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Master Gardener: Seeing strange patterns and swirls in your grass?

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Unusual grass pattern

Unusual patterns on bermudagrass are caused by freezing temperatures.

My bermudagrass has some pretty crazy patterns in it currently. I’m not really sure how to even describe it — kind of swirly patterns of green and brown. Is my grass dying? — K.L.

I’ve been seeing these patterns around the neighborhood recently. Some people describe them as a leopard print, Zebra turf, wormy, swirly or even as a psychedelic pattern. It almost looks like something underground might be the culprit. However, these patterns are not caused by anything sinister. Instead, they are caused by freezing temperatures.

If you remember (and who could forget), we had a pretty decent early freeze in mid-October. This freeze shut down many of our vegetable gardens about a month ahead of normal. Freeze damage to our bermudagrass or Zoysia started showing up a week or so later.

When the mid-October freeze happened, our bermudagrass was moving toward dormancy for the winter but was still in an active growing state. Due to that early freeze, the tender green grass blades were vulnerable to damage. The curious thing is that the cold doesn’t affect all bermudagrass in the same way — even grass in the same lawn.

According to Dennis Martin, professor and turf specialist at OSU, these patterns tend to occur in bermudagrass that has been mowed at a taller height, say 1½ inches rather than a shorter half-inch height you might find on golf courses. The taller grass provides more insulation, preventing heat loss from the soil. Conversely, it also decreases the amount the soil warms up during the day. Because of this, the grass blades on the taller grass can remain cooler at night as compared to a more closely mowed turf, which tends to stay a little warmer due to proximity to the soil.

So, when we have a freeze before the bermudagrass has gone dormant for the season, the longer bladed grass can get cooler than the shorter grass, allowing it to freeze. When the temperature drops below 32 degrees, the turf tissue can freeze, bursting the active cells in the turf, causing it to die and turn brown.

The unusual patterns in the grass reveal the areas in which the heat rose and the areas where the cold descended. The greener areas show where the heat was rising from the soil through the grass, and the brown areas show where the cold descended toward the soil. It’s kind of like people walking opposite directions in a hallway moving out of each other’s way.

The bottom line is that there is no cause for concern when you see this in your yard. The only parts of the grass affected are the tops, and those were about to go dormant for the season anyway. In the spring, your grass should green up just like you expect. See you in the garden!

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th St. or by emailing us at mg@tulsamastergardeners.org.


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