Across the United States, growers have developed local, niche markets for specialty cut flower crops that are in demand by U.S. consumers for their unique blooms and fresh quality (Armitage and Laushman, 2003). Stems are typically sold wholesale to local retail businesses, such as florists, or as prearranged bouquets in direct markets, such as farmers markets, farm stands, and community-supported agriculture subscriptions (Connolly and McCracken, 2016). These markets, combined with increasing public demand for local agricultural products (Wolfe and McKissick, 2007; Yue et al., 2011; Zongyu et al., 2016), have led to an increase in cut flower farms across the U.S. national membership in the Association of Specialty Cut Flower Growers (ASCFG) reflects this: there are now 1980 members (Judy Laushman, personal communication, 21 Aug. 2020), a quadrupling in membership since 2008. Included in this growth are nontraditional regions for cut flower production, such as the U.S. Intermountain West, where 86 small-scale farms have been established in Utah and southern Idaho, as well as a Utah-based cut flower farmer association that gained 114 members since launching in mid-2019 (Utah Cut Flower Farm Association, 2021).
Local trials are critical for optimizing cut flower production against regional constraints (Ortiz et al., 2012; Wien, 2009). Surveys of growers emphasize this need with season extension, control of bloom timing, and cultivar selection as the top-ranked regional research priorities in a survey conducted at the 2019 Utah Urban and Small Farms Conference (Cut Flower Growers Survey, 20 Feb. 2019), and season extension and control of bloom timing were top needs across the United States and Canada (Loyola et al., 2019). Growing in a low-cost high tunnel can advance and increase production by stabilizing environmental conditions (Lamont, 2009; Wells and Loy, 1993), particularly for cool-season crops. Passive heating advances planting and harvest to meet early market demands (Starman et al., 1995; Wien, 2009). High tunnels also offer physical protection from late snowstorms and rainfall that can damage the crop (Lamont, 2009; Wien, 2009). Later in the growing season, high tunnels can be transformed into shade structures by replacing the plastic film covering with shadecloth to reduce temperature and solar radiation (Wien, 2009). For cut flower production, shade may have additional benefits, such as increasing stem length, and hence marketable yields (Armitage, 1991).
Snapdragons (Antirrhinum majus) are a cool-season crop that florists have indicated interest in regularly sourcing from local growers (Wolfe and McKissick, 2007). Although pricing varies by stem length grade and daily demand throughout the year, typical wholesale prices per 10-stem bunch ranged from $8.50 to $10.00 for short and medium stem lengths and $12.00 to $15.00 for long and extralong lengths (USDA Agricultural Marketing Service, 2019). Local wholesalers have indicated that there is a preference for stems of 92-cm length, which are shipped upright to prevent stem curvature (Roger Callister, personal communication, 22 Mar. 2021). Therefore, farm revenues may be increased with production practices that can consistently supply longer stems, stored upright, over a greater window of time.
Key factors influencing snapdragon stem length and bloom timing are daylength and temperature. As quantitative long day plants (Armitage and Laushman, 2003; Owen et al., 2018), snapdragons will flower under short days, but days to flowering decreases as the daylength and light intensity increases (Adams et al., 2003; Cremer et al., 1998; Warner and Erwin, 2005). However, as light duration and intensity increase, stem length decreases (Gutierrez, 2003). The optimal temperature range for snapdragons is 7 to 18 °C and varies by cultivar (Armitage and Laushman, 2003), which are grouped I through IV, according to flower initiation response to temperature, daylength, and light intensity (Dole and Wilkins, 1999; Larson, 1992). Group I–II cultivars, such as ‘Chantilly’, bloom the earliest under shorter days and require minimum temperatures of 7 to 13 °C (Armitage and Laushman, 2003; Dole and Wilkins, 1999) with 6.2 to 18.6 MJ·m−2·d−1 (Ball Horticulture, 2011), whereas ‘Potomac’ (Group III–IV) and ‘Rocket’ (Group IV) bloom the latest and require nighttime temperatures of 13 to 16 °C, longer daylength, (Armitage and Laushman, 2003; Dole and Wilkins, 1999) with 15 to 31 MJ·m−2·d−1 (Ball Horticulture, 2021). Across cultivars, the maximum temperature is 31 °C (Runkle, 2010), indicating an adaptability to lower temperature and light conditions as a cool-season crop.
