Structural Pruning
Structural pruning is pruning aimed at developing and maintaining a branch structure that is less likely to fail. Colorado State University Extension says it can be done on trees of any age but is most effective on young to middle-aged trees, because their branch structure is easier to change.
Source: Structural Pruning of Young Shade Trees (CMG GardenNotes #613), Colorado State University Extension
What structural pruning aims for
Colorado State sets five objectives for young shade trees: clear out dead, damaged, crossing and rubbing branches; keep one dominant leader reaching close to the top of the crown; hold temporary branches to less than half the size of the limb they grow from and take them out before they reach 2 inches across; select evenly spaced permanent (scaffold) branches and keep each below half the size of its parent; and keep the live crown ratio at 60 percent or higher (the Forest Service guide and Colorado State’s guide to mature trees use two-thirds instead).
Scaffold spacing scales with the tree’s eventual size, at roughly 3 to 5 percent of its expected mature height. Colorado State’s table and figure work from the 5 percent end, which comes to 6 inches of spacing for every 10 feet of mature height, so a tree expected to reach 30 feet gets scaffold branches at least 18 inches apart.
Sources: Structural Pruning of Young Shade Trees (CMG GardenNotes #613) ; How to Prune Trees (NA-FR-01-95, revised 2012) ; Pruning Mature Shade Trees
One dominant leader
Colorado State’s first strategy is to choose one trunk as the dominant leader and remove or shorten every competing leader; shortening a competitor subordinates it to the unpruned leader. Purdue Extension adds a structural-pruning rule: the main leader, or parent stem, ought to be twice as wide as any branch growing from it. Two leaders of equal size are a special case; see codominant stems.
Sources: Structural Pruning of Young Shade Trees (CMG GardenNotes #613) ; Corrective Pruning for Deciduous Trees (FNR-563-W)
When to start and how often
Start at planting, but keep it light. The USDA Forest Service Tree Owner’s Manual says to prune only broken or dead branches at planting, plus competing leaders if there are any, because leaves make the food a new tree needs to recover from transplant shock, so it should keep as many as it can. From 2 years after planting, it suggests light pruning once a year or once every second year.
The Forest Service’s Northeast Community Tree Guide gives a similar schedule: ideally, young trees are checked and pruned every second year for their first 5 years in the ground.
Sources: Tree Owner’s Manual for the Northeastern and Midwestern United States (NA-FR-04-07) ; Northeast Community Tree Guide: Benefits, Costs, and Strategic Planting (PSW-GTR-202)
Temporary and low branches
Branches do not rise as a tree grows. The Tree Owner’s Manual notes that they stay at the same height, so low branches that will get in the way of sidewalks or mowing have to be removed gradually. Until then, the Forest Service guide How to Prune Trees says temporary branches can be kept on young trees to encourage taper and protect them from vandalism and sunscald, pruned each year to slow their growth and removed eventually.
Colorado State puts the lowest permanent branch about 7 to 10 feet up for shade trees in lawns, on patios and along sidewalks, and 14 feet or higher over streets.
Sources: Tree Owner’s Manual for the Northeastern and Midwestern United States (NA-FR-04-07) ; How to Prune Trees (NA-FR-01-95, revised 2012) ; Structural Pruning of Young Shade Trees (CMG GardenNotes #613)
How the ISA arborist exam tests it
Structural pruning questions appear in both the Installation and Establishment and the Pruning domains: how much to prune at planting, how often to prune young trees, and what to do with temporary branches and low limbs that will be in the way. Try 4 reviewed practice questions:
How much should a newly planted shade tree be pruned at the time of planting?
Show answer and explanation
Correct answer: D. Remove only dead or broken branches, plus a competing leader if needed
A new tree needs as many leaves as it can keep, because leaves make its food and help it recover from transplant shock. The USDA Forest Service Tree Owner's Manual says to prune only broken or dead branches at planting, plus competing leaders if present. Cutting back the crown to balance lost roots is the classic wrong answer: Clemson Extension notes that pruning to make up for root loss does not ease transplant shock unless the tree is short of water. Heading cuts and stripping lower limbs also remove needed leaf area.
- A: Pruning to balance root loss is an outdated practice that research does not support.
- B: Heading back tips removes leaf area and produces weak, crowded sprouts.
- C: Removing the lower limbs at planting takes away leaf area the tree needs to establish.
Sources: Tree Owner's Manual for the Northeastern and Midwestern United States (NA-FR-04-07), USDA Forest Service, Northeastern Area State and Private Forestry ; Planting Trees Correctly (HGIC 1001), Clemson Cooperative Extension, Home & Garden Information Center
Report a problem with this question · ID inst-027
A city forester is writing a pruning plan for street trees planted this spring. Which schedule for their first several years best matches USDA Forest Service guidance?
Show answer and explanation
Correct answer: D. Inspect and lightly prune every year or two during the early years
The USDA Forest Service Northeast Community Tree Guide says young trees should ideally get an inspection and pruning every second year through their first 5 years after planting, and the Tree Owner's Manual says to start 2 years after planting and prune lightly once every year or two. Heavy pruning at planting is the tempting way to set the structure early, but the Manual says new trees need every leaf they can get to recover from transplant shock. Waiting until limbs are large makes pruning more costly and riskier for the tree.
