Rules For Cutting Big Roots

I’ve been getting a lot of questions lately about cutting roots away from mature trees. So, it’s time to reissue the rules I live by and that most tree experts I know have recommended. These are not the only guidelines that exist, just the ones I’m familiar with.

These suggestions are not going to answer every question about root cutting. But they have served GardenLine listeners and my online followers well for years. There are no one-size-fits-all answers, but start with this: Do not take out more than one big root per year on a mature tree.

And before you jump out there with an axe or machete to whack out that one big root, know that it will be an effort in futility if you don’t get that tree on a deep-root watering and feeding program. If you’re unfamiliar with that concept, and you have an unquenchable desire to start severing roots, read this tip sheet first.

Big roots above ground, other than the tree flare at the trunk’s base, are anchor roots. If they are pushing themselves up to the soil surface in search of moisture, that’s proof of the need for deep-root watering. And since they are “anchoring” the tree, that’s why you can only prune out one big one a year!

And you really shouldn’t do this kind of work yourself, unless you have direct experience as an actual tree expert. Why? Because it’s really much harder than it looks. And if you get overzealous, you could do more harm than good and destabilize the tree.

Some folks think they have to “root prune” because they fear roots are headed toward a sidewalk, a driveway or the house foundation. If that’s your worry, you actually need a root barricade. To successfully stop concrete movement in sidewalks and driveways or to prevent roots from sucking moisture from under a foundation, call a professional.I don’t normally recommend root barricading to protect sidewalks, but it’s another matter for driveways and foundations. Call the radio show, and I can hone in on who might be best in your area to install a root barricade.

And you may be wondering why you can’t just cover all those near-surface roots with dirt, compost or mulch. Again, an effort in futility if you don’t start a deep root feeding and watering regimen. Aside from soil erosion, the number one reason roots are at the surface is because the tree is in dire need of moisture down in the 6- to 18-inch zone, where the root system does its best work. Plus, even if the tree is generally healthy, you should never add more than about an inch of soil or compost to cover roots. If you add more, you run the risk of suffocating the feeder root zone and killing the tree.

By the way, in my world, I find a lot of people hear only what they want to hear. The last time I discussed this topic, someone called the the radio show to take issue with me recommending “only taking out one mature tree per year.” I don’t. It’s one big root per year.