Building Healthy Soil Around Mature Trees
How thoughtful soil management can improve and protect the growing environment supporting your trees.
Why This Matters
Mature trees are long-lived organisms supported by extensive root systems and complex soil environments. While leaves, branches, and trunks are the most visible parts of a tree, many of the processes that influence long-term health occur below ground.
Healthy soil provides more than nutrients. It stores and moves water, contains pore spaces that allow oxygen to reach roots, supports beneficial biological activity, contributes organic matter, and provides the physical environment through which roots grow.
In residential and urban landscapes, soil conditions are often very different from those found in an undisturbed forest. Construction, grading, lawn establishment, vehicle and foot traffic, changes in drainage, removal of natural organic matter, and years of landscape maintenance may gradually alter the soil environment.
Supporting a mature tree therefore involves more than responding to visible symptoms. Protecting and improving the environment surrounding its roots may help preserve tree health, resilience, and function for years to come.
Mature Trees Depend on a Broad Root Zone
A mature tree’s root system extends far beyond the base of the trunk. Although root growth varies with tree species, soil conditions, moisture, available oxygen, and physical barriers, roots can extend beyond the edge of the canopy.
Many actively absorbing roots are located relatively close to the soil surface, where oxygen, moisture, organic matter, and biological activity are generally more available.
This means activities occurring throughout the surrounding landscape may influence the tree—even when they do not take place immediately beside the trunk.
Changes that may affect the root zone include:
Construction or excavation
Trenching for utilities
New driveways, sidewalks, patios, or retaining walls
Changes in soil grade
Repeated vehicle or equipment traffic
Heavy foot traffic
Soil compaction
Changes in drainage
Prolonged flooding or standing water
Removal of nearby trees or vegetation
Repeated disturbance from lawn or landscape work
Storage of soil, stone, equipment, or building materials beneath the canopy
Because much of the root system is hidden from view, root injury and declining soil conditions may not be immediately apparent. A mature tree may continue to appear relatively normal for months or years while gradually losing vigor
What Makes a Healthy Soil Environment?
Healthy soil is sometimes discussed primarily in terms of fertilizer or nutrient levels. Nutrients are important, but they are only one part of a much larger and more complex system.
A supportive soil environment generally includes an appropriate balance of:
Mineral soil particles
Pore space
Oxygen
Moisture
Organic matter
Available nutrients
Beneficial biological activity
Suitable soil structure
Adequate rooting volume
The spaces between soil particles are especially important because they allow air and water to move through the soil. When soil contains an appropriate balance of moisture and oxygen, roots are better able to grow and function.
Soil compaction occurs when soil particles are pressed closer together, reducing these pore spaces. Compaction may result from construction activity, heavy equipment, repeated vehicle or foot traffic, parking beneath trees, or working soil while it is wet.
As compaction increases, water may run across the surface rather than soak into the ground, oxygen movement may decline, and roots may have greater difficulty expanding through the soil. Over time, these changes may contribute to reduced root growth, declining biological activity, limited nutrient availability, and increased environmental stress.
Healthy roots also require an appropriate balance of moisture and oxygen. Excessively dry soil may limit water availability and contribute to drought stress, while soil that remains saturated for extended periods may contain less oxygen and interfere with healthy root function.
Organic matter contributes to this broader soil system by supporting biological activity, nutrient cycling, soil aggregation, moisture retention, and soil structure. In a forest, leaves, small branches, bark, and other plant material naturally accumulate and decompose. In maintained landscapes, these materials are often removed, reducing the natural return of organic matter to the soil.
A soil may contain adequate nutrients and still be a difficult environment for root growth. Adding fertilizer alone will not correct problems caused by compaction, poor drainage, restricted rooting space, excessive soil moisture, or physical root damage.
Healthy soil is not defined by any one measurement or product. It develops through the interaction of physical, chemical, and biological processes that together create an environment capable of supporting healthy root growth.
