Typically, hydrangea (Hydrangea spp.) plants produce flowers from early to mid-summer. However, their basal shoots often continue to produce flowers from late summer to autumn, and we call this unseasonal flowering. The flowering frequencies and flowering period durations of basal shoots were studied using 23 hydrangea cultivars and lines in 2017, 2018, and 2019. The flowering frequencies of basal shoots were relatively high in ‘Christmas’, ‘Endless Summer’, ‘Ezo’, ‘Rosea’, and ‘Sumida-no-hanabi’ in each year of the study. The flowering period durations of basal shoots ranged from one to six months among the cultivars and lines studied. Basal shoots of ‘Endless Summer’ and ‘Rosea’ continuously flowered during each year of the study period. The basal shoots of ‘Hatsushimo’, ‘Jyogasaki’, ‘Maihime’, ‘Masja’, ‘Ms. Hepburn’, ‘Uzu’, and No. 5 never flowered after August in any of the study years. Using ‘Masja’ and ‘Rosea’, axillary buds expected to develop into basal shoots were studied for flower bud initiation in November 2018. Flower bud initiation was observed in 8.9% and 77.4% of axillary buds of ‘Masja’ and ‘Rosea’, respectively. The number of nodes produced before flower bud initiation in the buds ranged from 10 to 12 and 8 to 13 in ‘Masja’ and ‘Rosea’, respectively. The numbers of nodes corresponded to those of the basal shoots that flowered up to August 2019 in both cultivars. The number of nodes produced by basal shoots of ‘Rosea’ that flowered after August 2019 ranged from 14 to 19, which was higher than those observed for the axillary buds expected to develop into basal shoots in November 2018. In conclusion, the flowering period duration of hydrangea basal shoots differs among cultivars. The floral initiations on the apical buds of the basal shoots after the previous autumn largely contribute to unseasonal flowering occurrences after August in hydrangea.

通常，绣球（绣球spp。）植物从夏初至夏开花。然而，从夏末到秋季，它们的基生芽经常继续开花，我们称其为非季节性开花。在2017年，2018年和2019年使用23个绣球品种和品系研究了基部芽的开花频率和开花期持续时间。在“圣诞节”，“无尽的夏天”，“ Ezo”，“该研究的每年都有Rosea和'Sumida-no-hanabi'。在所研究的品种和品系中，基部芽的开花期持续时间为1-6个月。在研究期间的每年中，“无尽的夏天”和“罗西亚”的基础芽不断开花。'Hatsushimo'，'Jyogasaki'，'Maihime'，'Masja'，'Ms。Ms. Hepburn”，“ Uzu”和No. 在任何学习年的8月之后，没有5花从没开花。使用“ Masja”和“ Rosea”，研究了预计会发展成基础芽的腋芽，用于在2018年11月进行花芽萌芽。“ Masja”和“ Rosea”的腋芽中有8.9％和77.4％观察到花芽萌芽，分别。在“ Masja”和“ Rosea”中，花蕾萌芽前产生的节数分别为10至12和8至13。两个品种的节节数量与截至2019年8月的基芽的节数相对应。在2019年8月之后开花的'Rosea'基芽产生的节数范围为14到19，这高于观察到的预计在2018年11月发展为基芽的腋芽的结节数。总之，绣球基部芽的开花期持续时间因品种而异。去年秋天之后，基部芽的顶芽上的花期萌生在很大程度上导致了八月后绣球的非季节性开花。