- A: The Manual says to begin about 2 years after planting, not after 10 years.
- B: At planting, prune only broken or dead branches; new trees need their leaves to recover.
- C: Both USDA sources start light pruning within the first few years, not at age 10.
Sources: Northeast Community Tree Guide: Benefits, Costs, and Strategic Planting (PSW-GTR-202), USDA Forest Service, Pacific Southwest Research Station ; Tree Owner's Manual for the Northeastern and Midwestern United States (NA-FR-04-07), USDA Forest Service, Northeastern Area State and Private Forestry ; Tree Owner's Manual for the Northeastern and Midwestern United States (NA-FR-04-07), USDA Forest Service, Northeastern Area State and Private Forestry ; Tree Owner's Manual for the Northeastern and Midwestern United States (NA-FR-04-07), USDA Forest Service, Northeastern Area State and Private Forestry
Report a problem with this question · ID inst-057
A young shade tree has several small branches low on its trunk, below where its permanent crown will begin. How do the USDA Forest Service and Colorado State University Extension say these temporary branches should be handled?
Show answer and explanation
Correct answer: B. Keep them small by pruning, then remove them before they grow large
The USDA Forest Service's How to Prune Trees says a young tree may keep temporary branches along its stem to encourage taper and to shield it from vandalism and sunscald, but those branches need yearly pruning to slow their growth, and eventually they should come off. Colorado State University Extension adds that each one should stay under half the size of its parent branch and be cut off before it grows past two inches. Removing them all at planting is the tempting tidy-up, but it gives up those benefits while the tree is young.
- A: Temporary branches are kept on young trees for a time because they encourage taper and give protection.
- C: Letting them grow freely defeats the aim; CSU says to remove them before they grow past 2 inches.
- D: Temporary branches are removed eventually; they are not kept as permanent limbs.
Sources: How to Prune Trees (NA-FR-01-95, revised 2012), USDA Forest Service, Northeastern Area State and Private Forestry ; How to Prune Trees (NA-FR-01-95, revised 2012), USDA Forest Service, Northeastern Area State and Private Forestry ; Structural Pruning of Young Shade Trees (CMG GardenNotes #613), Colorado State University Extension
Report a problem with this question · ID inst-056
On a young street tree, a low branch about 5 feet up already reaches over the sidewalk. The owner wants to keep it, expecting it to rise out of the way as the tree grows taller. What should the arborist explain?
Show answer and explanation
Correct answer: B. It will stay at the same height, so plan to remove it over time
NC State Extension's Gardener Handbook notes that a branch does not get any higher as the tree grows; it keeps the same height throughout its life. Over time, some lower branches must be removed as they lengthen, cast unwanted shade or interfere with traffic, so a low branch over a sidewalk should be treated as temporary. Pruning other branches or trunk thickening will not raise it.
- A: A branch stays at the same height for life; it does not move up as the tree grows.
- C: Removing branches above does not raise a lower branch; its height is fixed.
- D: Trunk growth in diameter does not lift branches; they stay at the same height.
Sources: Extension Gardener Handbook, Chapter 11: Woody Ornamentals, NC State Extension ; Extension Gardener Handbook, Chapter 11: Woody Ornamentals, NC State Extension
Report a problem with this question · ID prun-054
0 of 4 correct
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Common mistakes in the field
Waiting until limbs are large
The Tree Owner’s Manual points out that taking off small branches is simple, while waiting until limbs are big makes pruning more costly and a greater risk to the tree. Colorado State keeps cuts at 2 inches or smaller where possible and reserves cuts over 4 inches for cases where no other option meets a critical pruning objective.
Raising the crown too high, too fast
Colorado State warns against raising a young tree too high or too quickly: lower limbs supply energy for proper trunk taper and help spread the wind load, so they should be kept short and removed gradually.
Pruning the central leader of an evergreen
Colorado State advises against pruning the central leader of an evergreen, since the tree then grows several leaders that are easily damaged by wind and snow.
Topping instead of training
Purdue Extension points to research finding that a tree left to grow naturally, or one pruned well for structure, is sturdier than a topped tree, and notes that topping ends up costing the owner more.
Sources
- Structural Pruning of Young Shade Trees (CMG GardenNotes #613), Colorado State University Extension
- How to Prune Trees (NA-FR-01-95, revised 2012), USDA Forest Service, Northeastern Area State and Private Forestry
- Pruning Mature Shade Trees, Colorado State University Extension
- Corrective Pruning for Deciduous Trees (FNR-563-W), Purdue Extension, Forestry and Natural Resources
- Tree Owner’s Manual for the Northeastern and Midwestern United States (NA-FR-04-07), USDA Forest Service, Northeastern Area State and Private Forestry
- Northeast Community Tree Guide: Benefits, Costs, and Strategic Planting (PSW-GTR-202), USDA Forest Service, Pacific Southwest Research Station
- Pruning Evergreens (CMG GardenNotes #617), Colorado State University Extension
- What’s Wrong with Topping? (FNR-FAQ-14), Purdue Extension, Forestry and Natural Resources
Written in our own words from the public sources above, checked October 19, 2026. Arborist Practice Test is not affiliated with ISA.