Abstract
Over the past two decades, interest in local specialty cut flower production in eastern South Dakota has grown, with several new flower farms being established across the region. However, there is currently no local, research-based information available to support growers in this new wave of interest. The purpose of this study was to assess the production and quality of four zinnia cultivars grown in eastern South Dakota to support local specialty cut flower growers in their operations. A randomized complete block design was used to evaluate four zinnia cultivars (Zinderella Peach, Oklahoma Ivory, Queen Red Lime, and Benary’s Giant Purple) grown in 2022 and 2023. Zinnias were started by seed in the greenhouse and transplanted into the field in early summer each season. Harvest began each year when flowers reached maturity (July), with one harvest event taking place each week until the first frost. Harvested flowers were rated as marketable or nonmarketable based on categories of stem length (≥18-inch-long, 13- to 17.99-inch-long, 8- to 12.99-inch-long, and <8-inch-long stems), as well as nonmarketable due to defects (curved stems, insect damage, and other damage). ‘Benary’s Giant Purple’ produced high numbers of marketable long stems and had the largest bloom size, whereas ‘Queen Red Lime’ and ‘Oklahoma Ivory’ produced high numbers of marketable medium-length stems and had lower amounts of insect damage. ‘Zinderella Peach’ produced the shortest and most insect-damaged stems and also produced lower numbers of curved stems compared with the other three cultivars. All four cultivars produced high numbers of marketable flowers and would be suitable choices for specialty cut flower growers in eastern South Dakota.
Interest in local specialty cut flower production in the United States has been increasing for the past two decades (Langford et al. 2023; Loyola et al. 2019). In eastern South Dakota, multiple new flower farms have been established in the past 5 years (Association of Specialty Cut Flower Growers 2024). Furthermore, studies have shown an increase in consumer interest in locally and sustainably produced cut flowers in the Midwest (Etheredge et al. 2024). However, there is currently no local, research-based information to support the new wave of interest among South Dakota cut flower farmers. This lack of information makes growing specialty cut flowers especially challenging for local growers. Specialty cut flowers have different production and postharvest needs compared with traditional cut flowers such as roses, carnations, and mums (Nobes et al. 2022). Local growers can provide specialized varieties that do not ship well and therefore fill a niche left open by larger international companies (Langford et al. 2023). Zinnias, peonies, snapdragons, and sunflowers are among specialized varieties that have intrigued local producers in the past few years (Loyola et al. 2019).
Zinnias were chosen for this study because they are a warm-season crop that can withstand hot summers (Ahmad et al. 2017), which are typical in eastern South Dakota. Zinnia hardiness, along with their bright, appealing color and shape, make them a popular choice to grow for specialty cut flower farmers around the world (Ahmad et al. 2017). Their popularity continues to grow in the United States (Langford et al. 2023). There are 20 species of zinnias, but Zinnia elegans is the most popular (Klingaman 2007). Zinnias have a large head with brightly colored petals and come in every color of the rainbow except for blue (Coker and DelPrince 2022). Some are even bicolored, as seen in the cultivar Queen Red Lime (QRL) (Fig. 1). Many cultivars and varieties exist within the Z. elegans species, and several of these cultivars produce flower heads with varying shapes and sizes. The cultivar Zinderella Peach (ZP) (Fig. 2B) produces a “scabiosa-type” bloom, with a single row of petals topped with a frilly double row of petals (Trinklein 2015). It can also produce “single blooms” (Fig. 2A) that have flat, circular flower heads with petals arranged in a single row (Maughan et al. 2020). Other cultivars, such as Benary’s Giant Purple (BGP) (Fig. 3A) and Oklahoma Ivory (OI) (Fig. 4), produce “double blooms” with multiple rows of petals, causing the flower head to have a somewhat “domed” shape (Ali et al. 2021; Maughan et al. 2020).
Queen Red Lime cultivar grown in this study. The bloom shows bicolored coloration, with green petals near the center, and red petals near the outside of the bloom.
