Deciduous trees in winter
In early winter, deciduous trees enter a dormant phase. They drop their leaves, move sugar to their roots, and wait for warmer temperatures to return. During this time, as long as temperatures are above freezing (water is still liquid), water will continue to flow into the roots. Trees will absorb water until water pressure in the tree is equal to the surrounding soils.
Spring – a flurry of activity
When air temperatures rise, the tree is primed and ready to go. It’s flush with water and starts moving sugar from its roots to the twigs, supplying the energy needed to grow new shoots and leaves.
At this point, pruning or damaging a tree will likely result in ‘bleeding’ – sap will ooze from the wound. This may continue for weeks as the tree has a lot of water stored and a potentially limitless supply of water from the neighbouring soil. The sap will eventually stop flowing from the wound, as transpiration rates increase and the water pressure in the tree returns to normal summer levels.
Should I try to seal a wound?
We do not recommend that you seal a bleeding wound on a tree. The products on the market do little more than prevent the sap from oozing, and if the sap flow is quite strong they may not even do this. Sealing the wound does not help the tree, and is likely to trap pathogens in the bark, preventing it from healing naturally. The tree will seal the wound itself in time.
If the wound is caused by natural damage (not human activity) this is especially important – unless you have identified what caused the original wound you risk trapping the pathogen in the tree and causing more harm.
The best advice is that prevention is better than cure. Prune trees at the right time of year where you can, and if your work is unavoidable, leave the tree to heal naturally. Like a human, the tree will seal the cut itself with time.