PROBLEM TO BE SOLVED: To provide a sterilizing method by which the efficiency of planting soil-preparing works can be improved, and to provide a sterilizing stirrer with which all preparing works including a sterilizing work can be carried out. SOLUTION: This method for sterilizing the planting soil is characterized by charging a planting soil base material 7 into a receiving tank 2 having a stirring means comprising a horizontal shaft 3 and blades 4 attached to the shaft, stirring the planting soil base material 7 with the blades 4 of the stirrer, and jetting steam 53 from jetting ports 32 disposed in the horizontal shaft 3 of the stirrer, thereby simultaneously stirring and sterilizing the planting soil base material 7. The sterilizing stirrer 1 is formed by disposing the receiving tank 2 having at least a port 23 for charging the planting soil base material 7, and also disposing the stirring means comprising the horizontal shaft 3 and the blades 4 attached to the shaft, in order to stir the planting soil base material 7 in the receiving tank 2. A path 33 for conducting the steam 53 is formed in the horizontal shaft 3 of the stirring means, and ports 32 for jetting the steam 53 are disposed on the periphery of the horizontal shaft 3.
