Before You Pick Up a Saw — Understand What You're Working With
A tree is not a piece of furniture you reshape to your liking. It's a living organism that has spent years — sometimes decades — building its structure, root system, and internal plumbing. Every branch you remove is a wound. The tree will respond by compartmentalizing that wound, sealing it off, and growing around it. Your job as a pruner is to make cuts that the tree can heal from efficiently.
A good prune strengthens a tree. A bad prune can introduce disease, cause structural failure, and eventually kill something that took 50 years to grow. This guide is about doing it right.
— Information sourced from the Colorado State Forest Service and ISA (International Society of Arboriculture) guidelines.
When to Prune — Colorado's Seasons
Timing matters more than most people realize. The Colorado State Forest Service recommends late winter to early spring for most trees — just before new growth begins.
Late dormant season. Tree can clearly be seen. Wounds close fast as growth begins. Disease pressure is low.
Early dormancy. Tree has dropped leaves. Structure visible. Lower disease risk than mid-summer.
Summer pruning slows growth of specific branches. Fine for shaping and removing deadwood.
Active spring growth. Pruning now stresses the tree and wounds stay open longer during peak disease season.
The exception: Deadwood, broken branches, or anything hazardous can — and should — be removed any time of year. Never leave a dangerous branch waiting for the "right season."
The Most Important Thing: The Branch Collar
This single concept separates a good prune from a damaging one. The branch collar is where the branch connects to the trunk — and it contains the tree's healing tissue.
Where to Make the Cut
✅ Correct Cut
Just outside the branch collar. The slight bulge of bark where the branch meets the trunk is left intact. The tree heals cleanly around this point.
❌ Flush Cut
Cut flush with the trunk. Destroys the branch collar and the healing tissue inside it. The wound stays open, invites decay, and can hollow the trunk.
❌ Long Stub
Leaves a stub beyond the collar. The stub dies, decays inward, and creates a pathway for disease straight into the trunk. Never leave stubs.
The branch collar contains a ring of specialized cells that the tree uses to seal wounds. When you cut just outside it, those cells go to work immediately, rolling bark over the wound like a slow-motion zipper. Leave the collar intact and the tree heals. Destroy it and the wound never fully closes.
The 7 Principles of Good Tree Pruning
Have a reason before you cut
Never remove a living branch without a specific purpose. "It looks messy" isn't good enough. Valid reasons: removing deadwood, eliminating crossing/rubbing branches, raising canopy for clearance, improving structure, reducing wind resistance, or removing a hazard.
Protect the central leader
Most shade trees have one dominant central trunk — the leader. Never cut it. The leader determines the tree's height, structure, and long-term stability. If a tree has competing leaders (codominant stems forming a "V"), one can be gradually reduced while the tree is young — but never removed suddenly on a mature tree.
Space your scaffold branches
The permanent main branches (scaffold branches) should be evenly spaced up the trunk — both in vertical spacing and radially around the trunk. Branches that emerge too close together compete and create weak, included bark joints that can split catastrophically in storms.
Never remove more than 25% in one year
A tree's leaves are its food factory. Remove too many at once and you starve the tree, forcing it to draw on stored energy reserves. The Colorado State Forest Service and ISA both recommend removing no more than 25% of a tree's live crown in any single year. For stressed or recently transplanted trees, keep it under 10–15%.
Remove the 3 Ds first — Dead, Damaged, Diseased
Before doing any structural pruning, remove all dead, damaged, and diseased wood first. This can be done any time of year and is always the right first move. It also lets you see the tree's structure more clearly before making permanent decisions.
Never top a tree
Topping — cutting off the top of a tree to reduce height — is one of the most destructive things you can do to a tree. It destroys the natural form, creates dozens of large wounds that can't heal properly, triggers explosive weak regrowth ("water sprouts"), and eventually leads to structural failure or death. If height is a concern, consult a certified arborist about crown reduction or species replacement.
Go easy on young trees
Newly planted trees need their leaves to establish their root system. For the first 2–3 years after planting, only remove dead, broken, or truly hazardous branches. Let the tree build its energy reserves first. The structural pruning can wait until the tree is established.
Colorado Tree-Specific Pruning Guide
Different trees have different needs. Here's when and how to approach the most common trees in Denver metro yards.
