Stem segments from terminal leaders of Douglas‐fir, Pseudotsuga menziesii (Mirb.) Franco, seedlings were sampled in mid‐December when cambial cells were dormant. The residual, debudded leaders were resampled again in early May when the cambium was metabolically active. May stems had higher constitutive ethanol concentrations than December stems. This was not the result of cambial hypoxia generated by rapid spring respiration rates, because when aerobic respiration was stimulated by incubating the stems in air at 30 °C ethanol production was induced in December, but not in May. Rapid respiration rates at 30 °C may have depleted O2 supplies and induced ethanol production in December stems because dormant, thick‐walled cambial cells may be less permeable to CO2 and O2, compared with metabolically active, thin‐walled cambial cells in May. December stem segments incubated in a N2 atmosphere at 30 °C synthesized 1.8 times more ethanol than segments from May, most likely because spring growth had reduced the soluble sugars available for fermentation. CO2 efflux from May stems (after 5.5 h of incubation at 30 °C) was equal to December stems per unit volume, but greater than December stems per unit surface area. N2‐induced ethanol concentrations were positively related with CO2 efflux per unit volume, indicating that rapidly respiring leaders can maintain rapid fermentation rates, provided soluble sugars are readily available. N2‐induced ethanol and CO2 efflux per unit volume declined with increasing leader diameter in both seasons, whereas there were no relationships between CO2 efflux per unit surface area and diameter. Cambium physiology and phenology influence the induction of fermentation and concentrations of ethanol produced in terminal leaders of Douglas‐fir, and probably other conifers as well. This needs to be considered when comparing fermentation among species, or comparing individuals from different seasons, or disparate ages within a species.