Trees Don’t “Heal,” They “Seal”
When you beloved tree gets a nasty wound or gash on a tree trunk, your first instinct might be to grab a sealant, slap on a homemade paste, or try some quick DIY fix. But here’s the truth: trees don’t heal the way human skin does. They compartmentalize, isolate, and wall off damage using an internal process called CODIT (Compartmentalization of Decay in Trees).
This means of dealing with physical trauma or attacking pests/pathogens allows your tree (s) to grow for decades, centuries and for some, even millennia. This ability is built in to the very genetics of your tree, making it the ultimate survivor … Your job as a tree owner/caregiver isn’t to “fix” the wound but to help the tree do its job better — supporting its natural defenses instead of working against them.
Let’s break down what actually works — based on research, not backyard myths.
How Trees Really Heal: CODIT Explained
Instead of repairing damaged tissues like animals, trees build walls inside to surround the injury. Dr. Alex Shigo, often called the “father of modern arboriculture,” first mapped this system in the 1970s. CODIT describes how trees form four distinct types of walls to block decay and protect living tissue:
- Wall 1: Resists vertical spread – up & down
- Wall 2: Resists inward spread – toward the middle of the trunk or branch (pith)
- Wall 3: Resists lateral spread – around the trunk from where the damage occurs
- Wall 4 (the strongest): Forms new wood to seal off the area – this is the wound closure that you see long after a pruning wound has been done properly
This system slows or stops decay but doesn’t reverse the damage. That’s why proper care before and after an injury matters — you can’t undo a bad cut or damage to the root, but you can help the tree wall it off more effectively.
(For deeper reading: Shigo, A.L., & Marx, H.G. (1977). Compartmentalization of Decay in Trees. USDA Forest Service.)
Evidence-Based Strategies for Managing Tree Wounds
✅ 1. Clean, Proper Pruning Cuts
Research consistently shows that the quality of the cut determines how well a tree can compartmentalize.
- Avoid flush cuts; always leave the branch collar intact.
- Make smooth, clean cuts (no ragged edges).
- Sterilize pruning tools, especially when disease is present.
(Reference: International Society of Arboriculture, Best Management Practices: Tree Pruning.)
✅ 2. Skip the Wound Dressings (Mostly)
Multiple studies, including from the USDA Forest Service, show that most dressings (tar, latex paint, asphalt sealers) don’t prevent decay and may trap moisture, making things worse.
- Exception: In oak wilt zones, immediately seal wounds to block beetle transmission.
(Reference: Appel, D.N. (2001). The Role of Wound Dressings in Oak Wilt Management.)
✅ 3. Reduce Environmental Stress
A strong, healthy tree can close wounds faster. Help it out by:
- Applying 2–4 inches of organic mulch (keep it off the trunk!).
- Maintaining proper soil moisture, especially in drought.
- Avoiding soil compaction over the root zone.
✅ 4. Prevent Sunscald on Exposed Wood
After storm damage or heavy pruning, thin-barked trees like maples and young oaks can get sunscald (bark splitting from sun stress).
- Use commercial tree wraps in high-risk seasons.
- Apply diluted white latex paint (1:1 with water) to reflect sunlight.
✅ 5. Explore Biological Aids (With Caution)
Emerging research suggests some beneficial microbes, like Trichoderma species, may help suppress wood decay fungi. Products like RootShield show promise, but they’re not yet standard practice and should be used thoughtfully. I’ve been very impressed with my own personal and professional experimentation with a bacterial antifungal Product from Microlife Fertilizers from their Microgrow Liquid Antifungal (AF)
✅ 6. Focus on Soil Health
Rather than attacking the wound directly, support the tree systemically:
- Apply compost or microbial inoculants to the root zone.
- Add biochar or humic substances to improve soil structure and microbial activity, especially
🚨 What to Avoid
- Don’t paste on thick, wet mixtures that block airflow.
- Don’t wrap wounds in plastic or non-breathable materials — you’ll trap in moisture and create decay conditions.
- Don’t fill in cavities with any type of foam filler.
🌟 Final Takeaway
Wounds are part of a tree’s life. God in His infinite wisdom has equipped trees with incredible internal defenses that work better when we stay out of the way. Your role as a caretaker isn’t to seal wounds shut like a Band-Aid but to reduce stress and let the tree’s biology do the work.
Save the homemade brews for the garden experiments — when it comes to trees, stick to science-backed methods for long-term success.
If you want a professional assessment or custom care plan for your tree, book a digital consultation today at 👉 www.arboristondemand.com. Let’s keep those trees thriving for generations to come! 🌳💚
My Best,
Matt Latham
ISA Board Certified Master Arborist #TX-3737B
ASCA Registered Consulting Arborist #859
ASCA Tree & Plant Appraisal Qualified
713.385.7040 | www.arboristondemand.com
📚 Sources Cited:
- Shigo, A.L., & Marx, H.G. (1977). Compartmentalization of Decay in Trees. USDA Forest Service.
- International Society of Arboriculture. (Best Management Practices: Tree Pruning).
- Appel, D.N. (2001). The Role of Wound Dressings in Oak Wilt Management.
