If you mow your lawn regularly, you might be in the habit of going in straight lines up and down, starting and ending at the same spots, all season long, without a second thought. But following the exact same pattern week in and week out may be doing a disservice to your grass.
Grass leans and begins to grow in the direction in which it is cut, meaning it'll grow unevenly rather than upright over time. Mowing in the same pattern over and over can also compact soil and create ruts, none of which is good for the health and longevity of your yard.
The best mowing pattern is one with variety
Your mowing pattern doesn't need to be fancy or perfectly precise, nor do you need to go both horizontally and vertically within a single mowing session. The most important thing is that you change direction each time you mow, so you get variety over the course of the season.
Once you've cut a width or two around the edges of your lawn—including trees, beds, and any tight spots—mow the remainder of your grass in horizontal lines. The next week, angle 45 degrees to cut stripes diagonally. Continue subsequent sessions with vertical lines, then diagonal lines from the opposite corner, then back to horizontal. Even alternating between horizontal and vertical is better than cutting the same path week after week.
If you have a robot mower, you can choose a pattern (depending on the model) that will prompt the machine to vary its direction each time it goes out.
Alternating direction each time "avoids wear patterns, promotes even grass growth, and ensures your lawn remains in optimal condition," according to Scott Porteous, a robotics product manager at Husqvarna.
Finally, keep other basic lawn care in mind in your quest for the healthiest pattern: Don't mow it too often (once a week, maybe twice), and don't cut it too short (less than three inches).