Abstract: Peat moss having water repellency when it is dry is used as culture soil by subjecting it to a water repellency preventing treatment. In addition, a seedling-growing peat board with few germs and impurities, being lightweight and easy to handle, and particularly suitable for use as bed soil of a seed bed, is provided. The culture soil contains peat moss which is water repellent when dry, and a water-absorbing clay adhered to the surface of the peat moss. This is accomplished by treating water to render it absorbable by peat moss, suspending a water-absorbing clay in the treated water, contacting the peat moss with the suspension to absorb the suspension onto the surface of the peat moss, and drying the peat moss.