Controlling height of bedding plants can be one of the most difficult challenges for commercial greenhouse growers. Plant growth regulators (PGRs) often are used to inhibit stem elongation and to limit final plant height. Several techniques are commonly used to apply growth-regulating chemicals, including a foliar spray, a substrate drench, or a combination of both (i.e., sprench) (Barrett, 1999). For bulbous crops, such as hyacinth (Hyacinthus orientalis) or ‘Star Gazer’ oriental lily (Lilium hybrids), a preplanting bulb soak in a PGR solution is an effective height-control strategy (Krug et al., 2005, 2006). An application method that has become increasingly popular among commercial growers is to dip or soak the root medium of a transplant in a chemical solution before transplanting (Schnelle et al., 2005). This PGR application method is termed a “liner dip” or “liner soak” (Schnelle et al., 2005). Advantages of a liner dip include ease of application, effectiveness in controlling stem elongation of aggressive species, ability to treat a large number of plants before transplanting into a final container, and reduced chemical runoff during application. In addition, a liner dip can be an effective application method when using chemicals such as paclobutrazol or uniconazole, which are absorbed by roots and transported in the xylem (Davis et al., 1988).
A pretransplant liner dip has been reported to inhibit stem elongation in potted plants and herbaceous perennials. In poinsettia (Euphorbia pulcherrima), soaking foam strips in a solution of uniconazole at 1.0 mg·L−1 for 15 min before transplanting suppressed plant height by 55% compared with that of nontreated plants (Bearce and Singha, 1992). Latimer and Groover (2005) reported that Russian sage (Perovskia atriplicifolia) liners dipped in a solution of paclobutrazol at 2.0 mg·L−1 or uniconazole at 1.0 mg·L−1 for 15 min before transplant were 26% or 35% shorter than nontreated plants respectively at 5 weeks after application. These studies indicate that greenhouse growers can use a PGR liner dip to control the height of some greenhouse crops. However, more research information is needed to determine the response of other species to different chemicals and application rates. The objective of this study was to determine the effects of a pretransplant liner dip application of paclobutrazol and uniconazole on five common species of bedding plants.
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