Maybe you have noticed that the grass is starting to slow down. However, you may have also noticed that some grass is starting to go dormant. The grass starting to go dormant already are the warm season grasses that have established in this area.
We typically have cool season grasses in Michigan. Kentucky Bluegrass, Perennial Ryegrass, and Fine Fescue are all cool season grasses that are perfectly suited for this climate. They typically grow when the temperatures are between 55ºF and 70ºF. Cool season grasses can tolerate the cold winters in the northern parts of the country. Cool season grasses typically go dormant when temperatures become consistent near freezing.
But the grass that you are seeing go dormant and turn brown already in early October are invasive warm season grasses like Bermuda grass and Zoysia grass. They like warmer temperatures. They typically grow between the temperatures of 75ºF and 95ºF. Once the temperatures drop below 50ºF, the warm season grasses will start to go dormant.
There is no need to worry about parts of your lawn turning brown if you have some warm season grasses in it. They will start to grow again this coming spring. They survived last winter, so they will most likely survive this winter that is to come.