Melon and watermelon production under high tunnels was investigated previously in Missouri (Jett, 2006: High tunnel melon and watermelon production. MU Extension). However, low tunnels and caterpillar high tunnels have the advantage that they are easy to relocate avoiding repeated crops in the same soil and more affordable in the short term. In this article, we provide information from our study that demonstrated that watermelon can be planted under protected production systems (low and high tunnels) in Missouri, early enough to reach the Fourth of July market window with premium prices. Securing a share of the Fourth of July market may increase the sustainability of small and medium-size specialty crop farmers in Missouri, especially those with direct sales in local markets.
Watermelon is a relatively important specialty crop in Missouri with 3,100 acres valued at $8.4 million in 2017 (USDA-NASS, 2018: 2017 Agricultural statistics annual bulletin, Missouri), but down from over 5,000 acres in the mid-1990s and early 2000s (Roach et al., 2017: Historical perspective of the Missouri specialty crop industry. MU Extension). Furthermore, of the 352 watermelon farms, 12 farms manage 100 or more acres for a total of 2,111 acres, but 313 farms manage less than 5 acres for a total of 209 acres (USDA-NASS 2019: Census of agriculture, 2017 census by state-Missouri). Therefore, increasing watermelon production and recovering lost market share may not only revitalize and improve the economic sustainability of the industry, but also improve the wellbeing of small and medium-sized farmers.
This study funded by a Specialty Crop Block Grant (MDA-USDA-AMS) was conducted at the Horticulture and Agroforestry Research Center (HARC) in New Franklin, MO following a completely randomized block design with four replications for statistical purposes. We compared three production methods (figure 1): 1) growing watermelon under caterpillar high tunnels covered with greenhouse plastic film and in 2022, with low tunnel inside the high tunnel; 2) growing watermelon under low tunnels made of wire hoops and covered with spun-bonded row cover (1oz/sq-yd); and 3) uncovered open control. All transplanting were on black plastic mulch with drip irrigation. Fertilization and cultural practices followed standard recommendations. We used the watermelon cultivar Yellow Doll, an early (70-75 days to maturity) and small melon cultivar for early harvest. Transplants were grown in trays in the greenhouse (February-March) and had 2-4 true leaves at field planting. The goal was to plant in the tunnels the first week of April, but we delayed the planting in 2021 to April 23 to avoid freezing events that would have affected the uncovered open control. This planting postponement delayed harvesting time beyond the target Fourth of July market in 2021. Therefore, in 2022, we planted the high and low tunnels the second week of April to subject them to freeze events and evaluate the level of protection. The low tunnel inside the high tunnel provided an extra layer of protection. The uncovered open control was planted the last week of April after the freezes had passed. We also followed a couple on-farm low and high tunnels watermelon production operations that farmers were practicing with other "icebox" varieties (one was Sugar Baby, 75-80 days to maturity).
Figure 1 Watermelon production trial under caterpillar high tunnel (top left), low tunnel covered with spunbonded row cover (top right), and uncovered open control (bottom front). Horticulture and Agroforestry Research Center, University of Missouri-CAFNR.
Opening and closing tunnels depended on type and weather conditions. High tunnels stayed closed during cold weather and freezing events, and open with relatively warm weather. Temperatures inside the high tunnels were hot when closed and maximum temperatures in several sunny days reached over 125°F. Temperatures were warmest at night with over 38°F during freezing events (28°F). High tunnels stayed open during and after pollination of female flowers by bees. In general, male flowers appear first and after a couple weeks female flowers develop. If there are no beehives near the tunnels, then, bumble beehives can be set inside to assure pollination. Row cover in low tunnels stayed on continuously for 3-4 weeks until female flowers started to appear and then removed permanently for pollination since no freezing event was in the forecast. Like the high tunnels, temperatures were hot inside the low tunnel reaching maximum temperatures over 120°F in sunny days, but not as warm during cold nights. Temperatures were only 1°F to 3°F warmer inside the low tunnel than outside during freezing nights. Temperature differences vary with the thickness of the row cover material and weather conditions (wind, relative humidity, rain/snow, etc.). Two to three layers of row covers or thicknesses of 2-3 oz/sqyd can increase protection during freezing events. Removing the extra layers in warm days is necessary to avoid excessive shading. Differences in temperature among the three production methods influenced plant growth at the time of row cover removal from the low tunnels as shown in figure 2. The largest plants were under the high tunnels, then under the low tunnels, and the smallest in the uncovered control.
Figure 2 Differences in plant growth due to differences in microenvironmental conditions (temperature, wind solar radiation, and relative humidity) among treatments: high tunnel (top back), low tunnel (top right), and uncovered open control (bottom left).
We were able to start harvesting watermelons 1 to 2 weeks before the target Fourth of July market in 2022 only because of the early planting (figure 3). In 2021, harvest started the week after the target market for high tunnel watermelons and 2 weeks after for the other methods (data not shown). Similarly, growers monitored for their production of "icebox" watermelons under low or high tunnels started the harvest at least 1 week prior to the target market in 2022 (figure 4). In our study, the first harvest in 2022 was 2 weeks prior to the target market from the high tunnels with 8% of the total marketable melons. Then, we harvested an additional 21% of the marketable melons from the high tunnels and 15% of the marketable melons from the low tunnels 1 week before the target market. The rest was harvested after the target market. Harvest from the uncovered control in 2022 was lost due to activity of raccoons during the hot dry summer. In addition, watermelons grown under high tunnels had the largest yield both years. Also, yield of watermelons grown under low tunnel was larger than the uncovered control in 2021. Therefore, protected production systems have also the potential to increase yield.
Figure 3 Proportion of marketable watermelons harvested from high tunnels (HT) and low tunnels (LT) treatments prior to the target Fourth of July market in 2022.
Figure 4 "Icebox" type watermelon grown in a fixed high tunnel near Nevada, MO in 2022. Harvest started more than a week prior to the target Fourth of July market.
In summary, it is possible and there is potential to produce watermelons under protected production systems for the Fourth of July market in Missouri. To accomplish this, it is necessary to use early varieties (70 to 80 days to maturity), plant in early April with transplants grown in greenhouses, and make sure to manage the systems properly to protect against cold/freezing temperatures as well as ensuring good pollination.