Citation: HortTechnology 34, 5; 10.21273/HORTTECH05452-24
Zinderella Peach (ZP) cultivar grown in this study. (A) The “single bloom” with petals arranged in a single row, creating a flat, circular appearance to the bloom. (B) The “scabiosa-type” bloom with one row of petals topped with a frilly double-blooming row of petals common to this cultivar. (C) A fully developed ZP single bloom zinnia ready for harvest with one full row of petals fully expanded. (D) ZP falling into the nonmarketable insect damage category. (E) An example of ZP falling into the nonmarketable curved stem category. (F) An example of a ZP falling into the other defects category (this example depicts deformed petals).
Citation: HortTechnology 34, 5; 10.21273/HORTTECH05452-24
Benary’s Giant Purple (BGP) cultivar grown in this study. (A) Petals arranged in multiple rows, called a “double bloom,” creating a fuller, more domed look to the blooms. (B) depicts a fully developed BGP zinnia (double bloom) ready for harvest with at least two rows of petals fully expanded.
Citation: HortTechnology 34, 5; 10.21273/HORTTECH05452-24
Oklahoma Ivory cultivar grown in this study, showing petals arranged in multiple rows, called a “double bloom,” creating a fuller, more domed look to the bloom.
Citation: HortTechnology 34, 5; 10.21273/HORTTECH05452-24
Zinnias require full sun and well-drained soil, as well as 1 to 1.5 inches of water two to three times per week during establishment, then reduced to 1 to 1.5 inches one to three times per week during the growing season (Maughan et al. 2020). Given the general lack of trees or shade in eastern South Dakota, along with the deep, well-drained Houdek Loam soil present in the eastern half of the state, the climatic and soil conditions in eastern South Dakota align with those required of zinnia cut flower production. However, this region receives inconsistent rainfall (US Department of Agriculture, Natural Resource Conservation Service 2023), indicating that zinnias grown in this region need to be irrigated to have consistent access to water.
A 2-year trial of zinnias was conducted to quantify the number and quality of stems produced by four commercially available cultivars of zinnias. This study aimed to increase research and support for the region’s local cut flower farmers.
Materials and methods
Site description
The zinnia trial was conducted at the South Dakota State University Specialty Crop Research Field, located in Brookings, SD, USA at ∼44°19′18″N, 96°46′21″W, at an elevation of 496 m. It is classified under US Department of Agriculture hardiness zone 4, with an average last frost date of 12 May and an average first frost date of 21 Sep. The soil is a Barnes clay loam with a land capability class of one. This study took place during the summers of 2022 and 2023, and production was evaluated in unprotected field conditions in both years.
Zinnias were grown in a randomized complete block design in four beds that were each 48 feet long by three feet wide. Each bed was divided into four blocks and each block contained four randomized plots. Each plot contained a single cultivar of zinnia. Zinnias in each plot were spaced 9 inches apart in a three-row grid for a total of nine plants per plot. The four zinnia cultivars chosen for this study were the commercially available cultivars ZP, BGP, OI, and QRL (Johnny’s Selected Seeds). These cultivars were chosen to represent a variety of colors and bloom types that are of interest to growers in the region.
Greenhouse production
In 2022, zinnias were seeded into 72-cell trays (The Tessman Company, Tea, SD, USA) using Promix Organic Vegetable and Herb Mix (Premier Tech, Rivière-du-Loup, QC, Canada) on 26 Apr. Temperatures in the greenhouse were set to range from 65 to 75 °F, and the actual temperature range was 58.8 to 89.3 °F, with an average of 71.3 °F. Relative humidity was set at 40% to 80%, and the actual range was 11.6% to 99.8% with an average of 59.7%. Four hundred watt high-pressure sodium lights were used from 6:00 AM to 10:00 PM daily. Seedlings remained in the greenhouse until the last week of May, after which they were placed outside to harden off. They were pinched to two nodes in the greenhouse on 25 May before transplanting to encourage more branching. Due to cool soil temperatures and wet conditions at the end of May, zinnia planting was delayed, and the seedlings were transplanted in the field on 6 Jun.
