Tree owners who have broken limbs in their trees or just taking advantage of early pruning opportunities may notice that large amounts of “water” which seem to be pouring out of the branch. This is actually “sap” seeping out of the damaged area. This is sap that would have been going into the limb or branch that was removed. However, since the limb is no longer there, the sap has nowhere to go but out of the freshly cut limb or wound.
Spring weather signals trees to come out of dormancy and all trees start pumping water, minerals, and carbohydrates upwards into the tree, to allow growth of buds, leaves and shoots and will continue throughout the growing season. Certain tree species, such as maple, birch, dogwood, and elms, have an exceptionally heavy sap flow in the early spring. When pruned or wounded, these trees will "bleed" and is quite noticeable. Under normal circumstances, it is best to delay pruning these trees until later in the growing season, when the flow of sap is slower.
There is no need for alarm if this sap flow occurs and the overall health of the tree is not going to be affected. The "bleeding" may be objectionable from a cosmetic standpoint, especially if the sap is dripping directly onto people, cars, or other targets beneath the wounded area. As the affected area on the tree develops callus material and naturally seals off the wound, it will slow the flow to a stop.
It is not recommended to use any type of wound dressing or covering as this will impede the ability of the tree to seal off the damaged area. Be patient and allow natural healing of the wound to occur. Always use good pruning practices and minimize the size of cut branches to reduce wound size on the tree.
Refer to the following Purdue Extension publication Trees Need a Proper Start: Prune Them Right for more information.
Other resources can be found at the Purdue Extension, The Education Store:
Pruning Ornamental Trees and Shrubs
Lindsey Purcell, Urban Forestry Specialist
Department of Forestry and Natural Resources, Purdue University