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Article

Overwintering Improves Ranunculus Cut Flower Production in the US Intermountain West

by
Shannon Rauter
1,*,
Melanie Stock
1,
Brent Black
1,
Dan Drost
1,
Xin Dai
2 and
Ruby Ward
3
1
Department of Plants, Soils and Climate, Utah State University, 4820 Old Main Hill, Logan, UT 84322, USA
2
Utah Agricultural Experiment Station, Utah State University, 4810 Old Main Hill, Logan, UT 84322, USA
3
Department of Applied Economics, Utah State University, 4835 Old Main Hill, Logan, UT 84322, USA
*
Author to whom correspondence should be addressed.
Horticulturae 2022, 8(12), 1128; https://doi.org/10.3390/horticulturae8121128
Submission received: 31 October 2022 / Revised: 23 November 2022 / Accepted: 29 November 2022 / Published: 1 December 2022
(This article belongs to the Section Floriculture, Nursery and Landscape, and Turf)
Browse Figures
Review Reports Versions Notes

Abstract

:
Ranunculus (Ranunculus asiaticus L.) cut flower production in the US Intermountain West is limited by a narrow window of optimal temperature ranges in the spring. With the increasing number of Intermountain West cut flower growers, regional management recommendations are needed to improve ranunculus harvest timing and yield. The objectives of this research were to evaluate planting dates, winter insulation, tuberous root (TR) preparation, and cultivar selection for flower timing, yield, quality, and profitability in high tunnel and field production systems. Trials were conducted in a North Logan, UT (41.7665° N, −111.811° W, 1405 m elevation, USDA hardiness zone 5) high tunnel and field from fall 2019 to spring 2022. TRs were either pre-sprouted or directly planted into a high tunnel (left bare or covered with low tunnels) or field (left bare or covered with mulch, a low tunnel, or mulch and a low tunnel) from November to April. High tunnels advanced production by four weeks, nearly doubled total yield, and increased the proportion of quality (longer than 25 cm) stems by 50% compared to the field. Planting pre-sprouted TRs in the high tunnel in November delivered the earliest harvest (6 Apr.), highest marketable yield (286 stems per m2 ± 36 SE), and highest net returns ($54 per m2), with 39% greater marketable yield for ‘LaBelle’ than ‘Amandine.’ Insulation nearly doubled emergence and improved marketable yield by 49 stems per m2 ± 8 SE for November field plantings. Ranunculus production was optimized as a fall-planted high tunnel crop in the Intermountain West but may be fall-planted in the field with insulation, allowing growers to maximize production during more optimal, early-season temperatures.

1. Introduction

Approximately 80% of cut flowers consumed in the US are imported, mainly from South American countries and the Netherlands [1]. Domestic industry has adapted to increases in inexpensive floral imports by focusing on production of specialty flowers with short vase lives or that lose quality during shipping [2]. Small-scale, domestic flower farmers typically sell stems wholesale to local florists or take advantage of direct markets in the form of farmers markets, community supported agriculture (CSA), and you-pick operations [3,4]. National membership in the Association of Specialty Cut Flower Growers has approximately quadrupled since 2008, to nearly 3000 members in 2022 [5]. In the Intermountain West region of the US (Utah, Idaho, Nevada, western Colorado), cut flower farming is a rapidly growing niche industry that attracts consumers with ‘farm to vase’ social media marketing strategies. Since its launch in 2019, the Utah Cut Flower Farm Association (UCFFA) has gained 145 members [6].
Ranunculus (Ranunculus asiaticus L.) is an economically important crop in the global cut flower industry that was produced by 44.7% of 188 cut flower growers surveyed in the U.S. and Canada in 2017 [1,7]. Yields of ranunculus typically range from three to six stems per plant, but high tunnel yields up to 12 stems per plant have been reported with stem lengths ranging from 20 to 50 cm [2,8,9,10]. In 2021, the price for one bunch of ten ranunculus stems ranged from $12.50 to $26.00 at the Boston terminal market and $12.00 to $17.00 in Northern Utah, with prices varying by country of import, month, and stem length [11,12]. Ranunculus is a promising specialty cut flower crop for small growers because of its low space requirements and high profit potential, but Intermountain West growers require regionally specific recommendations to maximize yields, as many management recommendations originate in milder climates [13,14].
As cool season, tender perennials, ranunculus concentrate growth and flowering when the weather is cool and wet, making production in the US Intermountain West difficult because optimum temperature ranges for production occur over a narrow window in the spring [15,16]. Ranunculus are typically forced from tuberous roots (TRs) that are replaced annually for small farm production and flower approximately three months after planting [1]. Grower resources advise fall planting for ranunculus in USDA hardiness zones 7 and above, and spring planting for USDA hardiness zones 6 and below [2,17], but these recommendations, based on air temperature, may be poor hardiness indicators for bulbous plants that are responding to soil temperature prior to emergence [18]. The freeze tolerance of ranunculus TRs is directly linked to their moisture level, with a minimum survival threshold of −2 to −4 °C for hydrated TRs (80–90% water content) [18,19,20,21].
While fall planting is not recommended for Northern Utah (USDA hardiness zone 5) because of the risk of cold injury, spring plantings are limited by early summer heat. If ranunculus plants can overwinter, fall planting could improve harvest duration and quality by shifting harvest to a period of cooler temperatures. The optimum temperature range for growth and flowering of ranunculus plants is between 7 to 9 °C at night and 14 to 18 °C during the day [1]. Above their upper temperature threshold of 21 to 25 °C, the plants stop flowering, prioritize TR development, and enter dormancy [1,16,22]. Concentrating ranunculus production when air temperatures range from 7 to 18 °C, without risk of the soil reaching −2 °C or the air reaching 25 °C, will help Intermountain West growers maximize production. In Northern Utah, this optimal temperature window typically occurs from March to May [23]. Additionally, as the growing season progresses toward mid-summer, insect and weed pressure increase, demand for cool-season cut flowers decreases [2,24], and water availability can limit production [25], highlighting additional benefits to advancing harvest as early as possible. Fall planting; the use of various insulation options, such as high tunnels, low tunnels, and mulch; pre-sprouting TRs rather than direct planting; and cultivar selection are potential ways to advance the growing season and optimize flower timing, quality, and marketable yield.
High tunnels are temporary structures that are passively heated and cooled to extend optimal growing conditions [26]. High tunnels have potential to protect fall-planted TRs from below-freezing winter temperatures and allow for winter planting by excluding snow and limiting frozen ground [10,27,28]. High tunnels may also benefit cut flower growers by extending the growing season by up to two months and improving yield and stem lengths compared to field production [29,30,31]. Although high tunnels can benefit cut flower production, most Utah cut flower farms are considered micro farms and may not have enough space to install a high tunnel, limiting many growers to field production [32]. Low tunnels and mulches, such as straw, present an opportunity to insulate fall-planted TRs from subfreezing temperatures for growers with space limitations, and reduce costs compared to high tunnel production [18,27,33]. In a Minnesota trial (USDA hardiness zone 4), ranunculus species mulched with 10 cm of hay survived the winter, while those without mulch did not [18], indicating that insulation can be used to modify soil temperature and improve the overwintering ability of ranunculus.
Flower timing is also impacted by cultivar and TR preparation, with some cultivars marketed as more cold-tolerant (e.g., ‘LaBelle’) or heat-tolerant (e.g., ‘Amandine’) and recommended for earlier or later plantings, respectively [34]. Dry ranunculus TRs are typically soaked for 3 to 36 h to rehydrate before planting [13,16,35]. After soaking, some resources recommend pre-sprouting, by starting TRs in a growing medium at a cool temperature for multiple weeks before planting, to achieve flowers 3 to 4 weeks earlier than non-pre-sprouted TRs [2,13]. Two to four weeks at 5 to 6 °C hastened ranunculus flowering but reduced total yield in a Japanese greenhouse study [35], while three weeks at 10 °C improved winter survival of ranunculus in a New York high tunnel and did not significantly impact yield [36]. Other recommendations for pre-sprouting ranunculus vary from 2 to 4 weeks at 2 to 5 °C [35,37,38] to 4 to 5 weeks at 4 to 10 °C [2,38]. With the inconsistencies in recommended pre-sprouting requirements, additional exploration is needed to create recommendations for growers that can deliver consistent results in harvest timing and yield.
The objective of this study was to evaluate ranunculus emergence, flower timing, yield, and quality by (1) fall versus spring planting dates; (2) combinations of the winter insulation methods of high tunnels, low tunnels, and straw mulch; (3) pre-sprouting tubers before planting versus direct planting; and (4) cultivar. We hypothesized that pre-sprouting, fall planting, and insulating TRs increase ranunculus yield and quality by advancing growth and production during more optimal, early-season temperatures.

