We measured colony growth over a three year period in the obligate epiphytic moss Neckera pennata Hedw. in three forest sites in eastern Sweden. Increment in colony area was proportional to colony size; hence area growth was modelled with the exponential growth function. Growth was measured over four periods (ca 0.5 to 1 yr long), among these periods relative growth rate varied between 0 and 35% yr⁻¹ with an annual growth rate of 13.6% for the whole studied period. Colony growth was correlated with precipitation during the periods and this relationship was used to calculate relative growth rate at normal precipitation. The regressed relative growth rate (18.2% yr⁻¹) was utilized to model average colony growth over time, from establishment to a colony size of 250 cm². The model was also used to estimate age of first reproduction, which occurred at a colony size of 12–79 cm², corresponding to an estimated age of 19–29 yr. Precipitation was the most important variable explaining colony growth, but some other factors were also of significant importance. Cover of other epiphytes surrounding the colony had a clear negative impact on growth of the N. pennata colonies, which we interpret as interference competition. Our study suggests that N. pennata was forced up the stem by stronger competitors and that growth position up to 170 cm did not impair growth. However, neither the tree species, bark pH, soil moisture, nor forest site affected colony growth, suggesting that occurrence of N. pennata was restricted by establishment rather than by growth.