Organic competence of different explant sizes and locations on watermelon seedlings was determined by calculating the percentage of cotyledon explants that produced adventitious shoots. About 52% (214/412) of explants prepared from the proximal region of cotyledons formed shoots, whereas only ≈6% (24/411) of distal explants did so. Shoot formation was limited to the proximal end of basal explants but was not restricted to any specific region on distal ones. The percentage of explants that produced harvestable shoots was greater from basal halves than basal quarters in `Sweet Gem', `Crimson Sweet', and `Minilee', but explant size did not affect adventitious shoot regeneration of `Yellow Doll', resulting in significant interaction between cultivar and explant size. This study indicates that cultivars that respond poorly to in vitro procedures may have fewer cells competent for shoot regeneration, requiring special care during explant preparation.