2. Materials and Methods

Field and high tunnel trials were conducted at the Utah Agricultural Experiment Station Greenville Research Farm in North Logan, UT (lat. 41.77° N, long. 111.81° W, 1382 m elevation, 135 freeze-free days, an average last frost date on 15 May, and USDA hardiness zone 5). The soil is a Millville silt loam with 2% organic matter [39].
In 2019–20, a preliminary field trial consisted of two, 1.2 mW × 7.7 mL beds, each subdivided into three, 3.1 m2 plots in a randomized complete block design. Three winter insulation treatments were tested to establish baseline winter soil temperature dynamics: bare soil (-LT-M), mulch only (-LT+M), and a low tunnel with mulch (+LT+M). Survival, crop timing, and production were tested with -LT-M and +LT+M, with 19 Nov., 9 Mar., and 3 Apr. planting dates for two cultivars (‘Amandine’ and ‘LaBelle’). In 2020–21 and 2021–22, the field study expanded, consisting of three, 1.2 mW × 12.2 mL beds, each subdivided into four, 3.7 m2 plots. Four insulation treatments were randomly assigned to whole plots: low tunnel with mulch (+LT+M), low tunnel only (+LT-M), mulch only (-LT+M), and bare soil (-LT-M). Whole plots were divided into three subsections and randomly assigned a planting date (15 to 18 Nov., 17 to 23 Mar., and 16 to 18 Apr.), while rows within each subsection were assigned a cultivar (‘Amandine’ and ‘LaBelle’) and a pre-sprouting treatment (pre-sprouted [+PS] and non-pre-sprouted [-PS]).
One, 4.3 mW × 12.8 mL high tunnel [40] oriented east–west was subdivided into six, 4.4 m2 plots, organized in a randomized complete block design from 2019 to 2022. The addition (+LT) and absence of a low tunnel (-LT) were tested in triplicate at the whole plot level with a subplot treatment factor of pre-sprouting (+PS and -PS), except in 2019–20 when pre-sprouting was not tested. Within subplots, the treatment factors of planting date (16 to 21 Nov., 14 to 18 Jan., 7 to 17 Feb., and 6 to 17 Mar.) and cultivar (‘Amandine’ and ‘LaBelle’) were tested, except in 2019–20 when no January planting date was tested.
The high tunnel and field were rototilled before planting in November each year. Phosphorus (P, guaranteed analysis 0N-20P-0K) and Potassium (K, 0-0-50) fertilizer applications were based on soil test results, and Nitrogen (N) fertilizer (46-0-0) was incorporated as a split application at a rate of 73 kg N ha−1 in November and again in spring when flower buds were visible. Color mixes of ranunculus ‘Amandine’ and ‘LaBelle’ (size 5–7 cm) TRs (Ball Horticulture, Chicago, IL, USA) were soaked for 3 to 4 h in 15 to 25 °C running tap water for aeration [41]. In the last 20 min. of soaking, the TRs were drained and placed in a solution of 0.3% Captan fungicide to reduce risk of rot [41]. To pre-sprout, soaked TRs were placed in flats with a moist soilless growing medium consisting of 68% peat moss (Canadian sphagnum peat moss; Sun Gro Horticulture, Agawam, MA, USA), 32% vermiculite (Therm-O-Rock West, Chandler, AZ, USA), 0.48 g·L−1 AquaGro 2000 G (Aquatrols, Paulsboro, NJ, USA), and 1.43 g·L−1 hydrated lime (Ca(OH)2; Mississippi Lime, St. Louis, MO, USA). The pre-sprouted TRs were kept at a day/night temperature regime of 22/18 °C for one week and then at an average temperature of 11.7 °C for an additional week to acclimate to cooler temperatures. TRs were planted 0.15 m apart within and between rows at a depth of 0.05 m, and drip tape (Aqua-Traxx, Toro, Bloomington, MN, USA) was used to irrigate zero to three times per week, depending on environmental demand.
Throughout the season, high tunnel temperatures were managed by manually venting the structure based on field weather conditions reported from an automatic weather station located 0.2 km away [23] according to [29]. Low tunnels in the high tunnel and field were covered with fabric row cover (AG-50, 50.6 g·m−2, Arbico Organics, Oro Valley, AZ, USA), and manually vented when ambient air temperature was over 15 °C [32]. Mulch consisted of approximately 0.1 m of straw placed on the soil surface (approximately 2 kg·m−2). Based on air temperature monitoring, mulch was removed between 1 and 15 Mar., low tunnels were removed between 8 Mar. and 11 May, field plots were shaded between 23 Apr. and 11 May, and high tunnel plastic was replaced with shade between 5 and 13 May each year.
In 2019–20, one sensor (HOBO MX2200 Series Pendant, Omega Engineering, Norwalk, CT, USA) recorded soil temperature at a 0.05 m depth in each high tunnel and field plot, and air temperature (2.0 m height) was measured at the Greenville weather station [23]. In 2020–21 and 2021–22, one soil temperature and moisture sensor (True-TDR-315H, Acclima, Inc., Meridian, ID, USA) was installed at a 0.05 m depth in one replicate per field insulation treatment and three replicates per high tunnel insulation treatment. A shielded thermistor (CS 107, Campbell Scientific, Logan, UT, USA) measured air temperature at 0.25 m in one replicate per field and high tunnel insulation treatment. Data were recorded at one-minute intervals with data loggers (CR-1000, Campbell Scientific) and multiplexers (AM25T, Campbell Scientific) to calculate hourly and daily averages. From 2019 to 2022, precipitation was measured at the Utah State University campus approximately 3 km from the trial [42].
Plant emergence was counted weekly from planting until harvest. Harvest occurred three to four times per week and stems were cut when fully colored at the loose bud stage [43]. Stems were graded by length and quality per market preferences, pricing, and seasonality, as reported from local farms. ‘Quality’ grade stems were at least 25 cm in length, free of curvature or visual deformities, and sold for $15 per bunch of ten stems; ‘speculation’ grade stems were 20–25 cm in length, free of curvature or visual deformities, and sold for $12.50 per bunch of ten stems; and ‘cull’ grade stems were less than 20 cm in length, curved or deformed, and not marketable. An economic budget was calculated for ranunculus based on cost, yield, and sales by management practice (planting × insulation × pre-sprouting) on a 52 m2 high tunnel or field production area containing 994 plants. All input costs for production and transport were recorded [11] and stems were sold wholesale from Apr. to Jul. through a local cut flower co-op that marketed to florists in Logan, Salt Lake City, and Park City, Utah. Crop value was calculated by scaling the average yield of quality-grade stems for each combination of management practices to a whole high tunnel or field and multiplying by the price ($1.50 per stem) and the percent expected to sell to florists (assumed to be 100%). Net returns were then calculated as the difference between crop value and input costs.
Yield (stems per m2) was calculated by dividing the number of stems harvested by the number of TRs planted in one replication and multiplying by a plant density of 44 plants per m2, without accounting for how many plants emerged. First harvest was considered the date of harvest of the first flower, regardless of its quality grade (i.e., total yield). The time to reach 20% (T20), 50% (T50), and 80% (T80) of marketable yield were calculated, with T50 representing the harvest midpoint and the time from T20 to T80 (T20–80) representing the duration of peak harvest. Descriptive statistics are presented for 2019–20 data, and an ANOVA-type mixed model was used to compare emergence, production timing, total yield, and marketable yield among insulation, planting date, pre-sprouting, and cultivar treatments within the high tunnel and field in 2020–21 and 2021–22. Percentages of emergence were transformed using logit, while total yield, marketable yield, and T20–80 were log transformed. The proportions of each of the three stem quality grades were compared across treatments with a mixed model on categorical outcomes. All statistical analyses were performed with PROC GLIMMIX of SAS Studio (SAS Institute, Cary, NC, USA) using a significance level of α = 0.05.
Grower collaborators collected additional winter survival and yield data along Utah’s Wasatch Front from 2019–22. Participants consisted of six growers in 2019–20, eleven growers in 2020–21, and seven growers in 2021–22, from across Cache, Weber, Davis, Salt Lake, and Utah counties (USDA hardiness zones 5 to 7). Participants, ranging from skilled hobbyists to micro farmers with no to moderate experience growing ranunculus, were provided ten ranunculus ‘LaBelle’ TRs to plant each fall and spring. Growers planted at a 0.05 m depth and recorded management decisions regarding planting dates, winter insulation, pre-sprouting, fertilization, and irrigation.