In 2023, zinnias were seeded on 10 Apr using the same methods as just described. The temperature and humidity were set to the same ranges as the previous year (65 to 75 °F and 40% to 80% relative humidity). Temperatures in the greenhouse ranged from 60.2 to 98.3 °F with an average of 71.2 °F. Relative humidity ranged from 16% to 99.8% with an average of 65.9%. The same 400-W high-pressure sodium lights from the previous year were used from 6:00 AM to 10:00 PM daily. The seedlings remained in the greenhouse until the first week of June when they were removed to harden off. Unlike the previous year, zinnias were pinched once in the greenhouse (on 22 May) before transplanting and twice in the field (on 15 Jun and 25 Jul). Planting was also delayed in 2023, and zinnias were transplanted into the field on 15 Jun. Due to the late planting date, the transplants were root bound.
Field preparation
Before zinnias were transplanted into the field, each of the four beds were covered with 3-oz woven black landscape fabric with ultraviolet inhibitor (The Tessman Company). Each 3′ × 300′ roll of landscape fabric was burned into 48-foot-long strips to achieve the correct length and to cauterize the edges. A template was used to burn holes in a 9-inch grid, resulting in three parallel rows of holes in each piece of fabric for the length of the bed.
In 2022, each bed was tilled using a BCS 739 walk-behind tractor (BCS, OR City, OR, USA) with two passes at a 6-inch depth. Two lines of drip tape (The Toro Company, Bloomington, MN, USA) were then laid 16 inches apart over the tilled beds. Tillage and drip tape installation both occurred on 1 Jun followed by fabric installation on 2 Jun. Fabric was secured with six-inch staples (The Tessman Company). A horizontal nylon trellis (3-feet-wide with six-inch grid; Hortnova FA, Tenax US, Baltimore, MD, USA) was installed to support the flower stems, provide some protection from South Dakota winds, and improve stem quality. The trellis was set a few nodes below most of the blooms and moved up as needed throughout the season as the plants grew.
In 2023, the planting area was irrigated before tillage because dry conditions caused the soil to become hard and compact. The beds were tilled with three passes and then soaked a second time to soften the compacted ground further and encourage easier fabric installation. Fabric was installed using the same procedure as the previous year. After the fabric was installed, two lines of drip tape were put into place, spaced 18 inches apart on top of the fabric. Tillage, fabric installation, and drip tape installation all took place on 15 Jun 2023. No trellis was used in 2023.
Irrigation and fertility
In both 2022 and 2023, zinnia seedlings were irrigated in the greenhouse every other day from the day of seeding until they were moved outside. The seedlings were hardened off outside for about 1 week, and during this time they were irrigated one to two times every day, depending on temperature. To meet the water requirements for zinnias once in the field, it was estimated that the plants would need ∼1 to 1.5 inches of water per week. It was calculated that the run time per week for the drip irrigation was ∼6.3 h. To achieve these 6.3 h of watering every week, the irrigation was run for ∼2 to 3 h at a time, 2 to 3 times per week. Under rainy conditions, irrigation was reduced according to the amount of rain received.
In 2022, zinnias were fertilized using a Dosatron fertilizer injector (Ingersoll Rand, Davidson, NC, USA) with Nature’s Source Organic Plant Food 10–1.76–2.49 and 3–0.44–0.83 (Nature’s Source, Sherman, TX, USA). They were fertilized with 10–1.76–0.83 at a rate of 250 ppm N seven times between 8 May and 1 Jul. The rate was increased to 300 ppm N on 25 May. On 3 Jun 2022, before field planting, the zinnia beds were fertilized via drip irrigation for 1 h, and zinnia seedlings were fertilized in the holding area. Near the middle of the growing season, zinnias were fertilized with 3–0.44–0.83 at a rate of 250 ppm N on 15 Aug and 31 Aug.
