Use of Growth Retardants to Promote Flowering of Mountain Laurel, Kalmia latifolia L.

Abstract

Abstract Spray treatments of the growth retardants A-Rest (ancymidol at 0, 53, 106 ppm), Bonzi (paclobutrazol at 0, 10, 50, 100, 200, 400, 600 ppm) and Sumagic (uniconazole at 0, 10, 25, 50, 75, 100, 200, 300 ppm) were applied to container-grown Mountain laurel (Kalmia latifolia L.) to evaluate their effectiveness for promotion of flower initiation and inhibition of shoot elongation. A-Rest had no effect on flower initiation at the concentrations tested. Bonzi promoted a moderate increase in inflorescences on one cultivar evaluated. Uniconazole sprays of 50 ppm or higher increased inflorescence numbers of most cultivars tested. Application in the spring to plants two years from propagation gave the most consistent results, however, with some cultivars, applications following the second growth flush as late as early August promoted flower initiation. Uniconazole treatments also reduced stem elongation resulting in more compact growth. Stem elongation was retarded with increasing concentrations of uniconazole for the growth flush in the spring in the year following treatment. The results of this study show that Sumagic (uniconazole) in the range of 50 to 75 ppm increases inflorescence numbers without excessive growth inhibition when applied in the spring to most cultivars two years from propagation.