3. Results

3.1. Environmental Conditions (15 Nov.–15 Jul.)

Total precipitation (rainfall and a snow water equivalent) over the growing season was 301 mm in 2019–20, 153 mm in 2020–21, and 178 mm in 2021–22, which were all less than the 30-year normal (1981–2010) of 359 mm [44]. Total snowfall was 1581 mm in 2019–20, 762 mm in 2020–21, and 516 mm in 2021–22, and total solar radiation ranged from 3714 MJ·m−2 to 4195 MJ·m−2 over the growing season each year. Monthly average air temperatures were near the 30-year normal across the study period in all years [44]. From Nov. 15 to Mar. 1 each year, the average air temperature (2 m height) ranged from −2.2 to −2.9 °C (Figure 1), and from 1 Mar. to 15 Jul., the average air temperature ranged from 11.5 °C to 13.3 °C. The daily average air temperature first reached 25 °C on 30 May 2020, 5 Jun. 2021, and 17 Jun. 2022.
Bare soil (-LT-M) at a 0.05 m depth froze from 18 Dec. 2019 to 3 Mar. 2020, 25 Nov. 2020 to 4 Mar. 2021, and 18 Nov. 2021 to 12 Mar. 2022 (Figure 2). The minimum bare soil temperature was −3.0 °C (21 Feb.) in 2020, −7.2 °C (13 Dec.) in 2021, and −6.4 °C (24 Feb.) in 2022, while the total time bare soil temperature was at or below −3.0 °C was 3 hrs in 2019–20, 76 hrs in 2020–21, and 339 hrs in 2021–22. Compared to bare soil each year, the average hourly soil temperature was 1.5 to 2.1 °C greater for -LT+M, 1.7 to 3.5 °C greater for +LT-M, and 1.9 to 2.2 °C greater for +LT+M. In the high tunnel, air temperature was 2.0 ± 0.0 °C greater in +LT than -LT in both 2020–21 and 2021–22 (Figure 1). Soil temperature was 0.2 ± 0.0 °C greater in +LT than -LT in 2019–20, 1.2 ± 0.0 °C greater in 2020–21, and 0.6 ± 0.0 °C greater in 2021–22. Soil temperature was below 0 °C for a total of 8 hrs for +LT and 8 hrs for -LT in 2019–20, 7 hrs for +LT and 51 hrs for -LT in 2020–21, and 18 hrs for +LT and 78 hrs for -LT in 2021–22.

