Beautiful gardens by William Johnson
A READER recently told one of the county’s master gardeners that one of her pine trees had been struck by lightning during a severe thunderstorm a few weeks ago. She asked if there was anything she could do to save the tree or whether it was likely to die.
Lightning striking a tree in one’s landscape is a traumatic experience for both the tree and its caretaker. After checking to see if one’s own limbs are intact, attention quickly shifts to the tree’s welfare.
In the week after an electrical storm, AgriLife Extension Service offices often field questions from concerned homeowners regarding the prognosis for beloved trees and what care might be given to help them survive or recover.
The question was asked by a neighbor of master gardener Joanne Hardgrove, who was asked about the prognosis for a pine tree that had been struck by lightning in the lady’s home landscape.
Unfortunately, and quite accurately for the concerned tree steward, the best answer to these urgent questions is often that only time will tell but the owner should not give up on the tree just yet.
A lightning strike can affect a tree in many ways. Some are immediately obvious and some are not. Sometimes, the trunk or large branches are splintered. A strike might make continuous grooves in the trunk or main branches.
In many cases, the apparent damage might appear minimal while internal injury to the vascular tissues of the trunk and roots is extensive and gradually manifests itself over a period of months or even years.
In some cases, the majority of the damage occurs to a tree’s main roots as the electrical discharge – up to 100 million volts at thousands of amperes – vaporizes the water inside the roots, creating superheated steam. People standing above such roots during a storm could be electrocuted even though they are standing a good distance from the tree’s trunk.
It is difficult to predict which trees will be struck by lightning and which are most likely to be seriously injured. In general, though, lone trees, those tallest in a group or those growing in moist soil have the highest probability of being struck.
In the considerable body of lightning lore, certain tree species are commonly listed as more lightning-attractive than others. They include maple, ash, tulip tree, sycamore, poplar, oak, elm, pine, spruce and hemlock. Some of these, like sycamores, are likely targets because they tend to tower over other species, while pines and hemlocks can be lightning-prone because of the water that collects on their needles during thunderstorms.
Homeowners typically want to take immediate action to help a damaged tree survive the aftermath of a lightning strike. In most cases, however, there is little that can be done to help a tree recover.
Should one apply any of the various wound-dressing concoctions commonly used? While most do no harm to the tree, over time many dressings develop cracks that can harbor insects or hold water, leading to decay. Applying a wound dressing may make the caretaker performing the operation feel better but it is not recommended.
If the lightning damage creates hazardous broken branches, they should be taken care of quickly. However, in most cases, it is best to wait six months before doing major – expensive – corrective work.
If, during this waiting period, the tree shows no obvious signs of decline, then it might be worth the expense of major corrective pruning. In many cases, it will become obvious at some point during the waiting period that the tree will not recover and that its removal is the best option.
My experience has been that a lightning strike does not automatically spell doom to a tree as many struck trees are able to make a remarkable recovery given adequate care and time.
Another question received recently was from a reader whose back yard has three peach trees of different varieties. All three trees have produced a good crop of leaves this spring but a sparse number of flowers and an even sparser number of fruit. What would cause this to happen?
Despite the cold front that occurred in early January, this past winter was relatively mild. Along with other non-citrus fruit and nut trees, peach trees need a specific number of chill hours each winter to regulate their growth and flowering in order to set their flowers and fruit in the spring.
If a tree doesn’t experience enough chill hours in the winter, the flower buds might open unevenly or not at all in spring.
Chill hours are usually defined as those in a range of temperatures below 45°F and above 32°F; however, some models for calculating chill hours rely on slightly different ranges. Nearly all models take into account temperatures above 60°F during the winter as they will reduce the chill-hour total.
This past winter, we exceeded the 60°F temperature mark on many, many days so air conditioners were running a lot over the season. So it’s really not surprising that peach flowering has been so sparse this year.
William Johnson is a horticulturist with the Galveston County office of Texas A&M AgriLife Extension Service. Visit his website at aggie-horticulture.tamu.edu/galveston/index.htm.
Lightning can inflict significant damage to a tree as it did in March to the pine tree pictured above growing in a home landscape in Clear Lake. Being struck by lightning does not automatically spell doom to a tree as many such trees are able to make a remarkable recovery over time if provided good care. – Joanne Hardgrove