How Do Trees Survive in Winter?

How trees survive freezing temperatures (with practical notes on winter pruning). Tree biology, winter tree care, frost damage, cold hardiness, and seasonal pruning explained

Trees are made up of nearly 50% water. So in the dead of winter — when temperatures drop deep below freezing — a logical question arises: why don’t trees freeze and burst like water pipes?

The truth is, parts of trees do freeze in winter. If you’ve ever walked through a quiet forest on a cold day and heard sudden popping or cracking sounds, that’s often the sound of freezing wood fibers and internal pressure changes inside the tree. But unlike pipes, this process is usually not fatal and rarely causes serious structural damage.

Why Trees Don’t Die When They Freeze

For a tree to survive winter, it doesn’t need to protect every part of its structure — it only needs to protect its living cells. Much of what we think of as “wood” in a tree is actually made up of dead structural tissue, which can freeze without killing the tree. This natural biological design is one of the core reasons trees can survive extreme cold, frost events, deep freezes, and long winter periods.

In simple terms, a tree is built with a clear functional separation between living tissue and structural support tissue. Only a small portion of the tree’s internal structure is biologically active and vulnerable to freezing damage. The rest exists mainly to provide strength, transport pathways, and mechanical stability — and can tolerate freezing temperatures without causing fatal injury.

What trees actually protect in winter:

• Living cells in the cambium layer – the growth tissue responsible for new wood and bark formation

• Active transport tissues that must remain functional for spring recovery

• Buds and meristematic tissue, which contain next season’s leaves, flowers, and growth points

• Energy storage cells, where sugars and carbohydrates are stored for winter survival

• Cell membranes and internal fluids, which are protected through dehydration and antifreeze-like compounds

Everything else — much of the trunk, large portions of branches, and internal support structures — can freeze safely without killing the tree. These parts are designed to act as biological insulation and structural buffering, protecting the sensitive living tissues deeper inside.

This layered survival system allows trees to endure repeated freeze–thaw cycles, temperature swings, and prolonged subzero conditions without catastrophic damage. Instead of preventing freezing entirely, trees manage where freezing can happen safely, and where it must be biologically controlled — a strategy that is far more efficient than trying to keep the entire organism warm.

Xylem and Phloem: The Tree’s Internal Transport System

Inside every tree are two key water-transport systems: xylem and phloem. Xylem moves water and nutrients from the roots to the canopy, while phloem transports sugars and energy produced through photosynthesis back down through the tree. These systems are made up of thousands of microscopic tubes. If some of them freeze and rupture, the tree simply reroutes flow through others — a built-in biological redundancy system that prevents total failure.

Flexibility, Cold Hardiness, and Structural Resilience

Unlike rigid steel pipes, tree tissues are also flexible, allowing them to expand slightly before rupturing. This elasticity, combined with cellular dehydration and seasonal dormancy processes, gives trees their natural cold hardiness and resistance to winter damage.

Seasonal Adaptation and Winter Survival Strategies

But freezing tolerance alone isn’t enough. Since trees don’t generate heat like animals, they rely on seasonal biological adaptation. As summer shifts into fall, trees begin active winter preparation. Deciduous trees drop their leaves to conserve energy and water, while conifers like pines, spruces, and firs use needle structures, resin systems, and antifreeze-like cellular chemistry to survive extreme cold.

What This Means for Winter Pruning and Tree Care

Understanding these natural survival systems is essential for proper winter pruning, long-term tree health management, frost damage prevention, and structural stability — especially for arborists, landscapers, and property managers working in cold climates.

Winter is not just a “safe” season for pruning — it’s a biologically strategic window. During dormancy, trees redirect energy inward, metabolic activity slows, and vulnerability to infection and pest pressure is significantly reduced. This makes the dormant season ideal for structural correction, risk mitigation, and long-term canopy planning.

At the same time, cold weather changes how trees respond to stress, wounds, and mechanical damage. Understanding winter physiology helps prevent unnecessary injury and ensures that pruning work supports recovery rather than weakening the tree before spring growth.

Practical implications for winter tree care and pruning:

• Dormant-season pruning reduces biological stress. Cuts made during dormancy cause less physiological shock and allow the tree to allocate energy toward healing when growth resumes in spring.

• Lower disease and pest transmission. Many pathogens and insects are inactive in cold temperatures, reducing the risk of infection through fresh pruning wounds.

• Improved structural visibility. Leaf-off conditions make it easier to identify crossing limbs, weak unions, deadwood, and structural defects.

• Better long-term growth control
  Winter pruning influences spring growth direction, crown structure, and load distribution.

• Safer working conditions. Frozen ground reduces soil compaction, root zone disturbance, and turf damage during equipment use.

• More accurate risk management. Deadwood, frost cracks, and structural failures are easier to assess when foliage is absent.

• Health-focused pruning instead of reactive cutting. Winter allows for proactive tree care planning instead of emergency-based interventions.

• Better outcomes for young trees. Structural training pruning in winter sets proper form and reduces future correction needs.

Biological Antifreeze: How Trees Prevent Internal Freezing

Their strategy is to turn the water that flows inside them into a form of biological antifreeze. This process works similarly to how salt melts ice on sidewalks — dissolved molecules lower the freezing point of water.

