Most angiosperm species complete fertilization within 24 to 48 h after pollination. However, a delay in fertilization of more than several days or months has been reported in several lineages of angiosperm. The family Fagaceae, the most diverse tree family in northern temperate regions, including oaks and beeches, contains an exceptional number of species with delayed fertilization. Although the phenomenon has been recognized for a long time, the underlying mechanism and its adaptive significance remain largely unknown. To investigate the mechanism of delayed fertilization, we observed seasonal progression of pollen tube growth and ovule development in Lithocarpus edulis, which blooms both in spring and autumn. In. L. edulis, pollen tubes reached the style-joining site within 2 months after pollination and stopped elongation before winter regardless of spring or autumn flowering samples. In both spring and autumn flowering samples, some pollen tubes resumed growth in May of the following year of flowering and reached the embryo sac in June for fertilization. The seasonal progression of ovule development was also consistent between spring or autumn flowering samples: differentiation of ovule primordia was initiated from February to April of the following year of flowering, which was followed by embryo sac development in May and maturation in June. These results indicate that pollen tube growth is arrested, and ovule development is delayed during winter regardless of flowering time. This finding suggests that delayed fertilization serves as an adaptive strategy to achieve fertilization in spring, overcoming the cold winter season that is unstable for reproduction.