To reveal temporal variability of archaeal and bacterial abundance, community structure, as well as microbial biomass and activity, soils of different ages (young, intermediate, mature) were sampled along a glacier foreland in the Austrian Central Alps, at the beginning (summer) and at the end (autumn) of the plant growing season. No significant changes of 16S rRNA gene copy numbers of bacteria or archaea occurred in the young, recently de-glaciated soil. However, in intermediate and mature soils, bacteria were more abundant in autumn than in summer, whereas archaea decreased at the end of the growing season. Bacterial and archaeal community structures were differentially affected by the sampling date. Both soil microbial biomass and microbial activities in intermediate and mature soils significantly increased in autumn. On the contrary, the overall abiotic parameters did not undergo changes during summer. Bacterial communities at young, intermediate, and mature sites formed different clusters, thus reflecting changes according to soil age. Archaeal communities, on the other hand, were mainly influenced by the growing season, at least in young and intermediate soils. Our results indicate that temporal variations of microbial activities, biomass, and abundance in alpine glacier foreland soils distinctly increased along with the age of the soils and highlight the importance of sampling date for ecological studies.