The list of Sustainable Development Goals created by the United Nations include good health and well-being as one of its primary objectives. Pollution is a concern worldwide, and pollution levels inside buildings (homes or workplaces) can be higher than outdoors. To alleviate this problem and improve air quality, ornamental plants can be used. This paper presents the application of Internet of Things (IoT) technologies to develop a system called P4L, an acronym for “Plants for Life”. The objective of P4L is the automated care of potted plants to improve air quality and make the indoor environments of a building healthier. This IoT-based system (IoTS) has been developed through low-cost Arduino-compatible components. In addition, the Test-Driven Development Methodology for IoT-based Systems (TDDM4IoTS) has been used to guide P4L development. In fact, this article shows the result of the application of this methodology (phase by phase), with the help of the Test-Driven Development Tool for IoT-based Systems (TDDT4IoTS), which supports the aforementioned methodology, to develop P4L. To validate the methodology, we conducted a survey among developers that have used it, the results of which show that it is efficient and covers all aspects of IoTS development.