The effects of root zone volume on the growth of snapdragon under optimum nutrient and water supply in soil culture or continuous flowing hydroponic system (CFHS) were investigated for seven weeks. In soil culture, seeds were sown in 30, 100, 300, and 1000 ml containers and fertigated with a 3/8 strength Enshi-shoho nutrient solution at 6-10 kPa (pFl.7-2.0) of soil moisture tension. In CFHS, plants were set on one reservoir and the volume of each plant was limited to 10, 30, 100, 300, and 1000 ml using cylindrical containers. A 1/8 strength Enshi-shoho nutrient solution flowed continuously at 170 ml / minute into the containers of CFHS for each plant. In soil culture, shoot dry weight at harvest significantly increased with increasing root zone volume. Leaf area and stem length of plants grown in 30 ml containers were smaller than that of others at three weeks after sowing. In CFHS, shoot dry weights of plants grown in 10 and 30 ml containers at harvest were lower than those of others in large containers grown on CFHS. Stem length, node number and leaf area were unaffected by root zone volume. In soil culture, reduced shoot growth was observed at a very young stage when the roots made contact with the container walls, but not on CFHS. These results indicate that the difference in growth of plants in soil culture was caused mainly by some substances retarding growth, probably originating from the roots rather than nutrient or water supply.