2018 ASHS Annual Conference

Mountain laurel (Kalmia latifolia L.) is a valuable ornamental shrub due to its attractive foliage and showy flowers. Breeding efforts have led to improved selections that had been developed, evaluated, and distributed in the northeastern United States, but being ignored by nursery people and consumers in the southeastern US. We conducted a four-year trial to evaluate 21 popular mountain laurel cultivars, primarily developed in the northeastern US, for container and field performance in Georgia. All container grown cultivars yielded considerable growth in the first year, indicating growing mountain laurel as one-year container plants was feasible for nurseries. Cultivars displayed significantly different growth index throughout the container trial. Fast-growing cultivars, ‘Bullseye’ and ‘Ostbo Red’, grew to over 100 cm, 150 cm, and 250 cm while slower growers like ‘Firecracker’ and ‘Tinkerbell’ had less than 80 cm, 115 cm, and 180 cm in one, two, and four years, respectively. Cultivars were classified into five groups, which were dwarf habit with pink flower, dwarf habit with non-pink flower, non-dwarf habit with green stem and white flower, non-dwarf habit with pigment-patterned flower, and non-dwarf habit with pink flower. This information provided growers on how to select various cultivars for their production among groups. In the field study, performance rating of 21 cultivars ranged from 2.0 to 4.8 (out of 5.0) in 2014 and from 2.0 to 5.0 in 2015 and significant differences were observed in 2014. Ten cultivars received the highest ratings over the two years were selected for the subsequent field trial in 2016. Cultivars showed overall decreased ratings (1.0-3.3) from the previous two years because of late spring planting and relatively unfavorable soil conditions. ‘Ostbo Red’, ‘Pristine’, and “Tinkerbell’ had higher performance rating, more net growth, and less decrease in maximum quantum yield, which indicated their adaptation to the southeastern environmental conditions. Nursery growers and consumers should benefit from our regional cultivar trial information and we recommend ‘Ostbo Red’, ‘Pristine’, and ‘Tinkerbell’ for the southeastern landscapes based on their superior container and field performance, leaf spot resistance, and morphological variations.