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Garden Help Desk: Trimming surface roots without harming the tree

By USU Extension - Special to the Daily Herald | Dec 2, 2023
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Some trees are prone to developing surface roots that can become quite large. These large roots can interfere with mowing, foot traffic or recreational activities.
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As trees mature, surface roots may appear. If the roots are in an area of the landscape where there is very little foot traffic, it may be best to simply ignore the roots.

I have a spruce tree in my yard that is about 60 years old and has several very large surface roots that I keep tripping over. Is it possible to remove these roots without harming the tree?

It’s not unusual to see an occasional surface root with a spruce tree; they’re known for their shallow roots systems, usually concentrated in the upper 18 to 24 inches of the soil profile. The heavier the soil, the closer to the surface the roots will be.

Roots provide several critical “services” for a plant:

  • Roots collect vital resources like moisture and nutrients needed by the plant.
  • In many plants, roots provide storage for the carbohydrates (energy/food) produced through photosynthesis.
  • Roots anchor the plant in the soil. For taller plants like trees and large shrubs that are more exposed to the effects of the wind, the roots provide a stable foundation.

Removing several surface roots can affect the health, vigor and stability of a tree, especially larger, older trees like yours.

Without enough anchoring roots, a tree could become unstable and fail in heavy winds. Trees in clay soils like those common in our county will have fewer deep, anchoring roots and rely more on their upper roots for support.

A tree can become stressed and begin to decline due to moisture and nutrient issues caused by root removal. Loss of stored nutrients could also stress a tree during spring leaf out when that stored energy is needed for new growth.

So, can you remove any of the roots on your tree? That depends on how many roots you need to remove and how close you need to come to the trunk. Think of your tree’s root system like it was a pie with the trunk at the center and the roots extending out toward the edges of the crust. A root begins at a single point on the trunk, but just like taking a slice from a pie, that one root will have spread out over a wide area of resources the farther it is from the trunk — just like your slice of pie is at the crust. The larger and older the root is, and the closer to the trunk you need to make your cut, the more resources the tree will lose if the root is removed. The farther from the trunk you make your cut, the smaller your slice of “pie” will be.

If your tree is healthy, you can safely remove a root or two if you keep a few things in mind:

  • Don’t root prune trees that have been struggling with other issues.
  • Winter through early spring is the best time to do root removal.
  • The farther from the trunk you make your cut, the less stressful it will be for your tree. Stay about 6 inches away from the trunk for every 1 inch of trunk diameter.
  • Don’t remove more than 15% to 20% of the surface roots at a time.
  • Wait two to three years before removing more roots.
  • Limit root removal to roots that are not more than one inch in diameter. Once roots reach the 2-inch or larger range, the risk of serious problems for the tree is high. A bad cut can lead to worse problems than the ones caused by the surface root. Consult a certified arborist instead of attempting to remove a large root on your own.

If you’re going to remove a root on your own, first identify your pruning target (the location where you’ll make your cut). Dig around the target location and the part of the root you plan to remove until you’ve exposed the surface root. Make your cut with a sharp pruning saw and then gently pull away the root. Fill in and level the disturbed soil. In the spring, you can reseed or resod that area.

Maybe removing those surface roots isn’t the right choice for your tree, but what can you do to solve the tripping problem without losing your tree? There are a few options to consider.

You can remove the grass within the problem area and replace it with 3 to 4 inches of bark nuggets to establish a level surface again.

If you don’t really need the area for yard activities and you’ve only been tripping because you need to mow the lawn, you can remove the grass in this area and replace it with a water-wise ground cover.

If you must have lawn in the area, and you’re careful and patient, you can gradually raise the soil level next spring by adding a half-inch layer of soil over the lawn in that area. Repeat the soil addition every month or two as the grass grows up through the soil. Don’t exceed 3 inches of total added soil (the less soil you add, the better for your tree).


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