3.2. Emergence

In 2019–20, field emergence was 89 ± 11% for Nov. and 100 ± 0% for Mar. and Apr. plantings. For the Nov. field planting in 2019–20, 67 ± 7% of -LT-M TRs emerged, while 97 ± 3% of +LT+M TRs emerged. Across 2020–21 and 2021–22, emergence for the Nov. planting was 44 ± 2% for -LT-M TRs compared to 95 ± 2% for TRs with any form of insulation (+LT-M, -LT+M, or +LT+M; p < 0.0001). For -LT-M TRs planted in Nov., emergence was 72 ± 3% for -PS compared to 42 ± 2% for +PS (p = 0.0057). Emergence of -LT-M TRs planted in Nov. was 58 ± 7% for 2020–21 compared to 33 ± 8% for 2021–22 (p < 0.0001). For Mar. and Apr. plantings, emergence was 98 ± 1% with no significant differences observed by year, insulation, pre-sprouting, or cultivar. In 2019–20, 94 ± 2% of TRs planted in the high tunnel emerged regardless of planting date or insulation. High tunnel emergence across 2020–21 and 2021–22 and all management practices tested was 97 ± 0%. No significant differences in high tunnel emergence were observed by year or management practice.

3.3. Harvest Timing

In the field, harvest began between 5 and 13 May for Nov. plantings, 1 and 4 Jun. for Mar. plantings, and 8 and 14 Jun. for Apr. plantings each year (Figure 3). Harvest ended between 2 and 7 Jul. for Nov. plantings and 6 and 11 Jul. for Mar. and Apr. plantings. First harvest and T50 occurred 5 days sooner in 2021 than 2022 on average (p = 0.0018 and p = 0.0008, respectively). First harvest of Nov. plantings occurred 17 ± 1 days sooner with insulation compared to -LT-M (p < 0.0001). First harvest occurred 3 ± 0 days sooner for +PS than -PS (p < 0.0001) and 1 ± 0 days sooner for ‘Amandine’ than ‘LaBelle’ (p = 0.0162). T50 occurred on 31 May for Nov. plantings, 14 Jun. for Mar. plantings, and 25 Jun. for Apr. plantings, on average across 2021 and 2022. T50 occurred 5 ± 1 days sooner for +LT+M than -LT-M (p < 0.0001) and 3 ± 0 days sooner for +PS than -PS (p < 0.0001). T20-T80 lasted 9 ± 0 days for Nov. plantings, 7 ± 0 days for Mar. plantings, and 6 ± 0 days for Apr. plantings.
On average across all three years, high tunnel harvest began 30 ± 3 days sooner than field harvest, beginning on 8, 6, and 11 Apr., and ending on 10 Jul., 30 Jun., and 23 Jun. in 2019–20, 2020–21, and 2021–22, respectively (Figure 4). First harvest occurred on 8, 6, and 11 Apr. for Nov. plantings, 22 Apr. and 2 May for Jan. plantings (no Jan. planting occurred in 2019–20), 15 Apr., 5 May, and 2 May for Feb. plantings, and 15, 20, and 12 May for Mar. plantings in 2019–20, 2020–21, and 2021–22, respectively. First harvest occurred 4 ± 1 days sooner for +PS than -PS (p = 0.0191). T50 occurred on 5 May for Nov. plantings, 16 May for Jan. plantings, 26 May for Feb. plantings, and 8 Jun. for Mar. plantings, on average across 2021 and 2022. T20-T80 lasted 20 ± 0 days for Nov. plantings, 13 ± 1 days for Jan. plantings, 11 ± 1 days for Feb. plantings, and 7 ± 0 days for Mar. plantings. T20-T80 lasted 2 ± 0 days longer for +PS than -PS (p = 0.0422).

3.4. Field Yield

The total field yield in 2020 ranged from 29 to 158 stems per m2, with an average yield of 88 ± 8 stems per m2 and 94 ± 2% marketability. Marketable yield ranged from 29 to 151 stems per m2, with an average of 83 ± 8 stems per m2 (Figure 3). Marketable yield was 78 ± 14 stems per m2 for ‘Amandine’ and 105 ± 17 stems per m2 for ‘LaBelle.’ Marketable yield was 70 ± 12 stems per m2 for the Nov. planting, 95 ± 17 stems per m2 for the Mar. planting, and 80 ± 12 stems per m2 for the Apr. planting. For the Nov. ‘LaBelle’ planting, marketable yield was 39 stems per m2 for –LT-M and 100 stems per m2 for +LT+M.
Across 2021 and 2022, average total field yields ranged from 15 to 129 stems per m2, with an overall average yield of 78 ± 2 stems per m2 (Table 1). Average marketable yields ranged from 15 to 105 stems per m2, with an overall average of 61 ± 2 stems per m2 (Table 1 and Figure 3) and no significant differences by year. For Nov. planted TRs, marketable yield was 49 ± 8 stems per m2 greater with any type of insulation compared to bare soil (p < 0.0001). No significant differences in marketable yield by insulation were observed for Mar. or Apr. plantings. Marketable yield was 50 ± 4 stems per m2 for the Nov. planting, 67 ± 5 stems per m2 for the Mar. planting, and 40 ± 3 stems per m2 for the Apr. planting. Marketable yield was 23 ± 4 stems per m2 greater for the Mar. planting than the Nov. or Apr. plantings (p < 0.0001) and 6 ± 3 stems per m2 greater for ‘LaBelle’ than ‘Amandine’ (p = 0.0232). Marketable yield was 21 ± 5 stems per m2 greater for +PS than -PS for Mar. and Apr. plantings (p < 0.0001), and 20 ± 5 stems per m2 less for +PS than -PS for Nov. plantings (p < 0.0001).
The average marketability (including quality and speculation grades) of field stems across 2021 and 2022 was 77 ± 1%. Of the total yield across all treatments, 48 ± 1% of stems were quality grade, 28 ± 1% were speculation grade, and 23 ± 1% were cull grade. In 2022, 29 ± 3% of stems were cull grade, compared to 17 ± 3% in 2021 (p = 0.0443). 51 ± 2% of ‘Amandine’ stems were quality grade compared to 45 ± 2% of ‘LaBelle’ stems (p = 0.0147). Mar. plantings produced the most quality grade stems (55 stems per m2) compared to Nov. (36 stems per m2) or Apr. plantings (28 stems per m2; p < 0.0001; Figure 5).

