Spacing should be a tight minimum 3 foot, if you want arching blades gracing the walkway. If the desire is to have no plant material in the walkway, then plant at least 4.5 to 5 feet away. My mature Dallas Blues is 5 feet in diameter, with a height of 5 feet, especially with the morning dew. One of my favorite grasses, and most favorite of Panicum varieties....

Thanks! I will be planting in somewhat compacted soil and nothing much grows to it's normal size in this location, but it would not suprise me if this panicum might. I will take your advice & stay 4.5 feet away from the sidewalk. Thanks again.