How to Dig Around and Trench Through Tree Roots

In our landscape, trees remain a constant comfort. After all, they’ve been there for years, decades or even centuries.

That, of course, means trees don’t budge, even when we may need them to. If you’re starting a construction project, like installing a fence or irrigation system, tree roots can be a challenge.

Lacretia, a Davey blog reader, recently asked, “How can I dig a 3-foot deep trench line near my 100-year-old oak without damaging it?” Below, read the best way to go about this and learn when it’s likely not a good idea to trench through tree roots.

The Best Approach for Digging a Ditch around Tree Roots

Digging a trench around a tree or through tree roots takes a lot of planning, a little math and some help from your arborist.

How do I go about protecting tree roots during construction?

Ideally, trees should be healthy and in good shape before you begin a construction project. In other words, the roots should be well-watered, the canopy free of any dead or diseased branches and the soil stocked with nutrients.

You should also prepare the construction site by checking for any underground utility lines. Contact your utility company, and they’ll help point these out.

What are the guidelines for digging a ditch around tree roots?

Tree roots spread much further than what we can see above ground. Whenever possible, it’s best to start digging as far away from your tree as possible.

If you want a more exact distance, try this!

1. Measure the diameter of your tree. Wrap a measuring tape around the tree, four feet from the tree’s base.
2. For young trees, multiply the tree’s diameter by 3. For mature trees, multiply the diameter by 5. That number will help you determine a safe place to start digging.
3. For example, if your mature maple tree has a diameter of 2 feet, start digging at least 10 feet away from the tree in all directions.

Is it safe to dig through tree roots?

Digging through and cutting tree roots isn’t something to take lightly. Cutting critical roots can interrupt the tree’s water and nutrient uptake, leave permanent damage to the tree's structure and stability, or, in the worst case, cause the tree to die.

When beginning or considering a construction project, start by determining what tree roots you shouldn’t cut.

It’s not a good idea to cut the roots of already damaged trees. Also, roots that are more than two inches wide or close to the trunk should not be pruned, cut or dug through because they help anchor the tree.

Tree age and species will also affect how the plant reacts. Before attempting to cut tree roots, talk to your arborist about what may or may not be safe for your tree. Your arborist can prune the roots for you, or you can follow our step-by-step guidelines for DIY root cutting. Remember, proceed with caution!

Click to read more about how Davey arborists handle tree roots during construction.