Eulychnia acida Phil. is an arborescent cactus species endemic to Chile, and widespread in the Coquimbo Region, Chile. Wild populations are found on north facing slopes and vary morphologically in fruit shape and color. We conducted a study on reproductive phenology at three locations in the region: Quebrada Honda in the coastal area, Gualliguaica in the Elqui Valley, and La Coipa in the Limari Valley. A total of 120 stems from 30 selected plants of wild populations were monitored weekly and the phenological stages were evaluated over a season. Through multivariate analysis was determined if climatic factors affected the number of individual and/or reproductive organs observed. The presence of reproductive phenophases is asynchronous, beginning in late autumn with the appearance of flower buds, which bloom mainly in spring and set at the end of the season. Flowering has a unimodal pattern. The variable fruits by stems is strongly correlated (p < 0.05) with the relative humidity (negative) and the degree days (positive). Locations show differences in the duration of the phenological events, which appear to be related to plant size and abundance of reproductive structures. Flowering synchrony among individuals is low when compared with other cacti; this means less overlap of the flowering periods among individuals, which could be a strategy to ensure insect visitation and pollination. Longer term studies are necessary to establish how weather conditions, rainfall and temperature influence the generation of flower buds, since production is affected in periods of drought.