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magnolia tree root systems and damage potential

Does a magnolia tree root system cause cracking on the house foundation if planted too close, especially on clay soil?

What kind of magnolia are you growing? Is it deciduous or evergreen? Is it large species or one of the smaller varieties?

According to SelecTree, a website of the Urban Forest Ecosystems Institute, most Magnolias have a low root damage potential. A few, such as Magnolia delavayi, are rated as moderate. I am not an arborist, so I cannot conclusively tell you that a Magnolia will not be problematic for the house foundation. However, it is always a good idea to plant trees far enough away from structures so that you do not have to do a lot of pruning to keep them from conflicting with windows, entryways, the roofline, etc. From what I have read, most tree roots that harm foundations are not themselves causing the cracks, but are exploiting preexisting weak points in the foundation. Roots do expand in size as the tree matures, and they do seek out water to some extent, depending on the type of tree.

Below are some links to information that may be useful to you.

North Dakota University Extension (no longer available online)
“How close to the home should trees be planted?

Large trees such as ash, hackberries, maples, lindens and oaks should be kept at least 20′ from the foundation. Medium sized trees such as buckeyes, honeylocust and little leaf linden – 15-20 feet away and small trees such as flowering crabs, mountain ash and Canada red cherry – 10 feet from the foundation.

Do tree roots actually crack the foundation?

No, the wetting and drying of the clay soil causes the initial cracks. After these have developed, tree roots will grow into the cracks for moisture.”

A personal essay on tree roots and foundations, from Renegade Gardener,a garden blogger

International Association of Home Inspectors
“Tree Roots and Foundations

Contrary to popular belief, InterNACHI has found that tree roots cannot normally pierce through a building’s foundation. They can, however, damage a foundation in the following ways:

  • Roots can sometimes penetrate a building’s foundation through pre-existing cracks.
  • Large root systems that extend beneath a house can cause foundation uplift.
  • Roots can leech water from the soil beneath foundations, causing the structures to settle and sink unevenly.”