Hort. Series # 249

 

Principal Investigators: Jonathan R. Schultheis, Professor and Extension Specialist, Department of Horticultural Science, NC State University; Stuart W. Michel, Research Technician, Department of Horticultural Science, NC State University; Brandon K. Parker, Research Associate, Department of Horticultural Science, NC State University; Baker E. Stickley, Research Assistant, Department of Horticultural Science, NC State University.

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Acknowledgements

We gratefully acknowledge the assistance of Hunter Barrier (Superintendent) and Wesley Hairre (Horticulture Supervisor), Horticultural Crops Research Station, Clinton, NC, as well as the personnel at the research station for their help in establishing, maintaining, and harvesting the 2025 cultigen evaluation study. We want to acknowledge summer employees Ariana Phouangkeo, Cameron Roberts, Dylan Orechovesky, and Isabella Johnson for their assistance with this study. The cooperation and support of Enza Zaden, HM Clause, Known You Seed, Origene Seeds, Rijk Zwaan, Seedway, and Syngenta were also appreciated. We also want to thank Joy Smith for performing the statistical analysis and aiding in the interpretation of the data collected from this study.

Disclaimer

This publication presents data from the standard size triploid watermelon cultigen evaluation study conducted during 2025. Information in this report is believed to be reliable but should not be relied upon as a sole source of information. Limited accompanying detail is included but excludes some pertinent information, which may aid interpretation. 

Financial Support

In addition to seed companies, this research was supported by the College of Life and Agricultural Sciences, North Carolina Agriculture Research, the North Carolina Cooperative Extension Services, and the North Carolina Department of Agriculture and Consumer Services. This work was in part supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2020-51181-32139.

Introduction

Watermelon production in North Carolina totaled 10,700 acres harvested in 2024 and was valued at approximately $35.8 million. Acreage has increased from 9,600 acres in 2023, however the price per unit (cwt) has decreased from $15.80 in 2023 to $14.1 in 2024 resulting in a net reduction of production value of $13.6 million during the same time (NC Ag Stats).

Nationally, consumer demand for whole standard watermelon has decreased by 0.3% from 2023-24 to 2024-25. From 2024-2025, whole standard watermelon accounted for 78.5% of all watermelon sales in the U.S. In the Southeast, whole standard watermelon demand decreased 2.9%. However, for North Carolina, retail scanner data shows that the Raleigh/Greensboro area had a 2.7% increase in sales and the Charlotte area had a 2.5% increase in sales (Watermelon Retail Scan Data).

In 2025, Dr. Schultheis and the Cultural Management Program in the Horticulture Department at NC State University conducted an evaluation of 20 standard size triploid (seedless) cultigens from 7 seed companies at the Horticultural Crops Research Station in Clinton, NC. The watermelon entries were evaluated for yield and quality characteristics such as soluble solids (sweetness or Brix), color, firmness, and hollow heart. The methods, results, and representative photos from the study are presented below.

 

Materials and Methods

Sowing and Field Preparations

Once all seeds were received from participating companies, they were planted into 72-cell poly trays to grow transplants (Hummert Int.; Earth City, MO). The watermelons seeds were sown on 25 March 2025. The trays of sown seeds were placed in a germination room for 48-72 hours, once 30-40% of seeds in each tray had germinated. Temperature in the germination room was kept between 85-90°F and humidity was kept between 85-90%. The planting medium used was a ‘fine germinating mix’, a commercial soilless mix (SunGro, Agawam, MA). After germination, transplants were moved to a greenhouse set to 85°F and hand watered twice daily. The seedlings were fertilized at least once a week with 20-10-20 water soluble fertilizer at a rate of 200-250 ppm.The field planting site was located at the Horticultural Crops Research Station in Clinton, NC. The watermelons were planted in blocks R5 and R10; a Norfolk and Orangeburg Loamy Sand type soil. Granular fertilizer (10-10-10 at 500 lb/ac and 0-0-21-21 at 200lb/ac) was applied broadcast on 3 April 2025. Pic 60 (29 gal/ac) was sprayed to fumigate the study area on 15 April 2025 for weed and nematode control. Black polyethylene plastic (1.25 mil thick, high density plastic film, 54 inches wide; TriEast Ag Group, Inc., Clinton, NC) was laid on 15 April 2025.

Transplanting and Vine Training

The triploid (seedless) watermelon transplants were established in the field on 5 May 2025. Plot size for the standard size watermelons was 1 row, 10 triploid plants per row with an additional 4 pollenizers, 35 feet long with alleys of 10 feet between plots. Row middles were 10 feet and in-row spacing was 2.5 feet. Stand counts were taken one week after planting with no plants needing to be replaced. ‘SP-7’ and ‘Wingman’ (4 plants/plot) were used as the pollenizer plants in this study. ‘SP-7’ pollenizers were planted after triploid plants 1 and 7 while ‘Wingman’ pollenizers were planted after triploid plants 4 and 10 in each plot, maintaining 2.5 foot in-row spacing. Once vines had grown over the plastic mulch, they were gently turned/trained back into the plot each week. This aided harvest and data collection by avoiding mixing cultigens and reducing vine damage at harvest.

