The ”Kongo-sakura„ at the Nikko-san Rinno-ji Temple, which has been designated an important cultural property of Japan, had started to lose its vigor from around 1990. The Nikko City Council for the Protection of Cultural Properties gave directive for removal of the decayed parts of the trunk and antiseptic treatment. A project to recover the vigor of the tree was started. Since decay of the trunk had advanced to such a state that removal of decay from the trunk was not possible, the project aimed to recover tree vigor by using the adventitious roots. Since several adventitious roots had reached the soil surface, the soil around these roots was improved and enriched with nutrients. From the results of soil analysis, a preparation containing fermented rice bran, bark compost, bone meal, and charcoal was used as soil improvement material, and perlite was used to improve water drainage. Furthermore, Green Pipes were installed to improve the insufficient oxygen due to treading on the soil. The soil improvement project was conducted over three years from 1998. The beneficial effect started to manifest from around five years after the project. The density of leaves increased, and the amount of elongation of the branches also increased that year, accompanied by a greater number of flowers. At the time of full bloom in May 2011, the number of flowers had recovered to the level at the prime time of the Kongo-sakura.