Coding and description of phenological stages of blue honeysuckle (Lonicera caerulea L.) according to the BBCH scale

• The first documentation of blue honeysuckle phenology is provided. • Annual growth was characterized by eight primary and 35 secondary growth stages. • Overlapping flowering times indicate cultivars can serve as mutual pollinizers. • Extent of sepal withering may serve as an indicator for assessing fruit maturity. Blue honeysuckle ( Lonicera caerulea L.) is an emerging fruit crop from the temperate to circumpolar climate regions with outstanding agronomic traits, substantial nutritional value, and versatile processing applications. However, the limited understanding of its phenology poses substantial challenges to its cultivation, breeding, and research. In this study, we characterized the progressive phenological growth stages of blue honeysuckle according to the BBCH (Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie) scale by investigating three major cultivars ( L. caerulea ) and a wild accession ( L. caerulea var. edulis ) in Harbin, China (hot-summer humid continental climate) during 2022–2023. The annual growth of blue honeysuckle was characterized by eight primary stages, including bud development (0), leaf development (1), shoot development (3), inflorescence emergence (5), flowering (6), fruit development (7), fruit ripening (8), and senescence and dormancy (9). Additionally, 35 secondary growth stages were documented, among which eight stages are related to fruit development and ripening. The annual growth period of blue honeysuckle spans 6.5–7 months, starting from late March and ending in early October. The flowering season lasts for 2–3 weeks, ranging from late April to mid-May. The fruit development and ripening last for 7–9 weeks, beginning in early May and ending in early July. This study provides valuable insights for the cultivation and research of blue honeysuckle.