PROBLEM TO BE SOLVED: To provide a soil conditioner having excellent plant growth-promoting performances, a soil-conditioning method for bringing the soil into a state suitable for cultivation of a plant, and a method for cultivating a sound plant. SOLUTION: The soil conditioner comprises a substrate comprising cellulose extracted from an oil-producing plant and a living bacterium carried on the substrate. The soil-conditioning method comprises bringing the soil to which the above soil conditioner has been applied into a wet state. The method for cultivating a plant comprises cultivating a plant in the soil to which the above soil conditioner has been applied.