In trees, instead of salt, this role is played by sugars produced through photosynthesis. High concentrations of sugars and minerals change the chemical structure of internal fluids, thickening them into tree sap and lowering their freezing temperature.

Many trees actively increase this concentration during fall and early winter by:

• Producing and storing more sugars

• Releasing excess water from cells

• Allowing controlled dehydration in tissues

• Concentrating minerals and dissolved compounds

This process transforms normal water into a freeze-resistant biological fluid, protecting living cells from ice crystal formation and internal rupture.

Sap Chemistry and Seasonal Sugar Concentration

Some species, especially birches and maples, use a less extreme form of this antifreeze strategy combined with leaf shedding during winter dormancy. By shedding their leaves, these trees reduce water loss and minimize the risk of ice formation within fragile tissues. The combination of sugar-rich sap and leaf drop helps protect their living cells from freezing damage while still conserving energy. This strategy allows them to survive harsh winter temperatures while maintaining the ability to resume growth quickly in spring.

Sugar-Rich Sap in Maples and Birches

In these species, sap becomes noticeably sweeter in winter. This sugar-rich sap is what gets boiled down to produce maple syrup, primarily from Acer saccharum (Sugar Maple).

This seasonal sugar concentration:

• Lowers freezing temperature – The higher sugar levels in sap prevent ice from forming inside cells, reducing freeze damage.

• Protects living cells – Sugar-rich sap acts as a natural antifreeze, keeping vital tissues alive during winter.

• Supports dormancy survival – Concentrated sugars help the tree maintain essential functions while in a dormant state.

• Provides stored energy for spring growth – Sugars accumulated in winter supply the energy needed for new shoots, leaves, and flowers in spring.

Tree Dormancy: A Biological Survival Mode

During winter months, both deciduous trees and evergreens enter a dormant state similar to hibernation in animals. During this period, growth stops completely, and metabolic processes slow down dramatically to conserve energy. Photosynthesis ceases or drops to minimal levels, and the tree survives using stored carbohydrates and nutrients accumulated during the growing season. Dormancy also helps trees withstand extreme cold, frost events, and repeated freeze-thaw cycles without sustaining permanent damage. This biological survival mode is essential for maintaining long-term health and ensuring a strong, vigorous restart when spring arrives.

What Happens During Dormancy

• Growth processes stop – The tree temporarily halts new shoots, leaves, and branch expansion to conserve energy.

• Photosynthesis shuts down – With little sunlight and low temperatures, the tree stops producing energy from light.

• Energy production pauses – Cellular activity decreases, and the tree relies on previously stored energy reserves.

• Metabolism slows dramatically – All biochemical processes slow, reducing resource consumption during winter.

• Trees survive on stored carbohydrates and nutrients – Energy saved from the growing season sustains vital tissues until spring growth resumes.

This dormant state allows trees to endure long periods of cold using internal energy reserves while minimizing biological activity and water movement.

Winter Pruning and Dormant-Season Growth Response

Winter is an ideal season to prune many tree species. Pruning during dormancy invigorates trees and promotes faster, healthier regrowth in spring. Because metabolic activity is low, trees experience less physiological shock from pruning cuts. Energy reserves remain protected in the root system and trunk, allowing for strong recovery once growth resumes. This creates a healthier balance between structural correction and biological resilience.

Why Dormant-Season Pruning Works

1. Remaining branches receive more water and nutrients – The tree channels resources to the healthiest branches, promoting stronger growth.

2. Energy resources are redirected into fewer growth points – Pruning focuses the tree’s energy on key areas for optimal development.

3. Structural development improves – Branches grow in a balanced, stable structure, reducing weak or crossing limbs.

4. Stress response is lower – Dormant pruning minimizes biological stress and helps the tree maintain vitality.

5. Recovery is faster in spring – The tree regrows quickly once growth resumes, supporting robust spring development.

6. Disease and pest transmission risk is reduced – Dormant-season pruning lowers the chance of infections and infestations.

This combination creates a highly efficient recovery environment for the tree. Growth responses become more controlled, predictable, and structurally balanced. Instead of chaotic regrowth, trees develop stronger frameworks, better load distribution, and healthier long-term canopy structure.

Exceptions to Winter Pruning

There are important seasonal exceptions, especially in early spring. As trees begin to exit dormancy, internal sap pressure increases and biological activity accelerates. Pruning during this transition period can trigger excessive sap flow, stress responses, and slower wound closure. Timing becomes critical, not because of tree health risks, but because of management challenges, cleanup issues, and client experience concerns.

Sap-Bleeding Species

Some species, particularly maples, birches, and elms, can bleed large amounts of sap if pruned too close to spring. This happens due to rising internal sap pressure as trees exit dormancy and prepare for active growth. While this sap flow looks dramatic, it is biologically normal and does not indicate damage or health decline in the tree.

However, from a management and maintenance perspective, sap bleeding creates several practical issues for tree care professionals and property owners.

While biologically harmless, sap bleeding can cause practical management issues, making timing important for professional tree care and property maintenance.

FAQ