IDENTIFICATION – Frost cracks occur in trees during winter when the sun heats the sap enough to cause it to flow through the trunk. But when nighttime temperatures drop quickly, the sap freezes in the trunk. Like water freezing, the sap expands and cracks the bark, which can provide an entry point for pathogens.
FAVORITE CONDITIONS – Frost cracks are more likely to occur on the sunniest side of the tree. Typically only young trees or those with thin bark, such as young maples and crabapples, are affected. Older trees have thicker bark that insulates the sap from the solar heating.
CONTROL – The best way to prevent frost cracking is to wrap the trunks of susceptible trees. In late fall or early winter, wrap the trunk with a light-colored paper or fabric wrap. These wraps are available at garden centers and nurseries. You want the wrap to be light colored to reflect the sunlight, not absorb it. In the spring when temperatures have warmed again, remove the wrap to prevent insects from making their home under it.
Trees can live normal lives with frost crack damage. In the spring following the damage, the tree will begin to grow callus wood over the edge of the crack. If the bark around the crack is jagged and rough, you can smooth the area to help the tree recover. Take a sharp knife or razor blade and cut away the jagged or loose bark. Be careful not to cut into the wood underneath the bark. It’s not necessary to tape or paint over the wound — these won’t help the tree recover from the damage. The callus wood will guard the rest of the tree from possible infection. The crack will likely never close up again, but the tree will be protected.