The basic shoot characteristics of ‘Karina’ and ‘Sylvia’ sweet cherry (Prunus avium L.) trees grafted on Gisela 3, Gisela 5, Piku 4, Weiroot 72 and F12/1 rootstocks were examined 3 years after planting. In both cultivars, F12/1 achieved a greater shoot length (SL) and diameter (SD) and a lower number of flower clusters per cm SL (NFC·cm−1 SL) than the other rootstocks. Furthermore, although the two cultivars had different growth vigour, they exhibited similar differences in SL, SD and NFC·cm−1 SL among the rootstocks. The correlation between SL and NFC·cm−1 SL was 34.4% and 39.9% greater than the correlation between SD and NFC·cm−1 SL in ‘Karina’ and ‘Sylvia’, respectively. Regression analysis for both cultivars on particular rootstocks and for the mean values across the rootstocks showed that there was a logarithmic relationship between SL and NFC·cm−1 SL, with r2 values of 0.703 and 0.694 for ‘Karina’ and ‘Sylvia’, respectively, when the responses were fitted by logarithmic function models. The minimum and maximum NFC·cm−1 SL predicted by these models were approximately 0.01 and 0.9 (for SL = 145 and 7 cm, respectively) for ‘Karina’ and 0.0 and 0.9 (for SL = 150 and 5 cm, respectively) for ‘Sylvia’. These findings combined with data obtained in previous studies suggest that NFC·cm−1 SL can be used as an index for predicting the fruiting potential of young sweet cherry trees.