Why do we recommend wrapping trees at this time of year? It’s not unusual for winter temperatures to reach 60° Fahrenheit in the daytime and then fall below freezing after the sun goes down. When it gets this warm, the low winter sun heats up the tree bark, especially on the south and southwest sides of the tree. The sun’s warming action breaks the trees dormancy and the cells on that side of the tree wakeup and become active. When the temperatures fall after sunset, the active cells and tissue die.
The damaged area will sometimes shrink and discolor. Later in the season, the bark may fall off, leaving a long scar. You should wrap trees for the first six or seven years after you plant them. After that, the bark should be thick enough to reduce the risk of sunscald damage.