Objective  Morphology and endogenous hormones of Bombax ceiba flower buds in differentiation were studied to aid the control of fallen debris at fruiting stage of the popular landscape plant in southern China.

  Methods   Morphology of the flower buds of B. ceiba at differentiation phases were observed with the paraffin sections under a microscope and contents of endogenous GA₃, IAA, ABA, and ZR determined.

  Results  The flower bud development was classified in the phases of pre-differentiation, primordium differentiation, sepal primordium differentiation, petal primordium differentiation, stamen and pistil primordium differentiation, and stamen and pistil formation. The flower primordium differentiated in early October, while the sepal primordium did in mid-October, the petal primordium in late October, the female and stamen primordium in mid-early November, and the female and stamen formed in late November. During differentiation, GA₃ and ABA in the buds were significantly higher than IAA and ZR. They generally decreased, but IAA declined at first, followed by an increase and another decline, whereas ZR rose initially and fell subsequently. The ratios of ZR/GA₃ and (ZR+IAA)/GA₃ were on an increasing trend, GA₃/IAA decreasing, ZR/IAA and ABA/IAA rising at first followed by declining, ABA/GA₃ rising-falling-rising, and (GA₃+ZR+IAA)/ABA falling-rising-falling as the differentiation progressed.

  Conclusion  The process of B. ceiba bud differentiation can be divided into six stages based on its morphological structure, in which the contents of ABA and GA₃ are much higher than those of ZR and IAA , and the changes in the contents showed a significant negative correlation with the bud differentiation process. Consequently, applying either GA₃ on the plant prior to the process begins or ABA at the petal primordial differentiation phase could deter the floral development and mitigate the nuisance of causing human allergy and traffic interference due to the massive tree falloffs.