Grafting is an alternative approach to reduce crop damage resulting from soil-borne pathogens and increase plant abiotic stress tolerance, which in turn increases crop production. There is usually consensus among researchers that grafting watermelons improve most of the vegetative growth and yield characteristics. On the other hand, there are still some differences in the literature as to the effects of grafting on some growth characteristics such as flowering and fruit ripening date. Two growing cycles per year, i.e. for early growing season (EGS) and late growing season (LGS) production, both of which are widely preferred in temperate climates have been investigated for their effects on plant growth and yield parameters such as main stem length, shoot dry weight, root length, number of days male and female flower formation, fruit ripening date and yield attributes. Two watermelon (Citrullus lanatus (Thunb.) Matsum and Nakai) cultivars (cv. 'Anthem F-1' and cv. 'Crimstar F-1') were used as the scion. Two C. maxima x C. moschata hybrids (cv. 'Shintoza F90' cv. 'Obez'), and one Lagenaria siceraria rootstock cv. 'Macis' were used as rootstocks. Self-rooted and self-grafted plants were used as control. EGS resulted in a reduction of main stem length, number of lateral stems, number of leaves, shoot dry weight and root length. On the other hand, number of days first male and female flower formation and number of days first ripe fruit increased comparing to LGS in both cultivars. However, some interactions between the growing season and the used cultivar also seem to exist. EGS reduced root dry weight of cv. 'Crimstar' but increased fruit number and fruit yield per plant of cv. 'Anthem'. Some of the plant growth and yield attributes increased when a specific rootstock-scion combination and growing cycle used. Neither the vigorous hybrids of C. maxima x C. moschata (represented by 'Shintoza' and 'Obez') nor Lagenaria siceraria represented by 'Macis' could be categorized as having constantly superior plant growth and yield traits for at least one of the cultivars in at least one of the field trials. It is important to evaluate and select suitable rootstock scion for each growing condition created by ecology and growing cycle, to guaranty high vegetative growth and yield.