Applied Research and Cooperative Extension Programs Support Adoption of Grafted Watermelons in California
Search for Excellence in Crop Production
Zheng Wang
Vegetable Crops Farm Advisor
University of California Cooperative Extension
Modesto
Team Members:
Wang, Z*1, Castrejon, Y2
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Vegetable Crops Farm Advisor, University of California Cooperative Extension, Modesto, California, 95358
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Specialist, University of California Cooperative Extension, Modesto, California, 95358
Abstract
Research on vegetable grafting in California primarily began in 2016 focusing on improving rootstock performance for yield and quality of processing tomatoes. To combat high costs for rootstock seeds and seedlings, tremendous tomato rootstocks were tested on commercial fields under regular and reduced populations. However, inconsistent yield and quality performance as well as labor challenges did not show horticultural and economic advantages over conventional production, thereby discouraging researchers from further tests. While passion and interest in grafted processing tomatoes eroded, a growth of attention to grafted watermelons initiated in 2019 in California’s San Joaquin Valley. Currently, grafted watermelon acreage in California reached 2,500 by the 2024 season, which was 15 times more than the acreage in 2019. Reasons for such rapid adoption are multi-facet. First, compared to processing tomatoes, watermelon fields use much less plants/acre, bringing a lower cost for grafted transplants. Second, watermelon rootstock seeds cost less than tomato rootstocks. Third, watermelon is a high value crop compared to processing tomatoes. These advantages deliver a clear pathway to profitability for growing grafted watermelons. Since 2019, University of California Cooperative Extension Vegetable Production Team in Stanislaus County has built holistic watermelon grafting research and extension programs from providing resources for obtaining grafted seedlings to science-based information on performances of different rootstock-scion combinations to meet growers’ needs. By following our recommendations, growers benefit from reducing 40% of plants/acre while gaining 25% more yield on average than conventional production, which is equivalent to an increase of net income by $1,500/acre. In addition, growers use grafting as a tool to facilitate other agricultural practices on irrigation, nutrient, and disease management. In 2026, the estimated acreage of grafted watermelons may increase to 3,000 (25% of statewide acreage). Moving forward, as more tomato rootstocks and mechanical grafting are being commercialized and adopted, production cost may drop tremendously, thereby re-stimulating passions for grafted processing tomatoes in California. The future trend also indicates that watermelon grafting should be used as a tool that is leveraged to meet growers’ needs and enhance their resilience.
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