Water spinach (Ipomoea aquatica) is leafy green vegetable that is routinely cultivated in Southeast Asia. Due to its aggressive growing habit and potential to become established in waterways, it has been classified as a federal noxious weed within the United States. However, recently, ethnic communities in the Atlanta, Georgia, USA metropolitan region have expressed an interest in being able to cultivate water spinach for local sale. The objective of this study was to develop recommendations for the establishment of growing degree day (GDD) estimates and yields for harvest for three planting periods for organic cultivation of two selections of water spinach in a high tunnel environment during the summer months in Watkinsville, Georgia USA. Selection 1 had a hastate leaf shape, while selection 2 had a more lanceolate leaf shape. Plantings were conducted on three dates (May, June, July) during summer 2023. Plots contained 36 plants and were arranged factorial randomized complete block design with four replicates with selection and planting date being the main effects. Once plants reached a marketable harvest size, the above-ground portions were cut near the plant base, which repeated during the growing season. Our results indicated that planting water spinach in May resulted in significantly greater yields compared to June and July plantings due to a greater number of harvests and biomass production at each harvest. Using a sweetpotato (Ipomea batatas) growth model, the GDD at harvest for the May planted water spinach were 390, 271, and 301 for the 7 Jul, 1 Aug and 26 Aug harvest periods, respectively. The rate of fresh weight biomass production for these harvests ranged from 41,469 kg ha-1 to 49,398 kg ha-1 for selection 1 and 24,266 kg ha-1 to 45,432 kg ha-1 for selection 2. Total Fresh weight biomass for all three harvests (7 Jul through 26 Aug) for the May plantings were 136,800-1 and 102,300 kg ha-1 for selections 1 and 2 respectively. July plantings had a greater GDD accumulation at harvest, but yields were significantly lower than earlier plantings. Our results suggest that water spinach could be successfully grown in high tunnels in Georgia, USA during the summer months. Further, while some plants did produce flowers, the chance for off-site movement of seeds and plant material was minimal as plants were confined to a high tunnel structure.