Fertilizer and Pest Management

A total of 50 lb/ac N, 50 lb/ac P, 92 lb/ac K, 42 lb/ac S, and 20 lb/ac Mg were all applied broadcast (pre-plant) to the entire study area. Drip tape (NETAFIM, 12 in spacing, 0.24 gph; NETAFIM, Tel Aviv, Israel) was installed beneath the black plastic mulch to fertigate the crop throughout the growing season. Liquid fertilizer with 4-0-8 analysis was applied through drip tape fertigation 15 times at rates of 20, 25, or 35 gal/ac, and a final fertigation at a rate of 8.41 gal/ac. Cumulative totals, pre-plant and through the drip tape, of applied fertilizer nutrients were: 183.87 lb/ac N, 50 lb/ac P, and 359.75 lb/ac K.

Herbicides (Table 1), insecticides (Table 2), and fungicides (Table 3) were applied as needed and as directed by the label for that crop (2025 NC Ag Chem Manual), along with adjuvants and surfactants as necessary (Table 4). Different products were rotated in the next application to avoid potential development of resistance.

 

Weather

Weather was favorable during the growing season, with no considerable periods of drought or flood conditions in the area of the study. A total of 16.32 inches of rain occurred at the field planting site in Clinton, NC throughout the duration of the study. Most of the rainfall occurred from transplant to harvest, with limited rainfall during the harvest season. High temperatures generally exceeded 90 °F from late June through harvest, with temperatures typically exceeding 70 °F.

Study Design and Data Collection

The study used a randomized complete block design with four replications. There were a total of 4 harvests collected over 21 days (9 July through 30 July) with some harvests spanning 2-3 days. Fruits were picked when signs indicated they were ripe; yellow to tan ground spot, dead tendrils, ribbing, color. Fruits were counted and weighed individually. Fruit with pest damage and or rot were weighed and counted if the fruit was intact and representative of the rest of the plot. Vines were moved to cover unpicked fruit to minimize the occurrence of sunscald at later harvests.

Quality Evaluations

Measurements were taken on 12 fruit (3 per replication) of each cultigen to determine the fruit size, fruit shape, soluble solids (sweetness or Brix), interior flesh firmness, flesh color, rind thickness, seed trace size, hard seed population, and hollowheart. The most representative fruit were selected for quality measurements and measurements were retaken on another fruit if necessary. Soluble solids were measured by cutting a piece of flesh from the center of the fruit and squeezing out the fruit juice onto the digital refractometer (Atago, Vernon Hills, IL). Flesh firmness was taken using a Penetrometer FT 011 with a 7/16’ plunger tip (QA Supplies LLC, Norfolk, VA), and was recorded in pounds. Samples were obtained by cutting the center of the fruit from the stem to blossom end. Pressure was then taken in five areas of the fruit: stem end, top side, ground spot side, blossom end, and center. The reported measures on flesh firmness are an average of the five sample areas. Hard seed in triploid fruit was determined according to the USDA standards. Fruits were cut longitudinally in half, halves were cut longitudinally once more, and one quarter was cut laterally. The number of hard seeds exposed on the cut surface were counted and recorded. Most of the quality measurements were taken in the first harvests (1-2). Additional information on the quality measurements is presented in the Quality section on pages 9-11, Tables 9 and 10.

Results and Discussion

Consistent precipitation, and favorable temperatures resulted in considerable improvement in yields when compared to previous years.For the analysis, fruits were placed in the following size categories: < 9 lb, 9-13.4 lb (60 count bin), 13.5-17.4 lb (45 count bin), 17.5-21.4 lb (36 count bin), and ≥ 21.5 lb (30 count bin). The yellow flesh cultigen ‘Buttercup’ from Seedway as well as two popular red flesh cultigens, ‘Fascination’ from Syngenta and ‘Cracker Jack’ from Enza Zaden, were included as comparisons. Fruit below 9 lb was considered unmarketable for the standard watermelon category.

Cumulative Harvests (1-3)

Yield: Cwt per acre

The cultigen ‘Red Amber’ from Enza Zaden had the highest marketable yield of all 20 entries in this study at 1036.7 marketable hundred-weight per acre (Mkt. cwt/ac) (Table 5). ‘Troubadour’ from HM Clause had the second highest marketable yield at 983.8 Mkt. cwt/ac. The average marketable yield across all 31 cultigens was 777.6 cwt/ac. Popular cultigens ‘Cracker Jack’ and ‘Fascination’ had marketable yields of 717.7 cwt/ac and 944.4 cwt/ac, and were ranked 15th and third, respectively.

