Regional Gardening Reports :: National Gardening Association

In the Garden:
Northern & Central Midwest
July, 2011
Regional Report

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This tree split because of a poor branch angle.

Storm Damage

So many areas of the country have seen severe storm damage this season, including my town. As I drove around after our last wind storm, I looked more closely at trees that were damaged. A few interesting characteristics emerged.

"Trash Trees"
First of all, trees that lost major limbs were mostly what arborists commonly call "trash trees". I dislike that term since I feel that there is worth and dignity in all trees, but there are a few species that are more prone to problems than others.

Slow-Growing is Best
Generally, trees that grow quickly tend to have weaker stems and branches than slower-growing trees. Lignin is the material that gives woody plants their structure, and the more lignin laid down in the cell walls means a sturdier plant. Growing slowly means plenty of time for lignin to be acquired.

Fence Row Trees Not the Best
We all know how often silver maples, Siberian elms, willows, and green ash trees pop up in fence rows and shrub borders, starting out as saplings and very quickly turning into large trees. Their fast growth should indicate that they are not prime trees to have in our landscapes. Good things are worth waiting for, and this applies to tree choices as well as other things in life.

Insects and Disease
Other damaged plants had disease or insect problems. I found this in my own damaged trees. Two oaks lost fairly large branches, and since oaks are slow-growing and strong, I looked more closely. Both branches were hollow, having become this way because of insect damage early in their formation. It was only natural that strong, twisting winds would snap them off.

Norway Maples
Norway maples in town had a lot of damage, and these trees are prone to a disease called verticillium wilt. This is a fungal disease that eventually chokes off and kills branches. However, before the branch actually dies, it becomes quite weak. Again, strong winds naturally snapped these branches off. If you lost a branch from your Norway or Schwedler maple, take a look at the interior of the branch. Verticillium is indicated by dark staining in the layer just between the bark and inner wood.

Structural Flaws
Some trees that came down or had major damage had obvious problems with structural integrity. Branch angles in a deep V shape are quite weak. Strong angles are those closer to ninety degrees. Some plants such as ornamental pears naturally have poor branch angles, but when planting a young tree, you can have some effect on the integrity by pruning selectively for wider branch angles.

Shallow Roots
Some trees are naturally shallow-rooted, making them candidates to tip over. Douglas fir and Colorado spruce fall into this category.

We can't do anything about the storms that come through, but we can select our landscape trees carefully and get to know the ones we already have. Then it's simply a matter of learning to tolerate "nature's pruning" and cleaning up the mess.

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