ASK THE HORT AGENT
Question Should I use wound paint after pruning trees and shrubs?
Answer It depends on who is wounded. Iíve seen pruning wounds that required stitches as well as wound paint.
Gardeners have a tendency to personify plants. While I donít know if a tree has a soul, Iím certain it responds to wounds differently than animals. Trees donít ďheal;Ē they compartmentalize. In other words, they seal up or block off problem areas. Therefore, damaged areas remain encased within trees for the remainder of their lives. Similar to the way a personís lungs handle tuberculosis. While true, it is this type of comparison that blurs the line between animals and plants.
In the past, it was thought that pruning paint (aka wound paint) minimized sap loss, encouraged healing and kept out diseases and insects. These were the ďbenefitsĒ of doctoring your plantís wounds.
Now we know leaking sap actually prevents decaying organisms from entering a wound. We also know that animals die from excessive bleeding because they are losing blood which supplies oxygen to cells throughout the body. Plants are not losing blood or oxygen when they leak sap (aka bleeding). In other words, they arenít really ďbleeding.Ē
Band aids do encourage the healing of a scratched finger, but wound paint may actually slow a plantís natural process to heal itself. Trees use callous tissue to block off wounded areas. Some wound paint actually slows the development of callous tissue. When it comes to pruning, placement of the cuts influences callous material far more than anything else.
It is logical that pruning paint keeps out diseases and insects. After all, it is a barrier. Well, research shows that some diseases are actually trapped between the paint and the plant. The paint prevents the tree from expelling the diseases naturally. As far as insects, most trees should be pruned during the winter or very early spring. At these times, insect pressure is very low.
Luckily, most trees and shrubs do not need extensive pruning. It is best to reduce the need for pruning by proper plant selection and training trees when they are young. Shaping small branches when they are young is better than whacking large branches when they are mature. Hmm. Here is another case where trees are similar to humans. It is easy to see how people humanize trees.
Tree pruning is both an art and a science. The ďartĒ part is not referring to the wound paint, because the ďscienceĒ part says itís not necessary. For more pruning info, visit http://aggie-horticulture.tamu.edu/extension/pruning/pruning.html If you donít have internet access then call me at 910-893-7533 or email me at firstname.lastname@example.org
I donít think leeches were ever used on trees, but Iím sure their use would have extracted the same amount of ďpoisonĒ from the trees as they did from people.
Gary L. Pierce
Horticulture Extension Agent