UFT INSIGHT
Healthy soil is more than fertile soil. Long-term tree health depends on the interaction of soil structure, pore space, oxygen, moisture, organic matter, biological activity, nutrients, and adequate rooting space.
Protect the Root Zone and Root Flare From Additional Disturbance
Protecting the root zone from additional disturbance is often one of the most valuable steps in supporting a mature tree.
Whenever practical:
Keep vehicles and heavy equipment away from the root zone
Avoid repeatedly parking beneath mature trees
Limit unnecessary foot traffic over compacted or exposed soil
Do not store soil, stone, equipment, or construction materials beneath tree canopies
Avoid trenching through major portions of the root system
Protect trees and root zones before construction begins
Minimize unnecessary changes in soil grade
Avoid repeatedly disturbing the soil beneath mature trees
Use designated access routes during construction or landscape work
Maintain adequate space around important trees
Tree-protection planning is generally most effective before construction or site disturbance begins.
Once roots have been severed or soil has been heavily compacted, restoring the original growing environment may be difficult. Preventing damage is often more effective than attempting to correct it after symptoms appear.
The root flare—sometimes called the trunk flare—is the transition where the trunk widens and meets the major structural roots.
On many trees, this area should be visible at or near the soil surface.
Potential concerns include:
A trunk that enters the ground like a straight pole
Soil piled against the trunk
Mulch covering the root flare
Excessive planting depth
Changes in soil grade
Girdling or circling roots
Bark that remains buried or continuously moist
Decay or fungal growth near the base
A buried root flare may conceal important structural roots and create conditions that affect bark, root development, and long-term tree health.
Correcting a buried root flare should be approached carefully. Removing soil without understanding root location may damage fine or structural roots.
When concerns are present, root-flare evaluation or careful air excavation may help identify existing conditions and guide appropriate management.
Air Spading May Help Evaluate Certain Soil and Root Conditions
Air excavation uses compressed air to carefully move soil while reducing the likelihood of cutting or tearing woody roots.
Depending on the tree and site, air-spade work may be used to:
Expose a buried root flare
Evaluate root depth
Identify girdling or circling roots
Examine suspected root damage
Investigate changes in soil grade
Remove excess soil from around the trunk
Evaluate soil structure and compaction
Support certain root-zone improvement practices
Air spading is not necessary for every tree, and it does not automatically correct all soil problems.
The purpose and extent of the work should be based on the tree, site conditions, suspected concerns, and management objectives.
For more information, see: Air Spading: What It Is and Why We Use It.
Mulch Can Help Recreate Some Forest-Floor Conditions
An appropriate layer of organic mulch may help support the soil environment around mature trees.
Potential benefits include:
Moderating soil temperature
Reducing moisture loss from the soil surface
Limiting competition from turfgrass
Protecting soil from erosion and surface disturbance
Reducing the risk of mower and string-trimmer damage
Gradually contributing organic matter as the mulch decomposes
Supporting biological activity near the soil surface
Whenever possible, mulch should be spread broadly rather than piled deeply.
A broad, moderate mulch layer generally provides greater root-zone benefit than a small mound concentrated around the trunk.
Mulch should not be piled against the bark or used to bury the root flare. Excessive mulch may retain moisture against the trunk, conceal developing problems, and encourage roots to grow into the mulch layer.
The goal is to protect and support the soil—not to create a mound around the tree.
For more information, see: Mulching Done Right.
Turfgrass and Trees Compete for Resources
Trees and turfgrass often occupy the same landscape, but they have different management needs.
Dense turf may compete with tree roots for:
Water
Nutrients
Rooting space
Access to the upper soil environment
Maintaining turf directly against the trunk also increases the likelihood of damage from mowers and string trimmers.
Expanding a mulch area around a mature tree may help reduce competition while protecting the soil surface and separating the trunk from lawn equipment.
When converting turf to mulch:
Avoid cutting deeply into the soil
Do not use equipment that may damage surface roots
Avoid piling removed soil over nearby roots
Do not bury the root flare
Expand the mulch area gradually when needed
Keep mulch away from direct contact with the trunk
The mulch area does not need to end at the edge of the canopy. In many landscapes, the greatest practical benefit comes from creating the broadest appropriate mulched area the site can reasonably accommodate.