Quaking Aspen
Late WinterPrune in late winter before leaf-out. Remove suckers regularly from the base — they'll take over if left unchecked. Never top. Aspens are short-lived (40–50 years) so structural pruning matters early.
Blue Spruce
Late WinterMinimal pruning needed — let it develop naturally. Remove dead interior branches and any crossing limbs. Never remove the central leader. Trim for clearance only when necessary.
Maple
Summer or FallMaples "bleed" sap heavily if pruned in late winter or spring. Prune in summer (July) or fall after leaves drop to avoid excessive sap flow. Otherwise standard collar-cut principles apply.
Crabapple
After BloomPrune immediately after spring bloom ends. Pruning in dormancy removes next year's flower buds. Remove crossing branches and water sprouts (upright shoots from major branches) aggressively.
Serviceberry
After BloomSame as crabapple — prune after spring bloom. Can be trained as multi-stem shrub or single-trunk tree. Remove suckers from base to maintain form.
Honeylocust
Late WinterCommon Denver street tree. Prune in late winter. Remove thorny water sprouts which emerge aggressively after pruning. Raise canopy gradually over years for clearance.
Cottonwood / Poplar
Late WinterFast-growing and brittle. Remove narrow-angle branch attachments early — they're failure points in Colorado's wind and snow. Never plant near power lines or structures.
Oak
Late Winter ONLYCritical: prune ONLY in late winter (Jan–March). Oak wilt disease spreads through pruning wounds in spring and summer. If you must prune outside dormancy, seal cuts immediately with pruning paint.
🚫 Never Do These — They Damage or Kill Trees
🌳 What Healthy Trees Are Worth to Your Property
The Right Tools
Sharp, clean tools make better cuts. A dull saw tears bark and creates ragged wounds that heal poorly.
Hand Pruners
For branches up to ¾". Bypass pruners make cleaner cuts than anvil types. Keep sharp.
Loppers
For branches ¾" to 1½". Long handles give leverage. Ratcheting types reduce hand fatigue.
Hand Saw (Folding)
For branches 1½" to 4". Curved blade cuts on the pull stroke. Incredibly useful tool.
Pole Saw
For reaching higher branches without a ladder. Manual is safer for a homeowner. Keep it sharp.
Isopropyl Alcohol
Disinfect tools between trees (and between cuts on diseased wood). 70% concentration works well.
Safety Gear
Eye protection, work gloves, hard hat if working under a canopy. Non-negotiable.
When to Call a Certified Arborist
There are things you can do yourself — and things you shouldn't. Know the difference.
- Call an ISA Certified Arborist when: Any branch over your roof, near power lines, or requiring a chainsaw above shoulder height
- Call when: The tree shows signs of disease, decay, or structural damage you're not sure about
- Call when: The tree is large, mature, and close to your house or structures
- Call when: You're not 100% certain what you're doing
A tree that took 40 years to grow can be destroyed by one bad cut or one bad contractor. Find ISA Certified Arborists in Colorado at isa-arbor.com.
Sources & Credit: Pruning guidance on this page is based on recommendations from the Colorado State Forest Service (CSFS) at Colorado State University, and the International Society of Arboriculture (ISA). For the most authoritative Colorado tree care guidance, visit the CSFS website or consult an ISA Certified Arborist. Trees are too important — and too valuable — to wing it.
🎬 Watch: How to Prune Trees — Done Right
📚 Authoritative Resources
Colorado State Forest Service — Tree Care GuideThe authoritative Colorado source for tree pruning and care ISA — Find a Certified Arborist Near YouHire someone qualified. Your tree's life may depend on it. ISA Rocky Mountain ChapterLocal chapter of the International Society of Arboriculture📖 Want to Learn More? — Tree Science & Arboriculture Research
🌱 More Colorado Homeowner Guides
🌳 Best Trees for Colorado Yards → 📅 Colorado Planting Calendar → 💧 Sprinkler Startup Guide → ❄️ Spring AC Startup →A Beautiful Yard Starts With Healthy Trees.
Mature trees are one of the biggest value-adds a Colorado property can have. When you're thinking about what your home is worth — let's talk.
Get a Free Home Valuation →