What length of grass do we have in our swales? August 16, 2017 B What length of grass do we have in our swales? The length of grass in the swales will vary depending on the time of year but will generally be at apron height, between 10mm and 12mm. Share: AGC Greens Section Editor Older Post Do we cut our rough to a standard length over the whole course? Newer Post When will the proposed changes to the course take place?