Understand the Soil Before Treating the Tree
A mature tree that appears stressed does not automatically need fertilizer.
Yellow leaves, reduced growth, canopy thinning, premature fall color, or branch dieback may be associated with:
Drought
Excessive soil moisture
Root damage
Soil compaction
Poor drainage
Restricted rooting space
Construction disturbance
Insects
Disease
Nutrient availability
Other environmental stresses
Applying nutrients without understanding the underlying cause may not address the actual problem. In some situations, encouraging additional aboveground growth while the root system is under stress may be counterproductive.
Before selecting a treatment, consider:
The tree species, age, and condition
Existing growth and canopy density
Soil structure and compaction
Moisture and drainage
Available rooting space
Site history
Recent construction or landscape changes
Known or suspected nutrient limitations
The purpose of the proposed treatment
Soil testing may provide useful information about pH, organic-matter content, available nutrients, nutrient imbalances, soluble salts, soil texture, and other soil characteristics.
However, laboratory results do not tell the entire story. A standard soil test may not identify compaction, restricted rooting space, root damage, poor drainage, changes in soil grade, excessive planting depth, or problems at the root flare.
Soil-test results are most useful when considered together with the condition of the tree, its root zone, drainage, soil profile, site history, and visible symptoms.
Testing should help answer a management question—not simply produce numbers.
The goal should not be to stimulate growth or add nutrients without a clear purpose. The goal should be to identify conditions that may be limiting the tree and select management practices that support both the tree and its growing environment.
Supporting the Soil With Organic Matter and Carefully Selected Amendments
Depending on the tree and existing soil conditions, carefully selected amendments may be used to support soil structure, moisture retention, nutrient cycling, organic-matter content, and beneficial biological activity.
Potential soil-supporting materials may include:
Organic matter
Compost-derived materials
Biochar
Humates
Beneficial biological components
Carefully selected nutrients
Biochar is a stable, carbon-rich material that may contribute to soil structure, moisture retention, nutrient-holding capacity, and habitat for beneficial soil organisms.
Humates are derived from decomposed organic materials and contain humic substances that may influence nutrient availability, soil aggregation, and biological processes.
However, no single amendment is appropriate for every tree or every soil.
The potential benefit of an amendment depends on:
Existing soil conditions
Soil texture and structure
Moisture and drainage
Existing organic matter
Tree species, age, and condition
Root-zone limitations
Application method and rate
Long-term management goals
Soil amendments should not be viewed as instant solutions or substitutes for appropriate watering, drainage, mulching, root-zone protection, or correction of significant soil problems.
The purpose of soil improvement is not to apply as many products as possible. It is to understand the existing soil environment, identify limiting conditions, and use appropriate practices to support long-term root function.
UFT’s Soil-Focused Approach to Deep Root Feeding
The term Deep Root Feeding is often associated primarily with injecting fertilizer into the soil. UFT takes a broader, soil-focused approach.
When appropriate for the tree and site, UFT’s Deep Root Feeding program is designed to support soil health and improve the root-zone environment rather than simply stimulate rapid aboveground growth.
The treatment uses a carefully selected blend that includes organic matter, biochar, humates, beneficial biological components, and nutrients intended to support:
Soil structure and function
Moisture and nutrient retention
Beneficial biological activity
Nutrient cycling
Root-zone health
Long-term tree resilience
Applying the treatment below the soil surface distributes the soil-supporting blend throughout portions of the root zone while creating localized channels that may help improve the movement of air and water.
Deep Root Feeding does not replace appropriate watering, proper mulching, root-zone protection, or correction of significant drainage and compaction problems. It is one potential component of a broader, long-term soil- and tree-management strategy.
The appropriate treatment depends on the tree, soil conditions, existing moisture, drainage, root-zone limitations, and management goals.
