Citizen science has gained importance in recent years and revealed great potential, especially regarding science learning and environmental education. However, little is known about ways of supporting individual learning processes within citizen science. With this in mind, a home experiment set, the Nitrogen Box, was developed within a chemistry citizen science project on nitrogen pollution of water bodies. The aim of the box was primarily to deepen the subject matter and to sensitize the citizens to the topic. To gain deeper insights into the usability and added value of home experiments in a citizen science context, semi-structured interviews were conducted with ten citizens. Analysis of these interviews revealed that the nitrogen box contributed to a consolidation and deepening of knowledge of the nitrogen problem in Northwest Germany. Home experiment sets like Nitrogen Box can motivate and enable citizens to engage more deeply with the scientific topic in the future, to reflect on it and discuss it. We discuss how heterogeneity of the target group presents challenges for designing citizen science projects and provide recommendations for the future projects.