To reduce cost of raising young plants obtained from a runner of strawberry or the like by using a carbonized material obtained by carbonizing bark of Japanese cedar or the like as a culture medium.

Bark culture medium 3 which is obtained by fermenting and carbonizing bark in a temperature range of 35 to 45°C for 2 to 8 months, desirably for 7 to 8 months, is filled into a substantially cylindrical container made of a water soluble or biodegradable material to form a molded body 2 of the bark culture medium, and the molded bodies are arranged around a parent plant 6 of strawberry. A runner 4 extended from the parent plant 6 is fixed on a surface of the bark culture medium 3. After roots generated from the runner 4 are grown into a new plant, it is permanently planted into separately prepared culture medium for permanent planting, together with the molded body 2 of the bark culture medium.