 

Yield: Number of fruit per acre

‘Troubadour’ from HM Clause had the highest number of marketable fruit per acre (Mkt no/ac) at 6708 (Table 6). ‘Buttercup’ from Seedway produced the second highest number of marketable fruit per acre at 6360. The average number of marketable fruit per acre across all entries was 4924. ‘Cracker Jack’ and ‘Fascination’ had 4792 and 5401 marketable fruit per acre, and were ranked eleventh and sixth, respectively.

‘Troubadour’ from HM Clause also had the highest number of fruit per plant (Fruit no/plant) at 4.4 (Table 6). ‘Buttercup’ from Seedway and ‘Tropical Honey’ from Rijk Zwaan had the second highest number of fruit per plant at 4.3. The average number of fruit per plant across all entries was 3.2.

Yield: Bins per acre

‘Red Amber’ from Enza Zaden was the entry with the highest number of bins with marketable fruit per acre (Mkt bins/acre) across all entries with 148.1 bins (Table 7). Marketable bins does not include fruit in the less than 9 pound category (< 9 lb). ‘Troubadour’ from HM Clause had the second highest number of marketable bins per acre at 140.5 bins. The average number of marketable bins across all entries was 111.1 bins. Cultigens ‘Cracker Jack’ and ‘Fascination’ had 102.5 and 134.9 bins with marketable fruit per acre and were ranked 15th and third, respectively.

 

Yield: Average fruit size and bin size distribution

‘Virtue’ from Syngenta produced the largest average fruit at 18.5 pounds per fruit. ‘Virtue’ had 74.1% of its fruit in the 30 and 36-count bin categories. The average fruit weight across all 20 entries was 15.1 pounds with a range of 18.5 to 10.7 pounds per fruit. Cultigens ‘Cracker Jack’ and ‘Fascination’ had average fruit weights of 14.2 and 17.1 pounds per fruit, and were ranked 15th and second, respectively.

‘Virtue’ also had the highest percentage of fruit in the 30-count bin category at 46.4% followed by ‘Black Jack’ at 35.3% (Table 8). ‘Big Jack’ from Seedway had the highest percentage of fruit in the 36-count bin category at 38.8%. ‘Cracker Jack’ from Seedway had the highest percentage of fruit in the 45-count bin category at 48.3%.

 

Quality

‘Honeycutt’ from HM Clause was the sweetest of all 20 entries, with an average Brix of 13.6 (Table 9). Brix is a measure of sugar content, and the units equate to 1 gram of sucrose in 100 grams of solution. ‘Big Jack’ from Seedway ranked second for sweetness with an average Brix of 13.2. The average sugar content across all 20 entries was 12.1, with more than half of the entries having an average Brix above 12.0.

The entry with the firmest flesh was ‘Cato’ from Syngenta, with an average firmness of 4.4 pounds (Table 9). Cultigens ‘Cracker Jack’ and ‘Fascination’ had average flesh firmness ratings of 2.4 and 2.7 pounds, respectively.

‘Black Jack’ from Seedway had the highest flesh color ratings of the 14 red-fleshed watermelon entries with an average color rating of 5.0; color is based on a 1 to 5 scale with 1 being pale or white and 5 being a deep blood red (Table 9). Flesh color was good in this study, with an average color rating of 4.5. 6 of the 20 entries produced yellow flesh (Felicity, Festival, Tropical Honey, Sunstone, Buttercup, and Orchid Sweet) and were therefore not rated on a scale of 1 to 5.

‘Tropical Honey’ from Rijk Zwaan had the thinnest rind at 12.8 mm (Table 9). ‘ORS 61229’ from Origene had the thickest rind at 20.1 mm. The average rind thickness across all cultigens was 16.8 mm.

‘Buttercup’ from Seedway had the lowest population of hard seeds with an average 0 hard seeds per fruit (Table 9). ‘Rio Grande’ from Enza Zaden had the highest population of hard seeds at 3.4 seeds per fruit, and the average across all cultigens was 1.3 hard seeds per fruit. All 20 entries had minimal hard seeds.

‘Eleanor’ from HM Clause, and ‘ Buttercup’ and ‘Sunstone’ from Seedway all had the smallest seed trace in the study at a rating of 1.3; seed trace was measured on a 1-5 scale with 1 being small and 5 being large (Table 9). Overall, seed trace size was small across all entries with an average rating of 1.7.

 

Quality: Hollowheart

Half of the cultigens in this study (10 out of 20) had no incidence of hollowheart (Table 10). Of those that did have hollowheart, only five cultigens had any fruit with a rating of 3 or higher; a rating of 3 or 4 are considered unmarketable.

