Bark splitting

Many trees have noticeable splits in the bark of their trunks or limbs. There are a number of potential causes.

The outer layer of bark is a dead protective layer. As the trunk grows outward adding a new bark layer the old layer may split or slough off. This is especially noticeable in some trees, like river birches, white oaks and shagbark hickories.

The trunk of a shagbark hickory, Carya ovata.

Tree species with thin bark, including, ornamental cherries, maples, and fruit trees, can be damaged by sunscald or frost cracks. Damage by both sunscald and frost cracks will always be on the side of the tree receiving the most sun… the south or southwest. The temperature of bark receiving sun can change drastically in a short period of time. This causes tissue to shrink and expand and could rupture the bark. Frost cracks are likely to form in previous injuries.

Normal bark splits in a red maple, Acer rubrum.

Usually these splits are harmless and the tree heals itself. However, it can allow decaying fungi or wood-boring insects to enter, especially if it hasn’t healed in the spring and summer when these organisms are active.

Sunscald on the trunk of a peach tree, Prunus persica.

Some activities make trees more prone to bark splitting. Over-pruning limbs can suddenly expose more bark to the sun without giving the tree time to adapt. It is better to gradually prune any unwanted limbs, if you have to prune at all. Fertilizing, particularly with nitrogen, at the end of the growing season (late summer, early fall) can induce growth, making the tree more susceptible to bark splitting and frost damage. Trees that do not get adequate water during the growing season may be more prone to bark splitting damage.

Frost crack in the trunk of a black cherry, Prunus serotina.

A frost crack that has developed in a red maple, Acer rubrum. Although ugly, the tree is still able to efficiently translocate sugars and nutrients. However, this opening has allowed fungal rots to decay the heartwood and carpenter ants are nesting in the rotting wood.

Fruit growers prevent bark splitting by painting the trunks of their fruit trees with a white reflective paint. This will buffer the trunk bark from excessive temperatures during the day.