Tree Care and Maintenance
Seasonal Tree Care Tips: Fall
Common Tree Root Myths
When we look around our neighborhoods, we tend to focus on what is visible: the vibrant autumn leaves, the soaring branches, and the cooling shade. But the most critical part of our city’s urban canopy is almost entirely hidden from view. Roots!
Unfortunately, what we think we know about what happens underground is often wrong. Long-held misconceptions about tree roots cause well-meaning homeowners to inadvertently damage their property, waste money on improper care, and weaken trees ahead of winter storms. By debunking these five common tree root myths, we can better protect our private landscapes and preserve our shared community forest.
Myth #1. The Mirror Image Myth
The Misconception: Roots grow as deep as the tree is tall.
The Reality: Tree roots are generally located within the top 12 to 24 inches of soil. Roots grow shallow where water and oxygen are available. Roots require oxygen to survive, which is only found in high concentrations near the soil surface. Because roots sit right beneath the grass line, everyday activities like parking vehicles on lawns or changing soil grades can easily suffocate and stress or kill a tree.
Myth #2. The Deep Taproot Myth
The Misconception: It is widely believed that large trees stay upright during heavy windstorms because a massive, carrot-like taproot plunges straight down into the earth's core.
The Reality: While many tree seedlings grow a temporary taproot to establish themselves, almost all mature trees completely lose their taproot as they age. Deep underground soil layers are highly compacted and lack the oxygen required for root survival. Instead of anchoring themselves vertically, mature trees maintain their stability through a vast, interlocking web of horizontal lateral roots. These horizontal roots act like guy-wires on a tent. When strong winter winds blow, the tree relies on the collective weight of the soil sitting on top of its wide surface root plate to stay upright.
Myth #3. Roots Stop at the "Dripline"
The Misconception: The dripline is the outermost ring of a tree’s overhead canopy. A common myth dictates that once you step past the leaves, you are safely out of the tree's root zone.
The Reality: While the majority of roots are generally within the dripline area, often defined as the critical root zone, a mature tree’s root system can extend two to three times the radius of its canopy if there is available growing space. If a tree's branches extend 15 feet out from the trunk, its large structural and fine absorbing roots could reach 30 to 45 feet away as long as there is water, oxygen, and nutrients. This is why site disturbance far outside the dripline can still result in stress or injury.
Myth #4. Roots Actively Seek and Destroy Foundations and Pipes
The Misconception: Homeowners often blame aggressive tree roots for cracking solid concrete foundations and breaking open sewer and water pipes.
The Reality: Tree roots are opportunistic, not destructive invaders. They lack the mechanical ability to pierce sound crack-free concrete or properly functioning pipes. Roots simply follow the path of least resistance in search of water and oxygen. If a house foundation settles and develops a structural crack, or if an old clay sewer pipe begins to leak, moisture escapes into the surrounding soil. Tree roots find this moisture trail and will grow into existing cracks or defective joints in pipes. Over time, the roots grow thicker and will expand the initial crack and contribute to the damage, but they never started it.
Myth #5. Deep-Root Injections are the Best Way to Water
The Misconception: To properly hydrate a tree, water must be forced deep underground using high-pressure probes or deep injection watering systems.
The Reality: Because the delicate, hair-like absorbing roots—the ones actually responsible for absorbing water—live in the top foot of soil, deep injections push water completely past the target zone. The healthiest, most efficient way to deep water any tree is a slow, surface-level soak using a soaker hose or a trickling hose moved across the entire root zone.
Understanding root biology changes how we manage our properties. This autumn, as you prepare your yard for the coming winter, keep these subterranean realities in mind.
Learn more about what’s really going on underground and other common misconceptions about trees by visiting these resources:
- Uncovering the Truth About Tree Roots
- 10 Tree Myths to Think About
- Landscape Tree Care Myths and Facts
- Proper Ways to Water Your Trees
Please check back for more seasonal tree care and maintenance advice!
Link to Tree Care and Maintenance Archives
Archives
Summer 2026: Five Common Tree Care Mistakes (and Easy Ways to Avoid Them)
Spring 2026: Protecting Your Trees: Why Lawn Equipment Causes Damage and How to Prevent It
Winter 2026: Start Smart: What to Consider Before Planting a New Tree
Summer 2025: Heat Stress and Sunscald
Spring 2025: Trees for Bees…and Other Pollinators, Too
Winter 2025: Fruit Tree Maintenance
Fall 2024: For a Healthier Yard, Leave the Leaves
Summer 2024: Tree Risk Assessment
Spring 2024: Invasive Ivy Removal
Winter 2024: Clean and Sharp Pruners
Fall 2023: Mediterranean Oak Borer
Summer 2023: Supplemental Watering and Mulch to Prevent Drought Stress in Trees
Winter 2023: Pruning: Standards and Best Practices
Summer/Fall 2022: Emerald Ash Borer
Winter/Spring 2022: Nesting Season
Fall 2021: Healthy Trees are Defended Trees
Special Edition: After the Storm
Winter 2021: What is an Arborist?
Summer 2020: Retaining and Creating Snags for Wildlife
Spring 2020: Mulch: Numerous Benefits and Easy Application
Winter 2020: Tree Planting: To Stake or Not to Stake?
Fall 2019: Insects and Diseases
Summer 2019: Drought Stress Revisited
Spring 2019: Trees and Construction
Summer 2018: Emerald Ash Borer
Spring 2018: Pruning Young Trees
Winter 2018: Tree Related Storm Damage
Fall 2017: New Tree Selection and Planting
Summer 2017: Trees and Turfgrasses
Spring 2017: English Ivy Removal
Winter 2017: Recognizing Tree Risk
Fall 2016: Preparing Trees for Winter
Additional Tree Care Resources:
| National Arbor Day Foundation | The Morton Arboretum |
| Oregon Department of Forestry | Tree Care Info |
| ISA Find an Arborist | Alliance for Community Trees |
| Oregon Department of Forestry |
Right Tree in the Right Place
Use this handy guide for assistance in choosing the right species of tree based on the constraints of a site, such as overhead wires, narrow plant strips, and proximity to structures.
"Right Tree Right Place" - helpful information such as "Use this guide for assistance in choosing the right species of tree based on the constraints of a site, such as overhead wires, narrow plant strips, and proximity to structures."
"Master Plant List" - a guide to the plants that are acceptable for mitigation requirements in Lake Oswego.
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