 

Harvest 1: 9 July

Harvest 1 Yield: Cwt per acre

‘Cato’ from Syngenta had the highest marketable yield in the first harvest with 75 cwt/ac (Table 11). ‘Black Jack’ from Seedway was ranked second with 72 mkt. cwt/ac. The first harvest only comprised about 10% of the total marketable weight. The average marketable yield for the early harvest was 44 cwt/ac.

 

Harvest 1 Yield: Number of fruit per acre

‘Tropical Honey’ from Seedway had the highest number of marketable fruit per acre (Mkt no/ac) at 523 (Table 12).  ‘Tropical Sunshine’ from Seedway, ‘Cato’ from Syngenta, and ‘Black Jack’ from Seedway had the highest number of fruit per plant (Fruit no/plant) at 0.3 or 3 fruit for every 10 plants for the early harvest.

 

Harvest 1 Yield: Bins per acre

‘Cato’ from Syngenta had the highest number of bins with marketable fruit per acre (Mkt. bins/ac) for the early harvest at 10.7 bins/ac, (Table 13). The average number of bins with marketable fruit per acre in the early harvest was 6.3 bins per acre.

Harvest 2: 17 July

Harvest 2 Yield: Cwt per acre

‘Red Amber’ from Enza Zaden had the highest marketable yield for the second harvest at 563 cwt/ac (Table 14). ‘Fascination’ from Syngenta ranked second at 458 cwt/ac, and ‘Felicity’ and ‘Festival’, yellow-fleshed watermelons from Known You Seed ranked third at 428 cwt/ac for the second harvest. It should be noted that the marketable yields for ‘Felicity’ and ‘Festival’ would be reduced due to hollowheart incidence. The average marketable yield across all entries was 379.9 cwt/ac for the second harvest.

 

Harvest 2 Yield: Number of fruit per acre

‘Red Amber’ from Enza Zaden had the highest number of marketable fruit per acre for the second harvest at 3311 (Table 15). ‘Tropical Honey’ from Rijk Zwaan ranked second for marketable fruit per acre at 3049 no/ac, and ‘Cracker Jack’ from Seedway ranked third at 2788 no/ac. The average number of marketable fruit across all entries for the second harvest was 2341.4 no/ac.

 

Harvest 2 Yield: Bins per acre

‘Red Amber’ from Enza Zaden had the highest number of bins with marketable fruit per acre for the second harvest at 80.4 bins/ac (Table 16). ‘Fascination’ from Syngenta had the second highest number of marketable bins from the second harvest at 65.4 bins/ac, while ‘Felicity’ from Known You Seed ranked third at 61.2 bins/ac. The average number of marketable bins across all entries in the second harvest was 54.3 bins/ac.

 

Harvest 3: 24 July

Harvest 3 Yield: Cwt per acre

‘Buttercup’ from seedway, had the highest marketable yields in the third harvest with 547 cwt/ac (Table 17). The average marketable yield was 301.8 cwt/ac across all entries for harvest three.

 

Harvest 3 Yield: Number of fruit per acre

‘Buttercup’ from Seedway had the highest numbers of marketable fruit per acre for the third harvest at 3615 (Table 18). There were more fruit overall in the third harvest compared to prior harvests, with an average of 1912.3 fruit per acre. Marketable yield through harvest three remained strong with average marketable fruit per acre across all entries being 1912.3 no/ac.

 

Harvest 3 Yield: Bins per acre

‘Buttercup’ from Seedway had the highest number of bins with marketable fruit per acre for the third harvest, at 78.2 bins/ac (Table 19).  The average number of marketable bins per acre was 45.5 across all entries in the third harvest.

 

Harvest 4: 30 July

Harvest 4 Yield: Cwt per acre

‘Valor’ from Syngenta had the highest marketable yields in the fourth and last harvest with 183 cwt/ac (Table 20). The average marketable yield for the fourth harvest across all entries was 51.8 cwt/ac, which was similar to harvest 1 (Table 11).

Harvest 4 Yield: Number of fruit per acre

‘Valor’ for Syngenta had the highest numbers of marketable fruit per acre for the fourth harvest at 1,350 fruit per acre (Table 21). There were less fruit overall in the fourth and final harvest compared the previous two harvests, with an average of 389.9 fruit per acre. Only the top 6 cultigens during this harvest yielded more than 400 marketable fruit per acre in the late harvest, while the average across all entries in the previous two harvests was 2341.4 and 1912.3 no/ac for harvests two and three, respectively.

 

Harvest 4 Yield: Bins per acre

‘Valor’ from Syngenta had the highest number of bins with marketable fruit per acre for the fourth harvest, at 26.1 bins/ac (Table 22).  The average number of marketable bins per acre was 7.4 across all entries in the latest harvest.