Fall fertilization and cold hardiness in landscape trees

Abstract

Fall fertilization is sometimes considered a predisposing factor for winter injury in urban landscape plants. This study was developed to determine if fall fertilization of selected landscape trees would affect winter hardiness. Over a 3-year period, 200 trees in Charlotte, North Carolina, U.S., were fertilized with 1.3 kg N/100 m2 or 2.7 kg N/100 m2 (3 or 6 lb N/1,000 ft2) from Bartlett Boost™ (28-9-9), 1.3 kg N/100 m2 (3 lb N/1,000 ft2) from urea (46-0-0), or left untreated as controls. Fertilizer was soil injected in September or October, and samples were collected at three times during the winter to determine cold hardiness. There were no reductions in hardiness for sawtooth oak (Quercus acutissima), trident maple (Acer buergeranum), or leyland cypress (X Cupressocyparis leylandii). Crapemyrtle (Lagerstroemia indica), which is marginally hardy at the test location, and red maple (Acer rubrum) experienced statistically significant, but not biologically significant, loss of hardiness in January and February due to some fertilizer treatments.