Phyllostachys praecox bamboo stands significantly recede after 3 or 4 years using an organic-material mulching technique consecutively. We hypothesized that the bamboo recession is caused by the up-floating of underground rhizome stimulated by soil hypoxia through the mulching technique. This study aimed to validate this hypothesis by field investigation. Bamboo underground rhizome distribution in the soil profile of P. praecox subjected to various mulching times was investigated. Results showed that bamboo rhizome weights and lengths increased with increased mulching time. However, after 4 years of mulching, the number of fresh rhizomes decreased significantly, and more than 50% of rhizomes floated upward to the shallow soil layer (0-10 cm). Moreover, the 0-10 cm soil layer suffered severe acidification that severely impeded bamboo-rhizome growth. The soil hypoxia induced by the mulching technique must be responsible for the bamboo rhizome up-floating. We confirmed that bamboo rhizome up-floating was the critical factor that caused the bamboo growth to recede under the mulching technique. Therefore, managing this bamboo rhizome up-floating is the key to sustainable bamboo production. The effect of soil hypoxia in the absence of flooding or waterlogging on plant root growth also warrants further and extensive study.