Bark usually splits from winter temperature swings, from injuries such as mower or trimmer strikes, from insects working under the bark, or from disease and internal decay. Where the crack sits and whether it oozes, sinks, or shows holes points to which cause is behind it.

Why does bark crack in the first place?

Because something stretches, strikes, or attacks it. Sharp temperature swings, wounds from lawn equipment or construction, insect tunneling, and internal decay or disease are the causes TreeHelp's stress checklist links to cracked or splitting bark.

How can a frost crack be recognized?

By a split on the side of the trunk that faces the most winter sun. Known as frost cracking or southwest injury, it follows winter temperature swings, is hard to prevent, and leaves the area open to cracking again. Young and thin barked trees are worth protecting from winter sunscald.

What does injury or insect damage look like?

Wounds low on the trunk often trace to mowers, trimmers, or construction equipment. Small holes or tunnels in the bark, sap oozing from the trunk, or sawdust at the base point instead to boring insects.

When is a crack a sign of disease?

When the bark around it turns dark and sunken, dies and flakes off, or weeps sticky sap. That is a canker, an infection that enters through injured bark from sunscald, cold damage, insects, or poor pruning cuts. Where a canker sits on the trunk, Garden Phos with Pentra Bark is mixed as a trunk spray, saturating the bark from about 6 to 9 feet up down to the ground, and only while the tree is actively growing.

Frequently Asked Questions

Will a frost crack heal?

Partly. The tree can grow new wood around the split, but the cracked area stays vulnerable and repeat cracking in the same spot can cause major damage.

When is a cracked trunk dangerous?

When the damage is severe or deep. A certified arborist should judge a trunk with major structural cracks, a lean, or large dead limbs.

How are branches with cankers pruned?

In dry weather, cutting 6 to 10 inches beyond the canker. Tools are sterilized in a bleach and water mix between cuts.

What helps once boring insects are found?

A systemic soil treatment, which the roots take up. For 12 months after a single pour at the base, Once A Year Insecticidal Drench with Merit protects against borers and other listed pests.

Can mulch lead to bark damage?

Yes, indirectly. Mulch piled against the trunk can shelter mice that chew bark, so a gap is left between the mulch and the trunk.