This article is Bermuda turf specific (the most common turf in Atlanta):
A lot of people, especially lawn enthusiasts and new home owners, are eager to start mowing their lawns in the spring. Maybe they are all rested up after all the down time over the winter. Many, however, end up waiting too long to begin mowing, believing that they must wait until the lawn greens back up before mowing. This seems logical, a perfectly understandable assumption, but a mistaken one, nonetheless.
In the fall as the soil temperature drops the turf goes into dormancy. All of the plants resources are drawn back away from the top growth, and is instead pulled back into the root system. Kind of like a bear in hibernation. This causes the turf to turn from green to a dull tan color. This top growth is basically dead and is in the way. It is blocking the sunlight from reaching the new growth below and is crowding out the fresh growths ability to expand upwards and outwards to blanket the soil again in green.
You might think to cut the grass extra low at the end of the year to prevent this. Well, many do, but that is not advisable. Many weeds thrive in the cooler months, and would like nothing better than to over run your lawn like a plague. A robust layer of dormant turf will help to prevent invasive weeds from getting established in your yard. A thick winter coat of dormant grass will also help to keep the soil a bit warmer, which can be beneficial for the root system. A thick lawn, even while dormant, also helps to slow the process of soil erosion. You probably noticed this year that Atlanta does tend to get a lot of rain in the winter.
So, when to start mowing? Your best bet is mid to late March, but every year is a bit different. For best results, bag up the dormant grass clippings and dispose of them. Clippings from dormant grass are hard on your mower’s engine, hard on your mowers blades, and hard on your lawn. (Pro Tip: Try mowing the lawn in waves. Mow a little off the top. Then mow a second and even a third time if needed. Trying to do it all at once is generally frustrating and as I said before, very hard on your mower. A second pass will help to vacuum up stray clipping that initially evaded your mower’s bag.) Once you have gotten this old dead turf out of the way it will open up the new growth to the air and sunlight, and give it room to grow tall and thick. This will provide you with a greener and healthier lawn.