Abstract: Seedlings of three tomato cultivars, 'Reika', 'Marryroad' and 'First Power' were grown in either pots or plug trays in order to clarify the interaction effect of cultivar and root container size on the number of days to flowering and the number of leaves preceding the first inflorescence under different temperature regimens. The number of days to flowering was greater in seedlings raised in plug trays than those in pots, regardless of temperature regimen. Flowering was delayed at 23/18?C compared with 30/25?C for seedlings raised in either pots or plug trays. The number of leaves preceding the first inflorescence was greater in seedlings raised in plug trays than those in pots, except for 'Marryroad' at 23/18?C. Regardless of root container size, the number of leaves preceding the first inflorescence was greater in 'First Power' than in 'Reika' and 'Marryroad' at 30/25?C. These results suggest the importance of cultivar choice for the production of tomato seedlings with a small number of leaves preceding the first inflorescence using plug trays in cool conditions.