Avoid Aggressive Soil Disturbance Around Mature Trees
Improving soil does not necessarily mean digging, tilling, or replacing it.
Mature trees may have large numbers of fine absorbing roots near the soil surface. Aggressive cultivation may damage those roots and create additional stress.
Avoid:
Deep tilling beneath the canopy
Rototilling around mature trees
Cutting roots to install landscape beds
Excavating without understanding root location
Mixing amendments deeply into established root zones
Adding large amounts of soil over existing roots
Repeatedly disturbing surface roots
Soil-management practices should improve the growing environment while minimizing damage to the root system already occupying the site.
In many situations, gradual surface-based improvements, broad organic mulch, root-zone protection, and carefully selected treatments may be more appropriate than aggressive soil disturbance.
What Property Owners Can Do
Practical ways to support soil health around mature trees include:
Protect the root zone from vehicles and heavy equipment
Avoid repeatedly parking beneath trees
Limit unnecessary soil disturbance
Maintain a broad, appropriate layer of organic mulch
Keep mulch away from direct contact with the trunk
Preserve a visible root flare
Reduce turf competition when practical
Monitor soil moisture during prolonged dry periods
Check soil conditions before increasing irrigation
Avoid keeping the root zone continuously saturated
Protect trees before construction begins
Avoid unnecessary changes in soil grade
Do not store heavy materials beneath tree canopies
Avoid automatically applying fertilizer when symptoms appear
Use soil testing when it can help answer a specific management question
Select soil amendments based on existing conditions and identified goals
Monitor changes in canopy density, annual growth, leaf size, and overall tree condition
Supporting soil health is generally a long-term process. Small, thoughtful improvements may be more beneficial than aggressive short-term changes.
When Professional Evaluation Is Useful
A professional soil and tree evaluation may be appropriate when:
Canopy thinning or branch dieback continues to increase
Annual growth appears reduced
Leaves are smaller, pale, scorched, or prematurely changing color
Soil is visibly compacted
Water runs off rather than soaking into the ground
Water remains near the tree for extended periods
Construction, grading, trenching, or excavation has occurred
The root flare is buried or difficult to locate
Soil or mulch has been added around the trunk
Girdling roots are visible or suspected
A mature tree is growing in a restricted landscape area
A soil amendment or treatment is being considered without a clear objective
The tree has significant landscape, environmental, historical, or personal value
An arborist can evaluate the tree together with its growing environment and consider soil conditions, drainage, root-zone limitations, site history, tree species, visible symptoms, and long-term management goals.
A Long-Term Approach to Soil and Tree Health
Healthy soil is not created by a single application, and mature-tree health is rarely determined by one factor.
The soil environment changes over time as organic matter decomposes, roots grow, water moves, biological processes occur, and the surrounding landscape is altered.
A mature tree may experience drought, construction activity, soil compaction, drainage changes, root injury, insects, disease, and other stresses at different points throughout its life. These factors may interact and gradually influence the tree’s ability to respond to future challenges.
Supporting long-term tree health begins with understanding the soil, protecting the root system, maintaining appropriate moisture, reducing avoidable disturbance, and selecting management practices based on actual site conditions.
The goal is not simply to make a tree grow faster.
The goal is to create and protect a soil environment that allows the tree to function, adapt, and remain resilient for years to come.
Sources & Further Reading
This article reflects established arboricultural principles and professional field experience. For additional information, explore educational resources from:
International Society of Arboriculture — Tree Owner Resources
Michigan State University Extension — Trees and Forests
University of Minnesota Extension — Trees and Shrubs
Cornell University — Urban Horticulture Institute
HEALTHY SOIL. | STRONGER TREES. | LASTING LANDSCAPES.
Interested in improving the growing environment around one of your trees? UFT Tree Care Specialists provides science-based tree diagnostics, soil evaluation, consulting, Deep Root Feeding, root-flare evaluation, and plant health care throughout Northern Michigan.
ufttree.care • ben@ufttree.care • 231-409-0442
