Richard Tsong-Taatarii, Star Tribune

Why do trees fall? Check water, roots

  • Article by: MARTIN HELLER
  • July 28, 2013 - 6:33 PM

I have been studying why large trees are falling after severe storms for years — not only here in Minnesota, but in other similar areas across the country (“Storm helps turn city into a lab for why trees fall,” July 26).

In the majority of cases, trees have fallen due to insufficient water to the lower root system. If the trees do not get deep enough watering to establish a strong hold deep into the soil, they will get top-heavy and will fall over with the combination of shallow roots and rain loosening the topsoil.

Those large trees that topple should have a root structure that is at least 10 feet or more below the surface to hold them erect. Large trees need supplementary watering in their growing period every two weeks. Local rains do not penetrate deep enough for the older trees.

If you see trees with roots showing above ground, you can bet that they are not getting their proper watering. Those surface roots are not the feeder roots that help the tree grow and establish itself.

Tree roots that get insufficient watering, instead of traveling down deeply for strength, will curve up toward the surface looking for moisture. Notice how many fallen trees have a curved root ball showing. In most cases, there was not enough rainwater to penetrate to the lower roots deep enough to hold the tree in place.

Trees near roadways and sidewalks and other similar root- and water-inhibiting barriers are the ones that suffer the most. Those in private yards planted on higher grade, where water runs off instead of into the ground, are also subject to toppling. The simple answer is to determine the watering needs of your trees and water them deeply during the summer months.


Martin Heller is a retired horticulturist, lives in Plymouth.

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