August 26, 2017

1 - Lightning damage to trees may be obvious or subtle, fatal or non-fatal.

Yard and Garden August 26, 2017


I was away from home for a week recently. When I returned home I noticed that many leaves had fallen from my cottonwood tree and those left in the tree were mostly black. I understand we received considerable rain during the time I was gone. Is it possible that the rain has killed my tree?


I received a similar description under similar circumstances several years ago. A friend was away from home and returned to find the leaves of his cottonwood tree either black or on the ground. I suggested that he ask his neighbors if there was a very loud clap of thunder during one of the rain storms while he was gone. The answer was “yes, there was a bright flash of lightning and an immediate, extremely loud, clap of thunder.” This suggested that his tree was hit by lightning, or the lightning hit very near his tree.

Branches may be splintered, burned, or bark may explode off the tree when it is hit by lightning. These symptoms are not always present. In some cases the lightning strikes near the tree and travels through the ground to the tree, damaging roots. In other cases the strike may take a path over the wet bark and not through the sap of the tree. In these cases the bark may not be damaged and the branches may show no sign of the lightning strike. However, the leaves may be damaged.

If the effect of the lightning is not fatal, there is a good chance that the tree will survive and produce new leaves. In the situation described about my friend’s tree, the tree refoliated in August, dropped those leaves in the autumn, and resumed growth in the spring. There were a few branches that died, but in the case of an old cottonwood that may have happened without a lightning strike.

Green wood is a good conductor of electricity. Water on the surface of the branches may be a good electrical conductor. These factors play a role in the damage done by lightning. It also provides a warning to people that branches touching or near a structure may conduct lightning to the structure perhaps causing a fire. Any branches that may conduct lightning to a structure should be pruned to reduce the potential problems. The conductivity of green and wet wood is a factor to consider when pruning trees touching or near high voltage powerlines.

Farewell dear readers - For over 22 years I have had the honor of writing the Yard and Garden column as NMSU Extension Horticulture Specialist and in retirement, but that time is drawing to a close. Dr. Marisa Thompson has assumed the duties of NMSU Extension Horticulture Specialist and will soon be answering your questions in the Yard and Garden column. I will continue writing for a brief period as Dr. Thompson gets settled into her office and the many aspects of her job, but you will notice that it is her contact information provided at the end of this column. I will soon begin writing a garden blog, so I hope I will be able to see my friends online as I do that. I hope to see you at SouthwestGardenSmith, but please also use the resources of NMSU’s County Extension offices and rely on the great expertise of Dr. Thompson. I remain your garden friend, Curtis Smith (SouthwestGardenSmith).

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email:, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.

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