On the basis of these growth requirements, snapdragons have strong production potential in the U.S. Intermountain West, and trials in the U.S. Midwest and Southeast help establish baseline transplant dates, harvest timing, and yield. In a field trial in Tennessee (USDA-ARS, 2012; USDA Hardiness Zone 7a), ‘Rocket Bronze’, ‘Rocket Pink’, and ‘Rocket White’ (Group IV) were transplanted 5 May and began blooming in early June (Starman et al., 1995). The total yield averaged 16 to 30 stems per plant (112 to 210 stems/m2) and 36 to 45 cm stem lengths which (Starman et al., 1995). Some researchers have used a grading standard of 30 to 41 cm for marketable stems (Kluza, J. 2019; Ortiz, et al., 2012: Owen, et al., 2016; Starman, et al., 1995), whereas others have used 46 cm as the grading minimum for marketable stems according to the Society of American Florists (Carter and Grieve, 2008; Dole and Wilkins, 1999; Miller, 1961). In Indiana [USDA Hardiness Zone 5b; USDA Agricultural Research Service (ARS), 2012], ‘Rocket Red’ (Group IV) was planted on 16 and 17 May, 1 week after the last frost date; this yielded an average of 183 stems per m2 and 51.8 cm stem lengths in the high tunnel, and 158 stems per m2 and 39 cm in the field, indicating that high tunnels can significantly increase both production quantity and quality (Ortiz et al., 2012). In North Dakota (USDA Hardiness Zones 3b to 4a, USDA-ARS, 2012), a mix of ‘Rocket’ varieties and ‘Potomac White’ were planted 20 May through 10 June 2016 and 24 April through 2 June 2017 (Kluza, 2019), up to 7 weeks before the last frost date (North Dakota State University, 2016). These early plantings yielded an average of 241 stems per m2 with 43 cm stem lengths in the high tunnel and 120 stems per m2 with 30 cm stem lengths in the field (Kluza, 2019). Although high tunnel use (Kluza, 2019; Ortiz et al., 2012; Starman et al., 1995), cultivar selection (Kluza, 2019; Ortiz et al., 2012; Starman et al., 1995; Wien, 2013), and multiple transplanting dates (Kluza, 2019) have been explored independently, testing combinations of I–II and III–IV groups with staggered transplant dates under high tunnel and field production systems have not been evaluated and may further increase production and extend the harvest season.
To promote stem elongation during late spring and provide summer production, shadecloth may be used to reduce light intensity, but this may increase time to flowering (Armitage, 1991; Li et al., 2017; Wien, 2009). Compared with an unshaded control, snapdragon stem lengths were 2 cm longer under 30% shade and 17 cm longer under 60% shade (Alhajhoj and Munir, 2016). However, compared with the unshaded control, 30% shade delayed flowering by 7 d and 60% shade delayed flowering by 39 d (Alhajhoj and Munir, 2016). These trials were conducted in Al-Ahsa, Saudi Arabia, where average solar radiation ranges 19.6 to 25.3 MJ·m−2·d−1 during March through July (Alhajhoj and Munir, 2016), compared with 13.7 to 29.1 MJ·m−2·d−1 in northern Utah (Logan, UT) (Utah Climate Center, 2020a). In Starkville, MS, where average solar radiation ranges 14.9 to 21.3 MJ·m−2·d−1 in March through July (Delta Agricultural Weather Center, 2021), the stem length of ‘Potomac Red’ significantly increased from 86.2 cm in full sun to 98.9 cm under 50% shade for the first spring harvest (Li et al., 2017). However, shade delayed springtime harvests by 1 week, stem length was not significantly different from unshaded controls in subsequent harvests, nor was there a significant difference in total yield per plant (Li et al., 2017), indicating a trade-off for using shade to maximize stem length of initial yields.
The use of high tunnels with field production, multiple snapdragon cultivar groups at staggered transplant timings, and shading could result in greater yields with improved stem quality for an extended growing season. Therefore, the objectives of this study were to 1) evaluate high tunnel and field production practices on snapdragon bloom timing, yield, and quality; 2) trial snapdragon cultivars across groups, including ‘Chantilly’ (I), ‘Potomac’ (III–IV), and ‘Rocket’ (IV), for both their productivity in the U.S. Intermountain Mountain West and ability to stagger production; and 3) determine optimal transplant timings to lengthen the harvest season and produce a high-quality crop.
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