Chemical Regulation of Growth of Perennial Bedding Plants

in HortScience
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  • 1 215 Hoke Smith, Dept. of Horticulture, Univ. of Georgia, Athens, GA 30602

Perennial growers experience marketing difficulty when the stem length, or height of their perennial stock is excessive. Both wholesale and retail outlets desire to keep height to a minimum, while still promoting the production of flowers. The objective of this study was to screen containerized, spring-planted perennials for response to the growth retardants Sumagic, Bonzi, and B-Nine. Each perennial variety used was treated with B-Nine (Daminozide at 5000 ppm Bonzi (paclobutrazol) at 240 ppm, and Sumagic (uniconizole-P) at the following rates: 0, 40, 80, 120, and 160 ppm.Pre-cooled plugs of cultivars were selected from the genera Achillea, Coreopsis, Echinaceae, Digitalis, Gaillardia, Phlox, Rudbeckia, Alcea, Veronica, and Monarda. A randomized complete block design was implemented. Eight of the nine cultivars were responsive to Sumagic, with a 12% to 79% range of reduction in height. Seven cultivars were responsive to Bonzi with a 20% to 61% range of reduction. Only one cultivar was responsive to B-Nine, requiring two applications of 5000 ppm, to yield a 22% reduction in height at 4WAT. Based upon growers' desire for up to 50% height reduction, a 30% height reduction assessment point was established as a minimum rate for production, and a 50% to 60% reduction was established as the maximum landscape rate (based upon in-landscape persistence).