In 2023, zinnias were fertigated in the greenhouse using a Dosatron with 3–0.44–0.83 at a rate of 100 ppm N five times between 23 Apr and 1 May. The rate was then increased to 200 ppm N for five applications between 2 May and 11 May, and the rate was increased once more to 250 ppm N for six applications between 15 May and 7 Jun. Before field planting and fabric installation, each zinnia bed in the field was broadcast fertilized by hand with Sustane 8–0.88–3.32 medium-grade (Sustane Natural Fertilizer Inc., Cannon Falls, MN, USA) at a rate of 52 lbs N/acre. The general recommendation from Maughan et al. is 65 lbs N/acre (Maughan et al. 2020); however, the actual rate used in this study was reduced from the recommended rate based on soil test results. Each of the four 48-foot beds received 2.23 pounds of fertilizer. The zinnias were fertigated in the field using the Dosatron with 10–1.76–2.49 at a rate of 250 ppm N on 2 Aug and 18 Aug.
Data collection
Stand counts
Stand counts were taken on 7 Jul 2022 and on 2 Aug and 19 Sep 2023 by counting the number of surviving zinnia plants within each plot.
Harvest
Harvest of zinnias began on 7 Jul 2022, and on 2 Aug 2023, with one harvest event occurring weekly until 21 Sep 2022, and 4 Oct 2023, respectively. There were 12 harvest events in 2022 and 10 harvest events in 2023.
At each harvest event, zinnias were harvested when they were “fully developed” (Maughan et al. 2020), defined as “at least two full rows of petals expanded and a mostly stiff upper stem” (Fig. 3B) (Maughan et al. 2020). ZP only had one row of petals, so flowers were harvested when one row was fully expanded and the upper stem was mostly stiff (Fig. 2C). Each fully bloomed zinnia was harvested using clean pruners by snipping the stem at a 45° angle where it branched off from the base of the plant.
Once the zinnias were harvested, flowers from each plot were divided into categories of marketable and nonmarketable based on the quality of the bloom. Flowers were considered marketable if they showed no bloom defects (missing, wrinkled, damaged, or shriveled petals) and had straight, strong stems. The nonmarketable flowers were sorted into categories of “insect damage” (Fig. 2D), “curved stem” (Fig. 2E), and “other defects” (Fig. 2F). The marketable flowers were sorted into categories based on stem length from the top of the bloom to the bottom of the stem. The categories for stem length of marketable blooms were “18+ inches,” “13 to 17.9 inches,” “8 to 12.9 inches,” and “<8 inches” and were based on the categories used by Utah State University. (Maughan et al. 2020). Stems were considered nonmarketable if they were shorter than 8 inches in 2022 or 13 inches in 2023.
Bloom diameter
In 2023, bloom diameter data were collected by taking three stems from either of the marketable stem length categories (13 to 17.9 inches and 18+ inches) and measuring the diameter of the bloom. Diameters were measured to the nearest ¼ inch.
Data analysis
A two-way analysis of variance (ANOVA) was used to analyze the zinnia marketable and nonmarketable categories (2022 and 2023) and bloom diameter (2023). In each ANOVA, cultivar, year, and their interaction were fixed effects. PROC GLIMMIX of SAS/STAT 15.1 was used for all data analysis (SAS Institute, Cary, NC, USA).
In most marketable and nonmarketable harvest categories there were cultivar × year interactions, so data from each year was analyzed independently (Table 2). Means separation was performed on response variables for marketable and nonmarketable harvest categories and bloom diameter using the Fisher’s protected least significant difference procedure (alpha = 0.05).
Results
Climate
The climate data for the 2022 and 2023 growing seasons was collected by a Mesonet network weather station located approximately one-quarter mile from the field (Table 1). In 2022, the maximum air and soil temperatures during the zinnia growing season (June–September) occurred in July, and the minimum occurred in September (Table 1). The average air temperature for the 2022 zinnia growing season was 72 °F, and the average soil temperature was 74 °F (Table 1). There were 37 d in the 2022 growing season in which air temperatures exceeded 90 °F. Brookings received 14.39 inches of precipitation throughout the growing season (March–October), with 8.22 inches of precipitation falling within the zinnia growing season (Table 1).
Climate data in eastern South Dakota from 2022 and 2023 collected by Mesonet.
