Winter survival of St. Augustinegrass cultivars

St. Augustinegrass [Stenotaphrum secundatum (Wait.) Kuntze] has low freezing tolerance and suffers winter injury in the southeastern United States. Laboratory methods have determined that the lethal cold temperature of St. Augustinegrass stolons and buds is between -4.5 degreesC and -7.7 degreesC. The field survival of St. Augustinegrass to winter freezing is poorly known because most field reports have been based on a single location experiencing a single winter minimum air temperature. The objective of the study was to assess the winter survival of St. Augustinegrass cultivars across a range of winter minimum air temperatures occurring in experimental plantings at 24 Florida counties, following a severe Arctic cold front that moved through Florida beginning 21 Dec. 1989. Except for two counties, the limit for St. Augustinegrass winter survival was a minimum air temperature between -6 degreesC and -9 degreesC. Based on a nonlinear estimate using a 3-parameter sigmoidal model (r(2) = 0.70, P < 0.0001), 50% survival of St. Augustinegrass would be predicted at -7.9 degreesC. Time since planting had no relationship with survival. Differences among St. Augustinegrass cultivars were observed at only two counties.