ty, the reason for painting the trunks, is in the spring, as the temps start warming, and the warm sun shines on the trees, the sap starts flowing up the trunks, then it re freezes, and the sap expands and can split the trunk. There is less danger of a branch getting enough sap into it, that it will split, and even if it did, you can trim that branch off. You cant trim the trunk.