In this article, we identify possibilities and limits of processing as yet unused data sources for spatio-temporal biodiversity trend analyses in Germany. The sMon synthesis project (https://www.idiv.de/smon) of the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig is a joint working group of federal and state authorities cooperating with natural history societies, nature protection organisations and scientific institutions. In this group, we develop and evaluate methods for using heterogeneous data for retrospective trend analyses over the last decades. Building on this, we propose viable approaches for the future of German biodiversity monitoring and illustrate how data from the past can help to shape monitoring in the future.