Dipping Bedding Plant Liners in Paclobutrazol or Uniconazole Inhibits Subsequent Stem Extension

Abstract

An increasingly popular technique for applying plant growth regulators (PGRs) to floriculture crops is to dip or soak the root medium of a transplant in a chemical solution before transplanting. This PGR application method, termed a “liner dip,” can be an effective height-control strategy for greenhouse crop production. However, few studies have quantified how bedding plant species respond to different chemicals and application rates. Argyranthemum (Argyranthemum ×hybrida ‘Sunlight’), calibrachoa (Calibrachoa ×hybrida ‘Callie Dark Blue’), petunia (Petunia ×hybrida ‘Cascadias Vivid Red’), scaevola (Scaevola albida ‘Jacob's White’), and verbena (Verbena ×hybrida ‘Rapunzel Red’) liners were dipped in paclobutrazol at 4, 8, or 16 mg·L−1 or in uniconazole at 2, 4, or 8 mg·L−1 for 30 seconds and subsequently transplanted into 4.5-inch-diameter round pots. At 28 days after transplant, all rates of paclobutrazol and uniconazole inhibited subsequent stem elongation by 21% to 67% in calibrachoa, petunia, scaevola, and verbena. In argyranthemum, stems were 33% to 42% shorter in plants treated with paclobutrazol at 8 or 16 mg·L−1 or uniconazole at all rates. In some species, the liner dip delayed flowering and reduced flower number compared with that of nontreated plants. This pretransplant PGR application technique can be useful on vigorous ornamental species when grown together in the same container with less aggressive species without a PGR application.