Trimming Guide For Bleeding Trees
When a tree produces heavy sap after pruning, it's often called bleeding. Bleeding trees can be a concern and a nuisance.
Reasons for Tree Bleeding
"Bleeding" sap is a completely natural response by a tree to wood cuts. Most trees produce some sap, but certain varieties and certain seasons are more likely to cause the heavy sap bleeds that can be so messy and concerning. Maple, willow, poplar, and some conifer varieties are especially known for their prolific sap production at the smallest trimming wound.
Sap runs during the non-dormant period of the year, which is late winter through fall for most tree varieties. Some conifers also have running sap in winter. The sap carries water, sugars, and other nutrients between the roots and leaves. For many trees, spring is the time of the heaviest sap run as the tree rushes nutrients and water to the newly unfurling leaves and developing flowers and seeds. When a tree in high sap is cut, the sap seeps out.
Concerns and Problems
Sap loss typically isn't a concern for the tree, particularly during spring when water and nutrient availability is high. The only time it can pose an issue is if the sugars in the sap attract insect pests, who are then vectors that bring fungal, viral, or bacterial disease to the tree. Even then, most healthy trees will be fine and this is only a risk for very young trees or those that are already suffering.
The main concern with tree bleeding is that it can cause a mess. The sticky sap can coat pruning tools and hands, and it is difficult to clean off. Dripping sap can get all over your siding, windows, drip onto your car, or destroy your patio furniture. For most people, the issue with bleeding trees is the effect on things other than the tree.
The most often given advice is to prune trees in late winter. For heavy bleeders, though, this will result in heavy sap production from the wound as soon as the tree breaks dormancy. Instead, wait to prune these trees until late spring or early summer — after flowering and once the leaves have reached their mature size. Less sap is running at this time, but there is still plenty of growing season left for the wounds to heal.
Further, trimming cuts must be clean. Cutting branches back to the collar at the trunk or making pruning cuts in front of a bud encourages quick healing, which in turn reduces sap loss.
Contact a tree trimming service in your area if you need more help with high sap tree pruning.