Girdling Roots

Someone emailed me asking for my opinion on some nasty looking roots in their landscape. Girdling roots may sound like a personal hairstyle problem, but it actually references a common problem in the human landscape not seen much in nature.

Girdling roots are roots that grow in a circular pattern around the main stem of a woody species at or just below soil surface. As the encircling root and trunk flare grow and expand outward, thickening up, they eventually collide into one another, with each placing increasing pressure on the other’s cambium tissue, restricting and ultimately crushing to death the crucial growing tissues. This prevents resources from flowing up and down the trunk: water and nutrients up to the crown and sugary goodness down to the starving root mass. What can result? Smaller leaves, thin canopies, bark splits, stressed plants susceptible to pathogens/pests, and rot leading to the stem snapping at the base are all possible outcomes. Trees with well developed girdles can go on to decline slowly over several years, leading to death of the tree!

How does this happen, you ask? The problems usually start in the nursery, continue on when poorly planted, and ultimately end in death (did I mention that already?) unless there is remediation in the “maintenance” phase of the growing process. Plants grown in standard nursery pots are especially prone to circling roots. Balled and burlap, B&B for those in the know, grown in the field are not necessarily better, for different reasons. Sometimes during field production, but especially while the plant is being dug up and the root ball wrapped, machinery ends up piling soil around the trunk with a resultant buried stem. Classically, the average landscaper or homeowner purchases the plant and installs it just as it is, wrappings intact. What happens? Well, for one, new roots begin to grow directly from the newly darkened trunk where none were before. These new roots become the girdling roots of tomorrow. For two, the buried trunk is usually planted too low, stressing the plant if not sending it into a slow decline. It is critical to remove the top portion of burlap from the ball, scrape back the added soil until the root flare is discovered. This will tell you how deep to actually dig your hole (only as deep as the ball and 2-3 times wider). While exploring for flares and such, examine the root structure for any established or potential girdling roots and remove them prior to inserting the new love of your life in delicious loam. This is, of course, not the only cause of root encirclement, but is one of the most common.

What if your tree is already in the ground and it is showing signs of girdling? First, it is important to relieve the pressure the offending root is placing upon the trunk flare. Second, try to ascertain and ameliorate the original cause of the girdling. To release pressure on the root flare, one needs to cut the root ideally completely out to the width of the trunk at least.

There are several ways/methods/tools one can utilize to deliver trunk relief. A mini sledge hammer and wood chisel method may be the simplest and most effective methods. I have used loppers and saws (powered and hand), however, sawing into the ground quickly dulls a blade, and overly long blades can damage desirable portions of the tree. See the embedded links in this article for upper root/shoot diameter guidelines and conditions upon which one can remove a root(s) without causing more harm than good. 

Once the nasty roots are removed, attempt to diagnose why this happened in the first place. Was it planted too deeply? Is the soil compacted or are there other hard surfaces preventing roots from reaching outward? Is there too much mulch or plant material up against the trunk? If the mulch was piled too high or deep, simply pull back the mulch to find and expose the flare. If the situation is dire, you may have to call a professional arborist to employ an air knife to remove enough soil or break it up. We have several mature trees on the property with trunks going straight into the ground, no flare. Years of soil grade changes have buried the tree, sending it into slow decline. 

Girdles went out of fashion years ago; so should your root restrictions. Cut loose those trunks before problems really flare up in your landscape.

Josh Steffen, Horticulture and Facilities Manager

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  1. Palms do not get girdling roots. Well, the roots can circle inside their can, but then get replaced by new roots after planting into the ground. It seems weird, but they do not even need their circling roots to be severed. Some of the Ficus do not care of their roots are circling either. New roots simply absorb the circling roots. Some trees are just more tolerant of girdling roots. Oaks, pines and eucalyptus are all very susceptible to girdling roots.

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