Shigo taught new ways to look at trees
Dr. Alex Shigo, author of ?A New Tree Biology,? died Oct 6, 2006. I mention his passing for several reasons.
I know that several from around here attended his workshop he offered a few years ago in Nashville. He tried to teach us a new way to look at trees: from branch removal to how wounds heal; so that we may provide trees with better care. Man sure can harm trees while getting paid to care for them through ignorance.
I started thumbing through the pages of his book after recording his death in it. I stopped to read some of his statements that I had highlighted over the years. I will quote and paraphrase a few of them that are pertinent to nursery and landscape. My comments will not be in quotation marks.
?When trees are grown in containers, problems that seldom occur in the natural forest begin to develop. The twisted, girdling roots shown here are from a tree grown in a small container. The figure shows a primary root wrapping around where the trunk flare will be. Once the roots begin to entwine the trunk, the pattern will continue. On young trees, the girdling roots should be removed.?
?Girdling roots are a man-made problem. Growing trees in containers … causes new problems. This is a perfect example of new tree problems brought on by new technology. … When planting into a machine dug hole, it can be like planting into a container, especially when the sides of the hole are slick, smooth and compacted. Clay soils will be worse. Future girdling roots will begin.?
?When planting, the native soil should be loosened much wider than the ball width, grass should be kept away and the soil should receive only small amounts of amendments. Recent research says no amendments unless amending the entire bed. Fertilizers should be applied after the tree is established. No moat for catching water should be made. The tree should be braced, but not so tight that it cannot move. Wire through a rubber hose will still injure bark.?
?Why trees are wrapped with burlap and cloth is a mystery to me. He is not referring to the temporary protection we provide for shipping. Studies show that these materials do little except hide wounds and provide a home for several types of insects.?
?Problems with roots are usually not recognized until it is too late. Yet root problems are some of the most serious problems trees have today. Shigo wrote this in 1986 and it is still true. If we knew all there was to know about the above ground parts of a tree, we would still only know half of the whole story.?
When cutting a branch from a trunk, making the cut flush to the trunk is referred to as a flush cut. I guess many like the appearance and assume it to be a good method. A hawkbill knife was used to make flush cuts on young trees. We now know this is harmful to the tree, though the wound did heal.
Shigo devoted a chapter to branch removal and showed many photos of before, after and of the trunk split open to show how the wood healed properly or improperly because of improper cuts.
?Flush cuts are more injurious on some species than others. … Improper pruning cuts started the problem and the sun or heat or cold did the rest. … The flush cut is a type of predisposition. … It is not the size of the flush cut that makes it so injurious. It is the fact the cut removes the protection zones and also exposes the trunk tissues. …
?The point must be emphasized strongly that stubs, even small ones, should not be left after pruning branches. This is especially true for small trees in nurseries. … be very careful with any type of pruning tool that crushes or tears the bark, …
?Proper pruning does take skill and practice, but like any art form, once learned, the person can operate very quickly. … The longer stubs make perfect home sites for insects and potential pathogens.?
There is a swollen area around where each branch is attached to the trunk. It is referred to as the branch collar and contains the protection zones and the cells that generate the callus tissue that close the wound properly. Making a flush cut removes the collar and requires more effort. Leaving the collar requires less effort because of less wood to cut through.
?When pruning living or dead branches, the collar at the branch base should not be injured or removed. The best time to prune most trees is late in the dormant season. Cuts should not be covered with wound dressing or sealants.?