Michael L. Agnew, PhD, is Senior Field Technical Manager for Syngenta Professional Products, Greensboro, North Carolina. He is coauthor of Mathematics of Turfgrass Maintenance, Fourth Edition (Wiley). Nancy H. Agnew, PhD, is Student Programs Instructor at Longwood Gardens, Inc., Kennett Square, Pennsylvania. She teaches a course in horticulture mathematics. NICK E. CHRISTIANS, PhD, is University Professor of Horticulture at Iowa State University, Ames, Iowa. His previous books include Mathematics of Turf-grass Maintenance, Fourth Edition, and Fundamentals of Turfgrass Management, Third Edition (Wiley). Ann Marie Vanderzanden, PhD, is Associate Professor of Horticulture at Iowa State University, Ames, Iowa. She is coauthor of Landscape Design: Theory and Application.