method: cleaning, thinning, raising, reduction, structural or restoration 3.
- Ask for the largest branch size to be cut and the share of live crown to be removed, so the bid shows a limit 3.
- Ask that cuts follow the pruning standard the arborist uses, and which one it is.
- Ask who is on the crew, their insurance and who is on site to supervise.
- Say no to topping, spiking, stubbing and wound paint. ISA says dressings do not reduce decay or speed closure 12.
Check licensing where you live
Tree work licensing varies by state and city. The landscaping licensing by state page shows what we verified. Our guide to choosing a company lists questions to ask.
Aftercare: what the sources say and do not say
Upkeep tasks are listed here without fixed dates.
- Skip wound paint. ISA says most experts recommend that wound dressings not be used 1. Nebraska says never use paint or wound dressing 4.
- Watch for waterspouts. Colorado State says excessive pruning leads to waterspouts, which are structurally unsound 3.
- Recheck stressed trees. Colorado State says trees under stress or declining may need cleaning every few months to every few years 3.
- Protect the root zone. Pruning does not help a tree with damaged roots. See critical root zone.
- Keep mulch off the trunk. ISA says to pull piled mulch back so the base of the trunk is exposed 5. See the tree mulching entry.
Warning signs, and when to call a professional
- A branch that is dead, cracked or hanging. Do not stand under it. A qualified arborist should assess it 3.
- Branches touching or near a power line. Call the utility. Do not prune near lines.
- A tall tree or a large limb. ISA says pruning large trees can be dangerous 1.
- A tree that has been topped. Colorado State says the regrowth is structurally unsound 3. A qualified arborist can plan restoration.
- A storm-damaged tree. Nebraska says to remove only broken branches at first, and that branches or trunks that lost more than a third of their original circumference to bark stripping should be removed 4.
For a tree you worry about, a qualified arborist can assess it. That visit usually starts with an on-site assessment.
Standards, laws and local rules
A voluntary standard. Arborists follow the pruning part of the ANSI A300 standards for tree care.
Colorado State says heading cuts are not acceptable in pruning standards, and that under ANSI standards a cut back to a side branch smaller than one-third the diameter is a heading cut 3.
A standard is voluntary until a contract, specification or law adopts it. We did not read the standard itself.
Local law. Cities often regulate protected trees, street trees and removal. Our tree removal permit research, linked in the local section, covers removal, and the same offices can tell you if pruning needs a permit.
Utility rules. Line clearance follows the utility’s own standards. Colorado State says the utility’s needs take priority over the tree 3.
HOA rules. A neighborhood association may limit species or removal. See HOA landscaping research.
Common pruning myths
- Myth Cut a tree’s top to keep it small.
- Reality ISA says topping is not a viable method of height reduction and will increase risk in the long term 2.
- Myth Paint the cut to protect it.
- Reality ISA says research shows dressings do not reduce decay or speed closure 1. Nebraska says never to use them 4.
- Myth Thinning the crown always helps a tree.
- Reality ISA says routine thinning does not necessarily improve health 1. Nebraska notes it can stress trees in summer 4.
- Myth Cut flush to the trunk so it heals faster.
- Reality Flush cuts remove the branch collar and the natural defense boundaries 43.
- Myth Winter is the only time to prune.
- Reality ISA says most routine pruning can be done at any time, though growth and wound closure are best before the spring growth flush 1.
The regional variable: oak wilt and local timing
Timing is one place the rules vary by region. ISA says a few tree diseases, such as oak wilt, can spread when pruning wounds give pathogens access, and that susceptible trees should not be pruned during active transmission periods 1.
Nebraska says that in areas where oak wilt is a concern, pruning of oaks should be restricted from April through June 4.
Your state forestry agency or extension office knows whether oak wilt is active near you. We give no national calendar. For city rules on protected trees, see the permit research.
When to prune, and your next step
Prune when you can name a reason: dead wood, a hazard, a structural fault or clearance. If you cannot name one, waiting is often fine.
Your next step is to stand back and write the reason. Then decide if the work is on the ground, small and safe, or high, large or near lines. For the second group, call a qualified arborist and ask for a written spec.
