The Rockdale Gardener

Gardening Posts From Rockdale Cooperative Extension

What is causing this circle around my tree?

There are several reasons why a circle might appear in the turf surrounding a tree.

No, not aliens or crop circles.

Sometimes there are many possible scenarios for a landscape phenomena. For instance, here four differing suggestions as to what could be causing the grass turn brown in a circle around this tree.

brown turf encircling tree

Alien caused crop circles or something more mundane?

First reason: Trees can poison plants nearby. Allelopathy is the mechanism whereby one plant poisons another. According to one UGA Agent, “Very early in my career…and in the days before the internet I had a similar situation at a homeowner’s. He had planted two…Chesnut oaks in his front yard and when I went to his house, there were 2 very prominent circles around each tree. You would have sworn that a dog had been tied to each tree and he had constantly run around in a circle and worn down the grass. At the time…our Turf Disease Specialist…told me it was allelopathy, with certain oaks begin worse than others.”

Second reason: riding mowers can damage the grass and create soil compaction where the outside wheel turns when going around the tree. Zero-turn mowers wheigh as much as 1200 lbs. According to another agent friend of mine, “Using a zero turn mower, running too fast or cutting when it is wet could make wheel tracks around the tree.”

Third reason: Another cause could be fairy ring fungus. These fungi grow in a circle preventing water from penetrating into the soil. Grass suffers and turns brown.

Fourth reason: My personal opinion? Trees can out-compete grasses for nutrients and water. The circle in the picture above represents the area where the tree roots are competing with the grass for water and nutrients. I have seen this many times in poorly maintained turf.

In any case, aerating the turf, fertilizing, mulching to the drip-line of the tree and irrigating the turf will likely alleviate the problem.