3.5. High Tunnel Yield

Total high tunnel yield in 2020 ranged from 33 to 201 stems per m2, with an average yield of 115 ± 7 stems per m2 and 93 ± 1% marketability. Marketable yield ranged from 38 to 158 stems per m2, with an average of 106 ± 6 stems per m2 (Figure 4). Marketable yield was 92 ± 10 stems per m2 for ‘Amandine’ compared to 119 ± 7 stems per m2 for ‘LaBelle.’ Marketable yield was 123 ± 8 stems per m2 for Nov. plantings, 103 ± 8 stems per m2 for Feb. plantings, and 92 ± 13 stems per m2 for Mar. plantings. Marketable yield by insulation was 118 ± 9 for -LT and 94 ± 8 for +LT.
Across 2021 and 2022, average total high tunnel yields ranged from 43 to 316 stems per m2, with an overall average yield of 178 ± 7 stems per m2 (Table 2). Average marketable yields ranged from 32 to 286 stems per m2, with an overall average of 163 ± 7 stems per m2. No significant differences in marketable yield by year or insulation were observed. Marketable yield decreased with each subsequent planting date (p < 0.0001), from 250 ± 21 stems per m2 for Nov. plantings to 171 ± 14 stems per m2 for Jan. plantings, 133 ± 11 stems per m2 for Feb. plantings, and 53 ± 4 stems per m2 for Mar. plantings. Marketable yield was 44 ± 9 stems per m2 greater for +PS than -PS (p = 0.0005) and 34 ± 8 stems per m2 greater for ‘LaBelle’ than ‘Amandine’ (p < 0.0001).
The average marketability of high tunnel stems across 2021 and 2022 was 87 ± 1% and did not vary significantly by year. Of the total yield across all treatments, 72 ± 1% of stems were quality grade, 15 ± 1% were speculation grade, and 13 ± 1% were cull grade. ‘Amandine’ produced 24 ± 1% more cull grade stems (p = 0.0408) and 21 ± 1% more speculation grade stems than ‘LaBelle.’ Of the total stems, quality grade stems made up 79 ± 3% for +LT compared to 65 ± 3% for -LT (p = 0.0117), and 76 ± 2% for +PS compared to 68 ± 2% for -PS (p = 0.0301). The yield of quality grade stems decreased with each planting date, from 246 stems per m2 for Nov. to 48 stems per m2 for Mar. plantings (p < 0.05; Figure 5).

3.6. Marketing and Crop Value

Of the marketable stems harvested in 2021 and 2022 (including quality and speculation grades), 56% were purchased by florists, 10% were unsold, and 34% were not marketed due to losses in storage and handling. The estimated crop value (quality-grade stems only) across management practices ranged from $29 per m2 to $172 per m2 in the high tunnel and $6 per m2 to $28 per m2 in the field. High tunnel production costs consisted of a co-op delivery fee (45%), labor (36%), supplies (14%), and high tunnel construction (5%), compared to field production costs of labor (44%), a co-op delivery fee (28%), supplies (27%), and land (1%). Based on these costs, in the high tunnel, Nov. and Jan. plantings always produced positive returns, while Feb. plantings only produced positive returns when pre-sprouting was used, and Mar. plantings always produced negative returns. The highest net returns of $54 per m2 were calculated for a Nov. high tunnel planting with pre-sprouting and no low tunnels. Calculated field economic returns were always negative, with losses ranging from $9 to $33 per m2 across management practices.

3.7. On-Farm Trials

Of the 18 full sets of yield data submitted across the study, the average yield (in stems per plant) was 4.4 ± 1.0 total and 3.4 ± 0.8 marketable for fall-planted TRs and 3.3 ± 0.7 total and 2.5 ± 0.6 marketable for spring-planted. Total yields ranged from 0 to 13.7 stems per plant and marketable yields ranged from 0 to 10.9 stems per plant. Management practices varied by grower, with 29% of growers choosing to pre-sprout TRs. One grower used a high tunnel, while for fall plantings 20% of growers left TRs bare, 20% insulated with mulch alone, 33% insulated with a low tunnel alone, and 20% insulated with mulch and a low tunnel. Four growers noted poor (<40%) emergence of TRs planted in the fall and left bare, while one grower’s fall-planted TRs emerged but never flowered. The high tunnel grower (USDA hardiness zone 5b) did not pre-sprout and had marketable yields in the range of 7.1 to 10.9 stems per plant, while most of the field growers had marketable yields ranging from 0.8 to 4.7 stems per plant with no apparent patterns by growing experience or hardiness zone. Field growers who planted TRs in the fall with no insulation had the lowest yields, with the exception of one grower (USDA hardiness zone 6b) who did not soak their TRs before planting in the fall, left the soil bare, and obtained the highest marketable yield (10.0 stems per plant) of any field grower.