If you are weighing removal instead, the removal cost tool in the cost section helps. For thinning or reduction, read the crown thinning page first.
Questions about Tree Pruning
What is tree pruning?
Tree pruning is the selective removal of branches for a stated purpose, such as dead-wood removal, better structure or clearance, using cuts just outside the branch collar. ISA says no branch should be removed without a reason, because each cut can change how the tree grows.
Where do you cut a tree branch?
ISA says cuts should be made just outside the branch collar, the swollen ring of tissue at the branch base. Nebraska says to start just outside the branch bark ridge and angle away from the stem. Do not make flush cuts that remove the collar, and do not leave a long stub.
What is the branch collar?
The branch collar is the slightly swollen ring of tissue where a branch meets the trunk or a larger limb. ISA says it contains trunk or parent-branch tissue and should not be damaged. Colorado State says the tree’s natural defense boundaries sit just under it.
How much of a tree can you prune at once?
Sources differ. ISA says generally no more than 25 percent of the crown at once, and less for mature trees. Nebraska says about 20 percent of the leaf area. Colorado State gives 5 to 10 percent for mature trees and 10 to 25 percent for medium-aged ones, depending on vigor.
Why is topping a tree bad?
Topping can remove 50 to 100 percent of the leaf-bearing crown, per ISA. It can starve the tree, leave stubs that decay, expose bark to sunburn and trigger weakly attached shoots that break in wind or ice. ISA says topping increases risk in the long term.
When is the best time to prune a tree?
ISA says most routine pruning can be done any time, with growth and wound closure best before the spring growth flush. Nebraska prefers winter and warns against the spring flush and fall color change. Where oak wilt is active, avoid pruning oaks in the active period your state advises.
Should I paint or seal pruning cuts?
No. ISA says research shows wound dressings do not reduce decay or speed wound closure, and most experts recommend not using them. Nebraska’s guidance says never to use paint or wound dressing on pruning wounds.
Can I prune trees near power lines myself?
No. Keep away from branches near or touching lines and call the utility. ISA says pruning large trees can be dangerous and that work above the ground or with power equipment is best left to a professional arborist. A utility crew handles line clearance.
What is the difference between pruning and trimming?
People use the words interchangeably. Arborists use pruning for work done for a purpose with proper cuts, and name the type: cleaning, thinning, raising or reduction. A bid that says only trim should be rewritten with the objective, method and amount.
How do I find a qualified arborist?
Colorado State says to look for arborists certified by the International Society of Arboriculture and to ask about liability insurance. Ask for a written spec that names the tree, objective, method, cut-size limit and amount of live crown to remove. Check local licensing where you live.
Sources
- International Society of Arboriculture, Pruning Mature Trees (TreesAreGood consumer brochure, 2011 edition), PDF as hosted by Seattle Department of Transportation, read as text, retrieved .
- International Society of Arboriculture, Why Topping Hurts Trees (TreesAreGood consumer brochure, 2011 edition), PDF as hosted by Seattle Department of Transportation, read as text, retrieved .
- Colorado State University Extension, CMG GardenNotes #615, Pruning Mature Shade Trees, PDF as hosted by Adams County Extension, read as text, retrieved .
- University of Nebraska-Lincoln, Nebraska Forest Service, Pruning Trees, retrieved .
- International Society of Arboriculture, Proper Mulching Techniques (TreesAreGood consumer brochure), PDF as hosted by Seattle Department of Transportation, read as text, retrieved .
Expert review
Written by the HyreYard Research Desk. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: The branch-collar rule, pruning types, 25 percent guideline, wound-dressing advice and arborist guidance come from the ISA Pruning Mature Trees brochure, a 2011 edition read as text from a city-hosted PDF.
Topping facts come from the ISA topping brochure. Cut-size, dose and mature-tree limits come from Colorado State CMG GardenNotes #615, read as text from a PDF. The 20 percent figure and timing come from the Nebraska Forest Service page.
Standards are described only as those sources describe them. The bid examples are invented and labeled. No saw, climbing or power-line instructions are given and no prices appear.
Suggest a correction. We fix errors and say what changed.