The dissertation presents a theoretical generalization and a new approach to solving the scientific problem of optimizing elements of technology for growing grafted watermelon hybrids in the conditions of the Left Bank Forest Steppe of Ukraine. The technology is based on the study of the following factors: the selection of combinations of rootstocks for growing diploid hybrid Yukon F1 watermelon and triploid Kidman F1 watermelon with different plant densities, taking into account the characteristics of hybrid rootstocks. A summary of achievements and analysis of scientific research by domestic and foreign authors regarding the growth and development features of grafted diploid and triploid watermelons was carried out. The urgency of introducing the use of rootstocks for watermelons in the open field into production has been determined. For the first time, the peculiarities of the formation of the grafted watermelon crop were experimentally investigated and substantiated. Biological features of grafted watermelons were studied. Grafted watermelon plants had the longest length of the main stem, in the phase of the beginning of fruiting, compared to ungrafted ones. Thus, on a watermelon of the Yukon F1 hybrid grafted on the Cobalt F1 rootstock, it was 358 cm, which is 28,3 % more than on the control, and on the Pelops F1 rootstock by 24,7 %. The largest leaf surface area over the years of research was on Yukon F1 watermelon plants grafted on Cobalt F1 rootstock, which averaged 3.40 m2, which is 74,4 % more than ungrafted plants, and on Pelops F1 hybrid rootstock 62,1 % more than on ungrafted plants. The analysis of the results of the yield of watermelon indicates a significant advantage of grafted plants over non-grafted ones. Over the years of research, the Yukon F1 watermelon grafted on the Cobalt F1 rootstock had an average yield of 79,0 t/ha. When studying the influence of the density of grafted plants on productivity, it was established that the highest yield of the grafted diploid hybrid watermelon Yukon F1 on the rootstock Cobalt F1 was obtained on plants with a density of 4 thousand/ha, which was 82,9 t/ha, which is 3,6 t/ha more than at a density of 3 thousand/ha, and by 10,4 t/ha more than at a density of 5 thousand/ha. Cultivation of grafted watermelon hybrids Yukon F1 and Kidman F1 on Pelops F1 and Cobalt F1 rootstocks is economically beneficial. The largest yield of the Yukon F1 hybrid – 79,0 t/ha and a net profit of UAH 111,295/ha was obtained when using the Cobalt F1 rootstock.
