This longitudinal study explored the roles of item- and learner-related variables in L2 learners' development of productive collocation knowledge (L1 = Dutch; L2 = German; NLearners= 50). Learners' form recall knowledge of 35 target collocations was measured three times over a 3-year period. The item-related variables investigated were L1-L2 congruency, corpus frequency, association strength, and imageability. We also explored the learner-related variables L2 prior productive vocabulary knowledge and L2 immersion. Mixed-effects regression modeling indicated a significant effect of time, congruency, and prior productive vocabulary knowledge on learners' collocation learning. While learners' knowledge of congruent collocations remained relatively stable after year one, knowledge of incongruent collocations increased significantly. Learners' prior productive vocabulary knowledge was clearly associated with growth of productive collocation knowledge, but besides overall growth there were instances of attrition.