The wholesale value of floriculture crops in the United States exceeded $5.87 billion in 2014 (U.S. Department of Agriculture, 2015), of which ≈44% ($2.56 billion) was attributed to annual bedding and garden plants. Unlike food-crop producers, for whom fruit or plant biomass production is the primary objective, the goal of bedding-plant producers is to grow plants that have high-quality aesthetics. Commercial bedding-plant producers often grow a diverse range of species in common environments which present challenges, as plants respond differently to environmental conditions and cultural factors (Andersson, 2011; Blanchard and Runkle, 2011).
To produce plants of acceptable size and quality, bedding-plant producers manipulate environmental parameters such as light and temperature (Erwin et al., 1989; Faust et al., 2005) or use crop culture practices such as withholding water (Alem et al., 2016) or changing mineral nutrient source, concentration, or delivery system (Klock-Moore and Broschat, 2001) to control growth. However, providing species-specific cultural practices can be challenging in production environments containing many species and may not be practical or feasible depending on the facility and available equipment. Plant growth retardants are frequently used in bedding-plant production to restrict growth of plants, as they can be easily applied without adversely affecting other crops in the same environment.
Plant growth retardants are often applied as foliar sprays, but research has shown that longer term growth restriction and more uniform control can be achieved when they are applied as substrate drenches (Boldt, 2008; Gent and McAvoy, 2000; Whipker et al., 2006). As a result, PGR drench applications are a preferred method among many producers (Owen et al., 2016). Efficacy of PGR applications can be affected by plant genetics (Currey et al., 2016b), active ingredient (Currey et al., 2016a), application method (Hawkins et al., 2015), and, in the case of substrate drenches, substrate components (Barrett, 1982; Bonaminio and Larson, 1978; Currey et al., 2010). Substrate components such as pine (Pinus sp.) bark can reduce the efficacy of PGR drenches (Bonaminio and Larson, 1978), whereas the presence of parboiled rice (Oryza sativa) hulls in substrate does not (Currey et al., 2010).
Biocontainers, which provide an alternative to petroleum plastic plant containers, can be manufactured from a variety of organic parent materials and vary in both physical and chemical properties (Conneway et al., 2015; Evans et al., 2010; Grewell et al., 2014). With new biocontainers entering the commercial market, including some bioplastic containers that release supplemental nutrients as they degrade (Currey et al., 2014, 2015; Schrader et al., 2013) and other biocontainer types whose physical properties influence plant growth by reducing available water to plants (Evans and Hensley, 2004; Evans et al., 2010), we hypothesized that some biocontainer types may influence PGR drench efficacy. We have found no previous research that investigates this potential interaction. Therefore, our objectives were to determine the effects of different types of biocontainers on the efficacy of paclobutrazol substrate drench when using a variety of commercially available biocontainers and two novel bioplastic-based containers.
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