In 2023, the maximum air temperature during the zinnia growing season (June–September) occurred in both June and August, whereas the minimum occurred in September (Table 1). Soil temperature data were not taken after July; however, the maximum soil temperature recorded occurred in June and July and were nearly identical, whereas the minimum occurred in June (Table 1). The average air temperature during the zinnia growing season was 70 °F, and the average soil temperature was 77 °F (Table 1). There were 18 d in the 2023 growing season in which air temperatures exceeded 90 °F. Throughout the entire growing season (March–October), Brookings received 11.89 inches of precipitation, with 6.39 inches falling within the zinnia growing season (Table 1).
Stand counts
Data were not analyzed for stand counts. Plant survival was similar between years and among cultivars. Almost all plants survived in both years and in all cultivars.
Marketable harvest
In 2022, QRL produced the highest number of marketable stems, followed by ZP, then OI, then BGP (Table 2). BGP and QRL had a trend of higher marketable stem production in the beginning of the season, whereas OI and QRL trended toward more stems later in the season (Fig. 5). In 2023, OI produced the most marketable stems overall, followed by QRL, then ZP, then BGP (Table 2). OI and QRL had a production trend of more marketable stems throughout the entire growing season (Fig. 5).
Average number of stems per plant collected for each marketable category and nonmarketable category during harvest events in 2022 and 2023 of four Zinnia cultivars: Benary’s Giant Purple (BGP), Queen Red Lime (QRL), Oklahoma Ivory (OI), and Zinderella Peach (ZP). Harvest took place 12 times in 2022 with weekly harvests beginning 7 Jul and ending 21 Sep, and 10 times in 2023 with weekly harvests beginning 2 Aug and ending 4 Oct.
The number of marketable (<8 inches) stems harvested from each cultivar (n = 9 plants) during each harvest event throughout 2022 (A) and 2023 (B). ZP = Zinderella Peach; BGP = Benary’s Giant Purple; QRL = Queen Red Lime; OI = Oklahoma Ivory.
Citation: HortTechnology 34, 5; 10.21273/HORTTECH05452-24
In 2022, QRL and BGP produced the most ≥18-inch marketable stems (4.48 and 3.78, respectively) producing an average of 3.09 more stems per plant compared with ZP, which produced the lowest number of stems in this category (1.04) (P < 0.0001) (Table 2). In 2023, BGP again had the highest number of ≥18-inch marketable stems (1.90), producing an average of 1.62 more stems per plant than the lowest producing cultivar, ZP (0.28), but production tapered off for QRL (1.39), OI (0.98), and ZP (0.28) (P < 0.0001) (Table 2).
In both 2022 and 2023, OI produced the largest number of 13- to 17.99-inch-long stems (7.33 and 3.96, respectively), producing an average of 4.15 (2022) and 2.63 (2023) more stems per plant than the lowest producing cultivar, BGP (3.18 in 2022 and 1.33 in 2023) (Table 2). In 2022, ZP produced the second highest number (6.04), followed by QRL (4.99), but in 2023, the response of ZP (2.33) and QRL (2.91) was flipped (P < 0.0001) (Table 2).
For the 8- to 12.99-inch-long category, in 2022 ZP produced the most stems (9.01), producing an average of 4.89 more stems per plant than the lowest producing cultivar, BGP (4.12), in this category (P < 0.0001) (Table 2). In 2023, both OI and ZP produced the most 8 to 12.99-inch-long stems (1.96 and 1.75, respectively), producing an average of 1.45 more stems per plant compared with BGP (0.41) (P < 0.0001) (Table 2). In 2022, QRL produced the second largest number (7.06), followed by OI (5.71), whereas in 2023, QRL produced the second largest number of stems (1.06) (P < 0.0001) (Table 2), with BGP producing the fewest stems in this category in both years (P < 0.0001) (Table 2).
Nonmarketable harvest
In 2022, ZP produced the most <8-inch-long, nonmarketable stems (10.75), with an average of 9.96 more stems per plant than the lowest producing cultivar in this category, BGP (0.79) (P < 0.0001). Production tapered off for OI (8.81) and QRL (2.85) (P < 0.0001) (Table 2). In 2023, ZP (0.37) and OI (0.24) produced the largest number of <8-inch-long stems, producing an average of 0.25 more stems per plant than QRL (0.09) and BGP (0.03) (P = 0.0004) (Table 2). OI and QRL were not statistically different from each other, but OI was different from BGP (P = 0.0004) (Table 2).
