Reducing irrigation applications in container production is necessary for growers to adapt to decreasing water supplies, reduce the environmental impact of production, and comply with a growing number of regulations regarding nursery and greenhouse water use, fertilizer applications, and nutrient levels in runoff (Chappell et al., 2013; Fulcher et al., 2016). However, growers often prefer to overapply rather than underapply irrigation and fertilizer out of concern that lower amounts could negatively affect growth (Million et al., 2007; Owen et al., 2008). Improved knowledge of plant water requirements and more efficient irrigation systems allow plants to be produced with not only RI but also reduced labor, fertilizer, pesticides, growth regulators, and production-related energy inputs (Lichtenberg et al., 2013). There is also a growing preference of consumers for plants produced more sustainably (Behe et al., 2013).
Consumers expect good-quality, uniform, healthy plant material at a reasonable cost (Brand and Leonard, 2001; Guo et al., 2018). Visual appearance is an important consumer quality for ornamental container plants (Brand and Leonard, 2001). Consumers often purchase plants based on the perception that plant health and visual appearance correspond. Uniform growth, leaves on lower branches, dense foliage, leaf color, and bloom quality can all affect the visual appearance and appeal of a plant to consumers (Brand and Leonard, 2001; Glasgow et al., 1998). In a survey of consumers in New England states, the top characteristic they looked for in a retail establishment was “healthy, fresh, and well-maintained plants” (Brand and Leonard, 2001).
Plant quality control can be a large component of container plant production as uneven growth and poor branching may lead to customer rejection of plant material or poor sales (Koniarski and Matysiak, 2013). Lack of uniformity of plant material can result from uneven irrigation distribution, variation in pruning from person to person, or plant growth regulator application variability by species, substrate, and application timing. Hand pruning is also labor intensive, and plant growth regulators will potentially be restricted due to concerns over chemical use in production, necessitating alternative means of growth control (Kaufmann et al., 2000). Reduced irrigation applications can be used as a method of plant growth control and to improve crop quality (Koniarski and Matysiak, 2013); however, this requires knowledge of species-specific water requirements and uniform irrigation applications. Too little water can result in reduced leaf size, short internodes, reductions in flower size, fewer flowers, and an overall reduction in plant quality (Sánchez-Blanco et al., 2002). Conversely, undesirable plant growth, including excessive growth, long internodes, and large variation in leaf size, can result from overapplication of water and fertilizer (Koniarski and Matysiak, 2013). Plants with uneven growth are less likely to sell in a retail setting and may require additional labor and resources to improve salability. Water stress during shipping and while in a retail setting can also result in unsalable plants due to reduced visual appeal (Hall et al., 2011). Another benefit of deficit irrigation is the potential to help plants gain tolerance to drought stress conditions that may be encountered during shipping, in a retail nursery, or in a home landscape setting (Cameron et al., 2008; Guo et al., 2018).
The production of more compact plants could also influence shipping costs (Burnett and van Iersel, 2008). Container plants are often stacked or racked during shipping (Eaton and Appleton, 2014), meaning smaller, more compact plants create the potential to fit more plants on a truck. It is beneficial to both producers and consumers if more plants can fit onto a truck because it helps distribute shipping costs onto more plants.
Sensor-controlled irrigation studies have shown the relationship between plant growth and substrate volumetric water content (VWC) threshold for many ornamental plants, including ‘Panama Red’ hibiscus (Hibiscus acetosella), gardenia (Gardenia jasminoides), lantana (Lantana camara) ‘Siskiyou Pink’ gaura (Gaura lindheimeri), ‘Mini Penny’ hydrangea (Hydrangea macrophylla), rosemary (Rosmarinus officinalis), canadian columbine (Aquilegia canadensis), and ‘Bath’s Pink’ cheddar pinks (Dianthus gratianopolitanus) (Bayer et al., 2013, 2014, 2015; Burnett and van Iersel, 2008; van Iersel et al., 2009; Zhen et al., 2014). The timing of deficit irrigation applications has been reported to affect flower bud development along with controlling plant growth. Flowering has been either promoted or inhibited depending on the species and degree of water stress (Álvarez et al., 2009, 2013; Cameron et al., 1999; Koniarski and Matysiak, 2013; Sharp et al., 2009). More information is needed on the timing of deficit irrigation applications on the growth and flowering of ornamental species to best use this method. The objective of this study was to determine the effectiveness of RI timing on growth, flowering, and quality of the popular herbaceous perennials coneflower and sneezeweed.
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