4. Discussion

In the high tunnel, harvest began more than five weeks before the average last frost date and four weeks earlier than the field. By allowing for vegetative growth throughout the winter and marketable flowers beginning in early April, high tunnels maximized time at growing conditions in the optimal temperature range of 5 to 20 °C, resulting in annual yields that were nearly double field yields and on par with traditional production regions. For example, the greatest average total yield of 316 stems per m2 (7.2 stems per plant) was comparable to total yields of 9.4 to 11.5 stems per plant obtained in a soilless cultivation high tunnel system in Israel [8]. In contrast, the maximum total field yield of 129 stems per m2 (2.9 stems per plant) was likely limited by below-freezing temperatures in spring and high temperatures during peak production. High tunnel production increased the proportion of quality stems (>25 cm length) by 50% compared to the field, likely because of reduced air movement and shading in the high tunnel. Studies of other cut flower crops also reported longer cut flower stem lengths, and hence improved quality, from high tunnels compared to field production systems [14,28,29,30].
Earlier plantings in the high tunnel and field had more time to flower before temperatures became superoptimal, which advanced first harvest and T50 dates, increased yields, and extended T20-T80 periods compared to later plantings. Flowering before the average daily air temperatures were consistently above 25 °C (i.e., between late June and mid-July) optimized production, after which flowering ceased and plants began to senesce. Fall planting in the field has not been recommended for USDA hardiness zone 5 due to risk of cold injury [2], which was supported by uninsulated November plantings that exhibited emergence between 33 (pre-sprouted) and 67% (nonpre-sprouted) and marketable yields between 15 and 39 stems per m2. Moreover, four growers in on-farm trials reported emergence of 40% or less for uninsulated fall field plantings, indicating that cold injury is a risk of fall planting up to USDA hardiness zone 7. However, fall planting with low-cost insulation methods, such as low tunnels and straw mulch, optimized emergence and yield for the field production system. For example, the average onset of flowering for November field plantings was 9 May and lasted eight weeks, whereas April plantings began on 11 Jun., when temperatures were already superoptimal, and only flowered for four weeks before senescing. With twice as much time to flower under optimal temperatures, the average marketable yield of November plantings (69 stems per m2 with any winter insulation, and thus, protection from cold injury) was 73% greater than that of April plantings (40 stems per m2).
Year-to-year variability in weather highlights the importance of using insulation to mitigate the risks of fall-planted field production. The emergence of uninsulated fall plantings was reduced by 76% and harvest timing was delayed by approximately one week in 2021–22 compared to 2020–21, likely because bare soil was frozen for nearly 500 more hours in 2021–22 than 2020–21 as a result of colder air temperatures and less consistent snow cover. Though all insulation types improved the yield of fall plantings, soil temperature fluctuated the most and reached a minimum of −4.6 °C with low tunnels alone, indicating that mulch buffered soil heat losses and may reduce year-to-year risk from variability in weather [18]. Insulation was unnecessary for spring field plantings, which showed no differences in emergence or yield since insulation treatments were removed from the field before or shortly after April plantings. Although ‘Amandine’ was marketed as relatively heat-tolerant and ‘LaBelle’ was marketed as relatively cold-tolerant [34], we found little evidence to support this claim. ‘LaBelle’ outperformed ‘Amandine’ in both total and marketable yield in the field and high tunnel, both for early planting dates when cold was limiting and for later planting dates when heat would be more likely to limit production.
A two-week pre-sprouting period, popular among small growers [1,13], resulted in visible roots and small shoots at the time of planting, as well as additional vegetative growth that improved yield for high tunnel and spring field plantings. Pre-sprouting advanced harvest up to one week compared to nonpre-sprouted plantings, with the earliest flower obtained on 6 Apr. Similarly, a three-week pre-sprouting period advanced ranunculus flowering by three days in a NY high tunnel trial (USDA hardiness zone 5) with the first flower occurring on 2 May [10]. Season advancement earlier than April may be limited by the time of year, as average daily air temperatures were typically below 10 °C in the high tunnel and daylengths were below 13 h until the end of March. In a greenhouse study, ranunculus flowered the fastest under long (20 hrs) days and a night temperature of 15 °C, suggesting a minimum temperature and/or photoperiod for flowering that was not reached until April in our study and warrants further investigation [35]. In the field, pre-sprouting decreased emergence by 42% and marketable yield by 33% for uninsulated November plantings, as the early root and shoot growth of pre-sprouted TRs may have increased susceptibility to cold injury compared to their dormant counterparts [20]. While pre-sprouting fall field plantings risks cold injury, pre-sprouting benefits high tunnel and spring field production by accelerating vegetative growth and increasing yield.
The calculated costs of production were similar across management practices in the high tunnel and field, making net economic returns largely dependent on quality-grade yield [11]. Florists were more likely to purchase quality-grade stems than speculation-grade stems, with the most speculation-grade stems selling within the first month of the season (i.e., April) when other local flowers were less available. Ranunculus has the potential to be a premium high value crop for small farms with high tunnels, as November planting with presprouting maximized quality grade yield and resulted in net returns up to $54 per m2. The profit potential of ranunculus was more than double that of other high tunnel cut flowers, such as peony and snapdragon, that yielded net returns of $18 and $28 per m2, respectively [45,46]. Net returns were approximately double those of snapdragon due to the high planting density of ranunculus, which more than tripled its marketable yield per unit area compared to snapdragon. Moreover, the early season timing of fall-planted ranunculus may also allow growers to produce a second crop in the same high tunnel [28]. For example, planting a warm season crop in June, such as dahlia, would maximize the use of limited space and generate additional returns, further increasing small farm profitability. While field ranunculus production improved using early spring or insulated fall plantings, average yields were 20 stems short of the 70 quality stems per m2 minimum yield needed to generate positive returns with local wholesale market channels. However, many Utah cut flower growers sell direct to consumers through farmer’s markets, CSAs, social media, and on-farm events, creating a market for shorter stems with higher markups. While ranunculus production from high tunnels is highly profitable, field production also has potential when retail marketing channels are used.

5. Conclusions

Planting pre-sprouted ranunculus tuberous roots in November delivered the earliest harvests and greatest yields, stem quality, and net returns in a USDA hardiness zone 5 high tunnel production system. Succession planting of ‘LaBelle’ in high tunnels from November through January may allow growers to produce a consistent supply of flowers for wholesale markets from the beginning of April to the end of May before planting a warm season crop in June. High tunnel plantings after mid-February are not recommended as harvests beginning in mid-May or later are limited by superoptimal air temperatures by late June. For growers lacking the space for a high tunnel, combining nonpre-sprouted, insulated November plantings and pre-sprouted March plantings supplies smaller yields of ranunculus for diversified marketing channels from the beginning of May to the end of June.

Author Contributions

Conceptualization, S.R. and M.S.; Data curation, S.R.; Formal analysis, S.R., M.S., X.D. and R.W.; Funding acquisition, M.S., B.B. and D.D.; Investigation, S.R. and M.S.; Methodology, S.R., M.S. and X.D.; Project administration, M.S.; Resources, M.S., B.B. and D.D.; Supervision, M.S.; Visualization, S.R., M.S. and X.D.; Writing—original draft, S.R.; Writing—review and editing, M.S., B.B., D.D., X.D. and R.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by a USDA-NIFA Specialty Crop Block Grant administered by the Utah Department of Agriculture, the Association of Specialty Cut Flower Growers, a United States Department of Agriculture (USDA) National Needs Fellowship, the Utah State University Plants, Soils & Climate department, and the Utah Agricultural Experiment Station, Utah State University, journal paper number UAES #9627.

Data Availability Statement

Data is contained within the article.