For the curved stem category, ZP and BGP produced the largest number of curved stems in 2022 (0.47 and 0.44, respectively), with an average of 0.28 more curved stems per plant than OI (0.21) and QRL (0.14) (P = 0.0019) (Table 2). In 2023, BGP and OI produced the largest number of curved stems (2.83 and 2.39, respectively), producing an average of 3.37 more curved stems per plant than QRL (1.98) and ZP (1.73) (P = 0.0002). QRL and ZP were not statistically different from each other (Table 2).
There was not enough data collected for the insect damage category in 2022 for effective data analysis due to lower standards for what was considered a “marketable” bloom. In 2023, the ZP cultivar had the most insect damage (2.66), with an average of 1.61 more stems per plant falling into this category than the lowest producing cultivars, BGP (1.24) and OI (0.87). (P < 0.0001) (Table 2). QRL (1.64) and BGP had less damage, and BGP and OI, which were not statistically different from each other, showed the least amount of insect damage (Table 2).
In 2023, the ZP cultivar had the largest number of stems showing other defects that were not covered by the other three nonmarketable categories (9.08), producing an average of 4.81 more defective stems per plant than BGP (4.27), which produced the lowest number of stems with other defects (P < 0.0001) (Table 2). Production of stems with other defects tapered off for QRL (6.84) and OI (6.26) but remained greater than BGP (P < 0.0001) (Table 2).
Bloom diameter
Bloom diameter was only collected in 2023. BGP produced the blooms with the largest diameter (3.09 inches), QRL produced the second largest bloom diameters (2.32 inches), and OI and ZP produced the smallest bloom diameters (2.02 and 2.07 inches, respectively) (P < 0.0001) (Fig. 6).
The average bloom diameter of each cultivar in 2023. Letters showing statistical significance are compared. BGP = Benary’s Giant Purple; QRL = Queen Red Lime; OI = Oklahoma Ivory; ZP = Zinderella Peach.
Citation: HortTechnology 34, 5; 10.21273/HORTTECH05452-24
Discussion
‘Zinderella Peach’
In both 2022 and 2023, ZP produced the lowest number of marketable stems by the end of the growing season. This may have been due to the high temperatures (>90 °F) occurring in both growing seasons. For the ZP cultivar, several growers in cooler climates have reported higher levels of success with marketable stem production than those growing in hotter, drier climates (The Kokoro Garden 2019). Several growers have also reported this cultivar as being inconsistent in the production of marketable blooms (National Gardening Association 2024). The low number of ≥18-inch-long marketable stems is consistent with the plant height because the ZP plant tends to be shorter than the other cultivars grown in this study (Johnny’s Selected Seeds 2024).
For each nonmarketable category, ZP produced a greater number of stems compared with the other cultivars. In the <8-inch-long stem category, the high number of stems produced may be due to its short plant height (Johnny’s Selected Seeds 2024). ZP also showed the most insect damage, which is consistent with prior work that found that the Zinderella series showed the most insect visitation compared with all other cultivars, potentially due to the high proportion of central disk florets found on this type of bloom (Merrell et al. 2021). While the insects observed by Merrell et al. were mainly pollinators, it may be possible that both beneficial and detrimental insects prefer ZP over other zinnia cultivars.
ZP produced the highest number of stems with other defects compared with all the other cultivars. Previous work found similar results for the Cupcake series, which has a similar “scabiosa-type” bloom (Maughan et al. 2020). The researchers speculated that Cupcake had high cull rates and short stems due to transplant and heat stress (Maughan et al. 2020). Given that high temperatures were observed in eastern South Dakota in both 2022 and 2023, it is possible that heat stress may have caused ZP to revert to single blooms, producing fewer marketable flowers in this study.
