Paclobutrazol Inhibits Growth of Zinnia and Geranium

‘Scarlet Ruffles’ zinnia (Zinnia elegans Jacq.) and ‘Smash Hit’ geranium (Pelargonium × hortorum L.H. Bailey) were treated with soil drenches and foliar sprays of paclobutrazol for height control. Single drench applications of 0.5 or 1.0 mg a.i./pot and single spray applications of 250, 500, or 1000 ppm were effective in reducing the height of zinnia. Geranium height was reduced by single drenches of 0.0075 or 0.015 mg a.i./pot and single sprays of 20 or 40 ppm. Higher drench or spray rates resulted in excessive reductions in height and leaf size. Chemical name used: (±)-(R*, R*)-β([4-chlorophenyl]methyl)-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).