Knowledge Bank

Excessive vegetative growth of ornamental grasses presents several production challenges for commercial greenhouse and nursery growers. Prohexadione-calcium, a plant growth regulator (PGR), has been used to reduce growth in a variety of fruit and grain crops. The foliar influence of prohexadione-calcium on five popular and commercially available ornamental grasses was evaluated in this study. Calamagrostis acutiflora ‘Karl Foerster’, Miscanthus sinensis ‘Huron Sunrise’, Panicum virgatum ‘Red Flame’, Pennisetum alopecuroides ‘Hameln’, and Schizachyrium scoparium ‘Twilight Zone’ were sprayed with 0, 500, 1000, 1500, 2000, 2500, 3000, or 5000 mg·L–1 prohexadione-calcium in a completely randomized block design. Each species received one spray application and were evaluated 2, 4, and 6 weeks after application to determine plant height and diameter. After 6 weeks, the experiment was terminated, and plants were excised at the substrate level to determine shoot dry weight. Prohexadione-calcium significantly (P ≤ 0.05) reduced plant height, plant diameter, and shoot dry weight of Miscanthus ‘Huron Sunrise’, compared to the control. Plant height and plant diameter of Schizachyrium ‘Twilight Zone’ was only affected 6 weeks after application and reduced shoot dry weight. While prohexadione-calcium applications on Miscanthus ‘Huron Sunrise’, Panicum ‘Red Flame’ and Pennisetum ‘Hameln’ had minimal to no effect on plant height or plant diameter but varying significance on shoot dry weight. Data from this study suggests that foliar application of prohexadione-calcium on ornamental grasses shows promise but is species- and concentration specific.