The production of curved stems in the ZP cultivar varied between years, with high numbers in 2022 and low numbers in 2023. One potential reason for this difference between years could be the use of the trellis in 2022. The trellis was set up to support the taller flowers and promote straight stems (Maughan et al. 2020); however, it left the shorter stems unsupported in the shorter cultivars. Because ZP produced the shortest stems, it received the least amount of support from the trellis, resulting in the highest number of curved stems among all the cultivars. In 2023, no trellis was used, so the taller cultivars did not receive as much support as they did in 2022. This underscores the importance of adequately trellising both taller and shorter zinnia varieties.
In our research, the bloom diameter of ZP was consistent with the advertised average bloom sizes of these cultivars at 2 to 2.5 inches (Johnny’s Selected Seeds 2024).
‘Oklahoma Ivory’
OI had the highest number of marketable stems among all cultivars, which was consistent with multiple field trials and reports that state that the OI cultivar tends to have high yields over a long period of time (Coker and DelPrince 2022; NC State Extension 2021). OI produced the second lowest number of ≥18-inch-long marketable stems in both 2022 and 2023, which is consistent with its average plant height as the second shortest cultivar grown in this study (Johnny’s Selected Seeds 2024); however, similar to ZP, stem production in each of the subsequent marketable categories increased compared with the number of stems in the ≥18-inch-long category.
Results for OI in each of the nonmarketable categories remained about average compared with the other cultivars. Overall, OI tended to produce higher numbers of stems in the shorter stem categories, which is consistent with plant height, as OI was the second shortest cultivar in this study (Johnny’s Selected Seeds 2024). OI showed low amounts of insect damage compared with the other cultivars. This may have been due to the presence of ZP, which was more attractive to insects. One study found that double flowers such as OI may be more difficult for insects to pollinate due to the obstruction of the disk florets by the ray florets (Miyajima 1995). Due to this obstruction, it is possible that the OI cultivar was less attractive to insects than other cultivars and so received less damage in this study.
The production of curved stems by the OI cultivar varied between the 2 years, with lower numbers in 2022 and higher numbers in 2023. This increase from the 2022 to 2023 growing seasons is likely due to the absence of the trellis in 2023. The stems were supported in 2022 but not in 2023, resulting in a higher number of curved stems in 2023.
OI produced a low number of stems with other defects. This is consistent with most findings indicating that the Oklahoma series has minimal problems and defects and produces large numbers of marketable double blooms (NC State Extension 2021).
For bloom diameter, OI produced one of the smallest blooms overall and is consistent with the advertised average bloom sizes of 1.5 to 2.5 inches for this cultivar (Johnny’s Selected Seeds 2024).
‘Queen Red Lime’
In both 2022 and 2023, QRL produced the second largest number of marketable stems. This is consistent with previous work, which found that QRL had “moderate yields,” producing acceptable numbers of marketable stems but not as many as other cultivars (Maughan et al. 2020). In both years of this study, QRL produced high numbers of marketable ≥18-inch-long stems compared with all other cultivars but produced fewer stems in the shorter categories and had lower overall yield. This was likely due to the plant height because QRL had the second-tallest advertised plant height of the cultivars grown in this study (Johnny’s Selected Seeds 2024). The numbers of shorter marketable stems produced by QRL remained about average compared with the other cultivars. This also may have been due to the tall plant height and the “moderate yields” associated with the QRL cultivar.
In the curved stems category, QRL produced much longer stems than both the ZP and OI cultivars but had fewer curved stems compared with all cultivars despite not having the support of the trellis in 2023. This is consistent with the findings of several growers who found that the Queen series tends to comprise “sturdy, compact plants” (All-America Selections 2018), that have stronger stems than other cultivars. This may mean that QRL can better withstand the strong South Dakota winds while still producing straight, sturdy stems.
For the insect damage category, QRL showed less damage than ZP, but more than other cultivars. Although QRL produces double blooms that may be less attractive to insects, one previous study found that QRL had the highest number of anthers of all the cultivars in their trials (Merrell et al. 2021). This may cause QRL to be more attractive to both pollinators and insect pests, which would account for the higher levels of insect damage seen in this cultivar. QRL also produced large numbers of stems with other defects. Similarly to ZP, QRL tends to be inconsistent with bloom quality and color, which may contribute to the higher numbers of stems with other defects (Dole et al. 2014).
