If following the advice not to harvest forest stands within 10 years after the stands have been fertilized, this may mean that stands that have been fertilized between the first and second thinning have time to grow out of the second thinning window. The purpose of the study was to investigate the duration of the growth effect for forest fertilization in thinned pine stands in southern Norrland. For the study, 20 thinned pine stands with two different site indices (SI), T22 and T28, were used. After fertilization, the highest annual ring growth was reached for both SI already after 2 years. Stands that had been fertilized had at most 58 % higher annual ring growth than the stands that had not been fertilized. Between the two SI, there were no significant differences in a comparison between the fertilized stands from the year of fertilization and 12 years after fertilization. Already 9 years after fertilization, the growth is smaller than it was before any measures had been taken. Which shows that the stands can be thinned earlier than 10 years without losing growth effect.