The best time to trim a tree is in late winter or early spring. Tree sap rises in the spring and it is okay to prune a tree during this time unless you see the sap "bleeding" from the bark. If the sap is visible, wait until it dries to prune.
About this Author
Bobbie Brewer has been writing since 1990. Her work has appeared in publications and on Web sites including Garden Guides and Trails. Brewer is an international traveler, outdoors enthusiast and has been gardening since 1991. She has a Bachelor of Arts in English from California State University, Sacramento.