For bloom diameter, QRL produced the second largest blooms, which is consistent with its advertised average bloom diameter of 2 to 3.5 inches (Johnny’s Selected Seeds 2024).
‘Benary’s Giant Purple’
In both years, BGP produced fewer marketable stems compared with the other three cultivars; however, the number of marketable stems produced was higher at the beginning of the 2022 harvest than in 2023. This is consistent with previous findings that showed that the Benary’s Giant series was less prolific than other series that produced smaller blooms (Maughan et al. 2020), and planting time greatly affects the number of stems produced per plant (Sloan and Harkness 2008). The difference in planting date between the 2 years may explain the difference in the number of marketable stems produced at the beginning of the harvest season in 2022.
Although BGP produced fewer marketable stems overall, in both years BGP produced large numbers of ≥18-inch-long stems. This is consistent with plant height because BGP was the tallest cultivar grown in this study (Johnny’s Selected Seeds 2024). The number of stems produced by BGP in each of the subsequent marketable categories decreased, which was likely a result of the tall plant height and large numbers of ≥18-inch stems.
Results for the nonmarketable categories varied for BGP, depending on the category. BGP produced the lowest number of short stems, which may be explained by the tall plant height of this cultivar. Despite the presence of the trellis in 2022, BGP was among the cultivars that produced the highest number of curved stems in both years. The similar results between the 2 years may have been due to the height of the trellis, which was set up to support as many flower stems as possible. However, the BGP stems were much taller than the other three cultivars and may have been too tall for the trellis to provide the support needed to prevent the formation of curved stems in 2022, resulting in large numbers of curved stems in both years, regardless of the presence of the trellis.
For the insect damage category, BGP showed low amounts of damage. Because BGP produces double blooms, it is less attractive to pollinators (Merrell et al. 2021). It may also be less attractive to pest insects, which would explain the lower number of insect-damaged blooms in this study. BGP also produced lower numbers of stems with other defects, which is consistent with many other reports stating that the Benary’s Giant series consistently produces high-quality blooms (Maughan et al. 2020; NC State Extension 2021).
BGP had the largest bloom diameter compared with all the other cultivars, which is consistent with its advertised average bloom diameter of 4 to 6 inches (Johnny’s Selected Seeds 2024).
Overall, in this study, the cultivars that produced the best total number of marketable stems were QRL in 2022 and OI in 2023. The best cultivars for each marketable category were the cultivars that produced the highest numbers in each category and are as follows: BGP for ≥18-inch-long stems, OI for 13- to 17.99-inch-long stems, and ZP for 8 to 12.99-inch-long stems in 2022 (this category was considered marketable in 2022 but nonmarketable in 2023). The reason for the lower number of marketable stems overall in 2023 compared with 2022 was because the marketable flowers were sold in 2023 but not in 2022. This created a higher standard for what was considered a “marketable” bloom in 2023 compared with 2022.
The best cultivars for each of the nonmarketable categories in this study are the cultivars that produced the lowest numbers of nonmarketable stems and are as follows: BGP for 8- to 12.99-inch-long stems in 2023, BGP for <8-inch-long stems, QRL for curved stems, BGP and OI for insect damaged stems, and BGP for stems with other defects. BGP was the best cultivar in this study for bloom diameter, producing the largest blooms overall.
Conclusion
BGP should be considered for use on Midwest flower farms where growers prioritize flowers with long stems and large blooms with minimal defects and less susceptibility to insect damage. Midwest flower farmers who prioritize straight, sturdy stems of marketable length and medium bloom size should consider QRL. OI and ZP did not perform as well as the other two cultivars in this study; however, Midwest flower farmers who prioritize large numbers of smaller blooms with minimal insect damage should consider OI. Those who are particularly concerned about curved stems and want a unique variety of zinnia may want to consider ZP. This study sets the stage for a continuation of cut flower trials across the Midwest as farmers and researchers collaborate to improve cut flower systems in the expanding local flower market.
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