Acknowledgments

We would like to thank James Frisby of Utah State University and our undergraduate students, Kasey Battson, Anna Collins, and Olive Stewart, for their technical assistance, as well as Katelyn Fritz for her friendly review of this paper.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Figure 1. Average daily air temperature in 2019−20 (top), 2020−21 (middle), and 2021−22 (bottom) in an uninsulated field (light green line), a field covered with low tunnels (dark green line), a high tunnel (light blue line), and a low tunnel within a high tunnel (dark blue line) in North Logan, UT. Air temperature was measured at a 2.0 m height in 2019−20 [23] and 0.25 m height in 2020−21 and 2021−22. Vertical gray lines marked with F, H, and P denote the dates field low tunnels, high tunnel low tunnels, and high tunnel plastic were removed, respectively.
Figure 1. Average daily air temperature in 2019−20 (top), 2020−21 (middle), and 2021−22 (bottom) in an uninsulated field (light green line), a field covered with low tunnels (dark green line), a high tunnel (light blue line), and a low tunnel within a high tunnel (dark blue line) in North Logan, UT. Air temperature was measured at a 2.0 m height in 2019−20 [23] and 0.25 m height in 2020−21 and 2021−22. Vertical gray lines marked with F, H, and P denote the dates field low tunnels, high tunnel low tunnels, and high tunnel plastic were removed, respectively.
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Figure 2. Average daily snowfall (light blue bars) [42] and soil temperature (0.05 m depth) during the winter of 2019−20 (top), 2020−21 (middle), and 2021−22 (bottom) under no cover (-LT-M; blue line), mulch (-LT+M; green line), a fabric low tunnel (+LT-M; yellow line), and mulch and a fabric low tunnel (+LT+M; red line) in the field in North Logan, UT.
Figure 2. Average daily snowfall (light blue bars) [42] and soil temperature (0.05 m depth) during the winter of 2019−20 (top), 2020−21 (middle), and 2021−22 (bottom) under no cover (-LT-M; blue line), mulch (-LT+M; green line), a fabric low tunnel (+LT-M; yellow line), and mulch and a fabric low tunnel (+LT+M; red line) in the field in North Logan, UT.
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Figure 3. Cumulative marketable field yield of ‘Amandine’ (left) and ‘LaBelle’ (right) ranunculus in 2019–20 (top), 2020–21 (middle), and 2021–22 (bottom) in North Logan, UT by planting date (Nov.–blue; Mar.—red; Apr.—green) that were uncovered (-LT-M—solid) or insulated with mulch (-LT+M—long dashes), a low tunnel (+LT-M—short dashes), or mulch and a low tunnel (+LT+M—dots). T20 (diamonds), T50 (circles), and T80 (triangles) mark the completion of 20, 50, and 80% of marketable yield, respectively.
Figure 3. Cumulative marketable field yield of ‘Amandine’ (left) and ‘LaBelle’ (right) ranunculus in 2019–20 (top), 2020–21 (middle), and 2021–22 (bottom) in North Logan, UT by planting date (Nov.–blue; Mar.—red; Apr.—green) that were uncovered (-LT-M—solid) or insulated with mulch (-LT+M—long dashes), a low tunnel (+LT-M—short dashes), or mulch and a low tunnel (+LT+M—dots). T20 (diamonds), T50 (circles), and T80 (triangles) mark the completion of 20, 50, and 80% of marketable yield, respectively.
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Figure 4. Cumulative marketable high tunnel yield of ‘Amandine’ (left) and ‘LaBelle’ (right) ranunculus in 2019–20 (top), 2020–21 (middle), and 2021–22 (bottom) in North Logan, UT by planting date (Nov.—blue; Jan.—aqua; Feb.—yellow; Mar.—red) that were pre-sprouted (+PS; dashed) or not pre-sprouted (-PS; solid). T20 (diamonds), T50 (circles), and T80 (triangles) mark the completion of 20, 50, and 80% of marketable yield, respectively.
Figure 4. Cumulative marketable high tunnel yield of ‘Amandine’ (left) and ‘LaBelle’ (right) ranunculus in 2019–20 (top), 2020–21 (middle), and 2021–22 (bottom) in North Logan, UT by planting date (Nov.—blue; Jan.—aqua; Feb.—yellow; Mar.—red) that were pre-sprouted (+PS; dashed) or not pre-sprouted (-PS; solid). T20 (diamonds), T50 (circles), and T80 (triangles) mark the completion of 20, 50, and 80% of marketable yield, respectively.
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Figure 5. The average ranunculus yield in stems per m2 by planting date and insulation in a North Logan, UT field (top) and high tunnel (bottom) across 2020–21 and 2021–22. In the field, plants were covered with no insulation (-LT-M), mulch (-LT+M), a low tunnel (+LT-M), or a low tunnel and mulch (+LT+M). In the high tunnel, plants were covered with no insulation (-LT) or a low tunnel (+LT). Stems were graded as quality (greater than 25 cm stem length), speculation (20–25 cm), or cull (<20 cm). Mean total yields marked by bolded different letters at the top of a bar and means marked by different letters within a length category are significantly different according to Tukey’s HSD test at α = 0.05.
Figure 5. The average ranunculus yield in stems per m2 by planting date and insulation in a North Logan, UT field (top) and high tunnel (bottom) across 2020–21 and 2021–22. In the field, plants were covered with no insulation (-LT-M), mulch (-LT+M), a low tunnel (+LT-M), or a low tunnel and mulch (+LT+M). In the high tunnel, plants were covered with no insulation (-LT) or a low tunnel (+LT). Stems were graded as quality (greater than 25 cm stem length), speculation (20–25 cm), or cull (<20 cm). Mean total yields marked by bolded different letters at the top of a bar and means marked by different letters within a length category are significantly different according to Tukey’s HSD test at α = 0.05.
