Over the past decade, the United States herbaceous perennial sector, including garden chrysanthemum (Chrysanthemum ×morifolium Ramat.) and hosta (Hosta Tratt. sp.) categories, increased by 43% from 2005 to 2015 (USDA, 2006, 2016). To meet this increasing consumer demand for herbaceous perennials, producers must optimize production inputs, understand environmental and cultural requirements, and minimize waste, thereby, consistently producing high-quality flowering crops. However, much of the literature available to perennial growers were established from research that occurred in the late 1990s to early 2000s and included propagation (Enfield, 2002), cold hardiness and overwintering [acclimation, freezing, and deacclimation (Herrick and Perry, 1997; Kingsley-Richards and Perry, 2011; Perry, 2011)], and forcing [vernalization, photoperiod, and temperature (Heins et al., 2000)] studies. Since then, new and ongoing herbaceous perennial research has surfaced including, propagation (Owen, 2017) and plant growth control (Latimer, 2016) studies, respectively.
To date, optimum fertilization requirements (Owen et al., 2013; Scoggins, 2005) and nutritional leaf tissue sufficiency ranges and standards (Barnes, 2010; Biernbaum and Morrison, 2000; Bryson and Mills, 2014; Dole and Wilkins, 2005; Zheng and Clark, 2013) of some herbaceous perennials have been reported. The largest collection of nutritional leaf tissue standards was established by Bryson and Mills (2014), but only 69% of the herbaceous perennial genera reported had tissue samples that represent container-grown plants in greenhouse or nursery production. These published leaf tissue nutritional standards established for container-grown herbaceous perennials represent survey measurements, which provide a wide variability of recommended nutrient levels. Although more than half of the herbaceous perennial leaf tissue nutritional standards represent plants grown in containers, other perennial genera tissue samples were collected from plants grown in mineral soils located in botanical gardens, arboretums, experimental plots, or were field-grown (Bryson and Mills, 2014). Therefore, these nutritional standards do not accurately represent the nutritional status nor sufficiency ranges of herbaceous perennials grown by commercial operations in soilless substrates.
Little attention has been given to identifying nutrient requirements and nutritional status of container-grown plants as related to plant age or stage of development (Tolman et al., 1990). For instance, Bryson and Mills (2014) reported an estimated age and where the leaf tissue was sampled by stating “mature leaves from new growth,” while Campbell (2000) only reported leaf tissue standards for poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) at “all growth stages.” However, for economically significant agronomic crops, such as corn (Zea mays L.), leaf nutrient sufficiency ranges were documented at the seedling (<4 inches), early growth (>4 inches to tasseling), tasseling/bloom, and maturity developmental stages (Campbell, 2000). In annual bedding plants, leaf tissue nutrient sufficiency ranges by chronological age have been reported for pot gerbera (Gerbera jamesonii Bolus ex Hook. f. ‘Festival Light Eye Yellow’; Jeong et al., 2009), osteospermum (Osteospermum hybrida L. ‘Lemon Symphony’, ‘Serenity Lavender Dark’, ‘Summertime Red Velvet’, and ‘Tradewinds Purple Bicolor’; Papineau and Krug, 2014), and zonal geranium (Pelargonium ×hortorum L.H. Bailey ‘Tango Dark Red’ and ‘Rocky Mountain Dark Red’; Krug et al., 2010). Determining sufficiency ranges and leaf nutritional standards by chronological age for herbaceous perennials will establish nutrient recommendations that may aid in identifying nutritional deficiencies, toxicities or both. In addition, reporting of such information will establish optimal fertilizer recommendations. This is significant for commercial production because perennial growers provide plants anywhere from 50 to 700 mg·L−1 N (Pilon, 2006). Established fertilizer recommendations will enable the potential avoidance of excess fertilization, leaching, and runoff contamination from container-grown herbaceous perennials in greenhouses or nurseries.
Thus, there is a need to establish optimum fertilization concentrations and expand leaf tissue nutritional standards for successful herbaceous perennial production. There is little information available regarding optimum fertility requirements for container-grown herbaceous perennials. Established leaf tissue nutritional standards are limited to only 73 herbaceous perennial genera grown in containers (Bryson and Mills, 2014), and to date, herbaceous perennial leaf tissue nutritional sufficiency ranges by chronological age have not been reported. Therefore, the objectives of this study were to determine the optimum fertilizer concentrations, identify leaf tissue nutrient sufficiency ranges by chronological age, and to expand leaf tissue nutrient standards of H. hybrid L. (hibiscus) grown in soilless substrates during container production. Hibiscus served as a model crop because to date, no leaf tissue concentration limits are published for H. hybrid, but only survey measurements taken from greenhouse- and nursery-grown hibiscus species are reported by Bryson and Mills (2014).
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