Frost Crack
Temperature Abiotic disorder
Last updated
This profile contains basic abiotic disorder data. Regional field notes and expert review are in progress.
What Causes It
Frost cracks form when rapid temperature drops cool the outer wood of a trunk faster than the inner wood, generating differential contraction between the two. Stress accumulates along the grain until the outer wood splits, usually vertically and usually on the south or southwest side of the trunk where daytime solar warming and nighttime radiative cooling produce the steepest temperature gradients. Once a crack has formed, subsequent freeze-thaw cycles tend to reopen it each winter, producing the raised ridges of callus known as frost ribs. Frost cracks are most common on thin-barked species and on trees with wounds, included bark, or previous injuries that concentrate stress at a discrete line. [VERIFY] Mechanism described here is the standard horticultural explanation; HFG library does not document frost cracks quantitatively.
Quick Reference
Symptoms
Vertical splits along the trunk, typically on the south or southwest side, often several inches to several feet long. Split may reach from the bark into the sapwood and sometimes to the heartwood. Raised callus ridges (frost ribs) form along the crack as the tree attempts to heal, and subsequent winter cycles often reopen the same line. Bark along the crack may be loose, discolored, or separated from the wood beneath. Cracks may bleed sap during spring warming. [VERIFY]
Vertical orientation, south or southwest exposure preference, callused ridges from prior cycles, and absence of decay fungi or insect evidence at the initial wound. Mechanical wounds and lightning strikes can produce similar splits but usually show additional evidence (point of impact, staining, specific geometry).
Timeline: Initial cracks form during the first severe cold event after a warm spell. Subsequent winters reopen the same crack and progressively build callus ridges. Damage is visible year-round once present.
Triggers & Conditions
Rapid temperature drops during cold winter weather, especially after a sunny warm afternoon followed by a clear cold night. Most severe on south and southwest trunk exposures, on young thin-barked trees, and where the trunk has pre-existing wounds or included bark. The underlying mechanism is differential thermal contraction: the outer wood cools faster than the inner wood, creating tangential stress. When this stress exceeds the material strength of the wood along the grain, the trunk splits vertically.
Winter cold events, especially rapid transitions from warm afternoon to cold clear night. Young trees in their first decade (bark <1 inch thick) are the most vulnerable. The 1-2 weeks following a warm spell are highest risk.
Frost cracks are relatively uncommon in the Puget Sound lowlands because sustained deep cold is infrequent and the rapid temperature drops that drive crack formation are rare. When they do show up, the typical cases are (1) young maples and fruit trees planted with south-facing trunks exposed to winter sun on cleared sites, (2) thin-barked beech and linden specimens in open parks, and (3) older trees with pre-existing trunk wounds that concentrate stress at a line. The 2022 arctic outflow produced some visible new cracks locally; more common is finding pre-existing frost ribs from older cold events. [VERIFY] No systematic documentation in HFG library.
Management
Prevention
- Retain lower branches on young trees to shade trunks
- Apply white trunk paint or wrap on high-value young trees
- Avoid mechanical injury to trunks
Plant thin-barked species on sites protected from direct winter sun on the trunk. Retain surrounding canopy or hardscape that casts winter shade on trunks of vulnerable specimens.
Plant Tolerance
Thin-barked young trees of many species, particularly maples, beeches, lindens, fruit trees, and other smooth-barked hardwoods.
More Tolerant
- Mature trees with thick corky bark
- Most conifers
More Sensitive
- Acer species (young)
- Fagus sylvatica
- Tilia species
- Prunus species (fruit and ornamental)
Bark thickness, bark reflectivity, trunk orientation, tree age, and presence of lower branches that shade the trunk. Mature thick bark provides significant insulation; young smooth bark does not.
Secondary Effects
Frost cracks can serve as entry points for opportunistic canker pathogens (Nectria, Botryosphaeria, Cytospora) and wood decay fungi (Fomes fomentarius and other heart rot fungi).
Repeated reopening and callusing weakens the local wood structure and can predispose trunks to storm breakage at the site of the old crack.