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Table
Table 1. Field ranunculus production by calculated mean(±SE) total and marketable yields in stems per m2 by cultivar (‘Amandine’ and ‘LaBelle’), pre-sprouting (pre-sprouted +PS and nonpre-sprouted -PS), insulation (no insulation -LT-M, mulch -LT+M, low tunnel +LT-M, and low tunnel and mulch +LT+M), and planting date (Nov., Mar., and Apr.) in North Logan, UT over 2020–21 and 2021–22.
Table 1. Field ranunculus production by calculated mean(±SE) total and marketable yields in stems per m2 by cultivar (‘Amandine’ and ‘LaBelle’), pre-sprouting (pre-sprouted +PS and nonpre-sprouted -PS), insulation (no insulation -LT-M, mulch -LT+M, low tunnel +LT-M, and low tunnel and mulch +LT+M), and planting date (Nov., Mar., and Apr.) in North Logan, UT over 2020–21 and 2021–22.
Total Yield (Stems per m2) Marketable Yield (Stems per m2)
Planting Date
CultivarPSInsulationNov.Mar.Apr. Nov.Mar.Apr.
‘Amandine’+PS-LT-M15 ± 3 B, b, Y84 ± 16 A, a, X69 ± 13 A, a, X 15 ± 4 B, b, Y71 ± 15 A, a, X53 ± 12 A, a, X
-LT+M60 ± 12 A, a, X88 ± 19 A, a, X62 ± 12 A, a, X 46 ± 10 A, a, X71 ± 17 A, a, X45 ± 10 A, a, X
+LT-M66 ± 13 A, a, Y97 ± 19 A, a, X74 ± 14 A, a, X 56 ± 12 A, a, X84 ± 18 A, a, X53 ± 11 A, a, X
+LT+M79 ± 15 A, a, X88 ± 17 A, a, X55 ± 11 A, a, X 64 ± 14 A, a, X75 ± 16 A, a, X39 ± 9 A, a, X
-PS-LT-M30 ± 7 B, b, X66 ± 13 A, a, X27 ± 5 B, a, Y 29 ± 8 A, b, X57 ± 12 A, a, X28 ± 7 A, a, Y
-LT+M90 ± 17 A, a, X73 ± 14 A, a, X38 ± 7 B, a, Y 61 ± 13 A, ab, X51 ± 11 AB, a, X28 ± 6 B, a, X
+LT-M111 ± 21 A, a, X70 ± 13 A, a, X29 ± 6 B, a, Y 91 ± 20 A, a, X59 ± 13 A, a, X22 ± 5 B, a, Y
+LT+M114 ± 22 A, a, X60 ± 12 B, a, X32 ± 6 B, a, Y 95 ± 21 A, a, X44 ± 10 B, a, Y28 ± 7 B, a, X
‘LaBelle’+PS-LT-M23 ± 5 B, b, X103 ± 20 A, a, X74 ± 14 A, a, X 18 ± 5 B, b, X85 ± 18 A, a, X45 ± 10 A, a, X
-LT+M81 ± 16 A, a, X99 ± 19 A, a, X91 ± 18 A, a, X 29 ± 6 B, b, Y74 ± 16 A, a, X70 ± 15 A, a, X
+LT-M71 ± 14 A, a, X129 ± 25 A, a, X76 ± 15 A, a, X 67 ± 16 A, a, X101 ± 22 A, a, X58 ± 13 A, a, X
+LT+M110 ± 21 A, a, X110 ± 21 A, a, X73 ± 14 A, a, X 88 ± 19 A, a, X80 ± 17 AB, a, X42 ± 9 B, a, X
-PS-LT-M25 ± 5 B, b, X78 ± 15 A, a, X42 ± 8 AB, a, Y 20 ± 5 B, b, X68 ± 15 A, a, X22 ± 5 B, b, Y
-LT+M117 ± 23 A, a, X65 ± 12 A, a, X73 ± 14 A, a, X 77 ± 17 A, a, X44 ± 10 A, a, Y55 ± 12 A, a, X
+LT-M108 ± 21 A, a, X81 ± 16 AB, a, X46 ± 9 B, a, Y 73 ± 16 A, a, X72 ± 16 A, a, X38 ± 8 A, ab, X
+LT+M127 ± 24 A, a, X80 ± 15 AB, a, X66 ± 13 B, a, X 105 ± 23 A, a, X66 ± 14 AB, a, X46 ± 10 B, ab, X
A, B: Planting date difference. For each type of yield, least squares means with the same letter within a row indicates no statistical difference at α = 0.05. a, b: Insulation difference. For each type of yield, least squares means with the same letter within a column under the same pre-sprouting indicates no statistical difference at α = 0.05. X, Y: Pre-sprouting difference. For each type of yield, least squares means with the same letter within a column under the same insulation indicates no statistical difference at α = 0.05.
Table
Table 2. High tunnel ranunculus production by calculated mean(±SE) total and marketable yields in stems per m2 by cultivars (‘Amandine’ (AM) and ‘LaBelle’ (LB)), pre-sprouting (pre-sprouted +PS and nonpre-sprouted -PS), and planting dates (Nov., Jan., Feb., and Mar.) in North Logan, UT over 2020–21 and 2021–22.
Table 2. High tunnel ranunculus production by calculated mean(±SE) total and marketable yields in stems per m2 by cultivars (‘Amandine’ (AM) and ‘LaBelle’ (LB)), pre-sprouting (pre-sprouted +PS and nonpre-sprouted -PS), and planting dates (Nov., Jan., Feb., and Mar.) in North Logan, UT over 2020–21 and 2021–22.
Total Yield (Stems per m2)Marketable Yield (Stems per m2)
Planting Date
CultivarPSNov.Jan.Feb.Mar.Nov.Jan.Feb.Mar.
AM+PS281 ± 34 A, a, X192 ± 23 AB, a, X153 ± 19 B, a, X71 ± 9 C, a, Y261 ± 33 A, a, X180 ± 23 AB, a, X138 ± 17 B, a, Y57 ± 7 C, a, Y
-PS214 ± 26 A, a, Y166 ± 20 AB, a, X117 ± 14 B, a, Y43 ± 5 C, b, X202 ± 26 A, a, X152 ± 19 A, a, X90 ± 11 B, b, Y32 ± 4 C, b, Y
LB+PS316 ± 38 A, a, X196 ± 24 B, a, X201 ± 25 B, a, X102 ± 12 C, a, X286 ± 36 A, a, X187 ± 24 A, a, X188 ± 24 A, a, X94 ± 12 B, a, X
-PS286 ± 35 A, a, X182 ± 22 B, a, X159 ± 19 B, a, X46 ± 6 C, b, X259 ± 33 A, a, X168 ± 21 B, a, X136 ± 17 B, a, X46 ± 6 C, b, X
A, B, C: Planting date difference. For each type of yield, least squares means with the same letter within a row indicates no statistical difference at α = 0.05. a, b: Pre-sprouting difference. For each type of yield, least squares means with the same letter within a column under the same cultivar indicates no statistical difference at α = 0.05. X, Y: Cultivar difference. For each type of yield, least squares means within a column under the same pre-sprouting indicates no statistical difference at α = 0.05.
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Rauter, S.; Stock, M.; Black, B.; Drost, D.; Dai, X.; Ward, R. Overwintering Improves Ranunculus Cut Flower Production in the US Intermountain West. Horticulturae 2022, 8, 1128. https://doi.org/10.3390/horticulturae8121128

AMA Style

Rauter S, Stock M, Black B, Drost D, Dai X, Ward R. Overwintering Improves Ranunculus Cut Flower Production in the US Intermountain West. Horticulturae. 2022; 8(12):1128. https://doi.org/10.3390/horticulturae8121128

Chicago/Turabian Style

Rauter, Shannon, Melanie Stock, Brent Black, Dan Drost, Xin Dai, and Ruby Ward. 2022. "Overwintering Improves Ranunculus Cut Flower Production in the US Intermountain West" Horticulturae 8, no. 12: 1128. https://doi.org/10.3390/horticulturae8121128

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