The implementation of flower strips in agroecosystems is an effective measure to counteract the loss of biodiversity and enhance ecosystem services. Although beneficial effects for their main target group, flower-visiting insects, are assumed to be mediated by plant species composition and its associated floral characteristics, such as species richness and floral trait diversity, comprehensive studies investigating the establishment success and maintenance of different flower strip mixtures over time are rare. Therefore, we studied the performance of four different flower strip mixtures (two annual and two perennial) regarding their potential benefits in supporting flower visitors by evaluating spatio-temporal dynamics of plant community composition and six insect-relevant floral characteristics in a field experiment at three distinct study sites over three consecutive years. Moreover, we examined the impact of weed invasion on flower strips and how realized mixture performance under field conditions deviates from expected mixture performance. We found that both perennial flower strip mixtures undergo a significant community shift due to compositional changes in sown plant species after the year of sowing, strongly affecting mixture performance over time. The mixture with the highest initially sown species richness (51) outperformed all other mixtures after the year of sowing, regarding taxonomic (species richness and Shannon diversity) as well as functional floral characteristics (functional diversity and redundancy). Furthermore, deviation from expected mixture performance in both annual mixtures was largely explained by weed invasion, whereas in perennial mixtures, deviation was mainly caused by community changes in sown plant species (e.g. disproportional dominance of single species). We argue that perennial mixtures with a high number of native plant species provide a greater quantity of floral resources with more diverse niches for flower-visiting insects, with a greater resilience and temporal persistence than annual and less diverse mixtures.