In some species of bedding plants, rapid hypocotyl elongation during germination makes size control in plug production difficult. Commercial growers often start applying growth regulators as cotyledons are expanding or after the first true-leaves are expanding. Using `Bonanza Spry' marigolds, we evaluated applying paclobutrazol at sowing and after 3 and 6 days. Sprays at 30 mg·L–1 in a volume of 0.2 L·m–2 or 3 mg·L–1 in 0.6 mg·L–1 applied at sowing reduced hypocotyl elongation by 25% and produced more compact plugs. In a second study, plugs of `Double Madness Rose' petunia, `Showstopper Orange' impatiens, `Wizard Rose' coleus, and `Cooler Rose' vinca were grown in 10-cm pots with a growing medium that did not contain pine bark. Uniconazole was sprayed in a volume of 0.2 L·m–2 onto the surface of the medium before planting at concentrations of 25%, 50%, and 100% of the label's recommended concentration for each crop. An additional treatment was uniconazol applied 2 weeks after planting at the label concentration. All early applications reduced final plant size compared to the nonsprayed plants. For impatiens, the early application at 25% of the label concentration produced plants similar to the spray at 2 weeks after planting. For the other crops, the 50% treatment prodcued plants similar to the spray after planting. The early applicaiton of growth regulators offers the industry an additional stradagy to use for controlling the growth of vigorous bedding plant crops.
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