PROBLEM TO BE SOLVED: To easily grasp the conditions of plants in the soil.SOLUTION: In a plant growth support system 100, a moisture content measurement device 1 measures, in the soil where plants are planted, the moisture content of the soil upper part and the moisture content of the soil lower part. An information terminal 2 determines the conditions of plants on the basis of values of the moisture content of the soil upper part and the moisture content of the soil lower part measured by the moisture content measurement device 1 and outputs the determination results.