MENUWinter recently began. What kind of winter can we expect in this unpredictable year? Knowing the answer to that will give us insight into what kind of tree and shrub damage we can expect. It will also help us to plan our winter work.
It has already been reported that this will be a La Nina year. NOAA (National Oceanic & Atmospheric Administration) defines La Nina as a weather pattern that occurs in the Pacific Ocean. It results in strong winds that blow warm water at the ocean's surface from South America to Indonesia. La Nina, which is the opposite of El Nino, is a weather pattern that can occur in the Pacific Ocean every few years.
These patterns, though thousands of miles west of us, influence our weather and our landscape plants especially our trees. Although La Nina generally means that we can expect a cold, wet winter, at least one Rochester meteorologist has been indicating that we’ll have short term cold snaps, frequent spells of mild weather and episodes of snow to rain and back to snow. It’s also predicted to be windy.
For most of us, a partially mild winter is a good thing. For our plants it may not be so good. Plants don’t like weather that oscillates back and forth from cold to mild. Those freeze/thaw cycles that we take in stride may result in trauma for some trees.
Frequent freezing and thawing can cause the fluids inside a tree to contract when they get cold and expand when they get warm. When these cycles become extreme, the expanding fluids can cause the bark to crack vertically. This is especially true for trees with smooth, thin bark. Frost cracks can become entry points for insects, diseases and rot-causing fungi.
There is no treatment for frost cracking. Healthy trees will form a callous around the wound as a defense against insects, diseases and other pathogens entering the wound. A customer owns the pictured ginkgo tree that he rescued from the trash heap. The tree developed the frost crack in the nursery. It has survived for about 25 years, including one move, 20 years ago, from the customer’s former home to his new yard. We deep root fertilize it once a year and prune it periodically and it’s very healthy.
Freeze/thaw cycles may also result in soil heaving as water in the soil contracts and expands. Damage may be mild heaving of the soil around the tree or shrub’s root zone. More often, however, the heaving will be sufficient to break roots, causing the tree or shrub to lean. In the most severe case, the tree will topple, especially if it’s shallow rooted.
We can often repair soil heaving damage if the tree is just leaning. On a warm day, we will examine the roots and then stand the plant upright and stake it. In the spring, we’ll determine whether the plant is able to regenerate enough roots during the growing season to stabilize itself after being staked for a year. We may opt for removing and replanting it or it may have to be removed. Toppled trees almost never can be righted and have to be removed
