A conceptual model was developed, describing the short-term, medium and long-term effects of plants on the indoor climate and the health and well-being of people. The model was tested by means of intervention research at three companies and eight homes for the elderly. The effect of plants on the physical indoor climate was measured with sensors, the effect on the health and well-being of employees with questionnaires. In principle, a ‘Before After Control Impact’ approach was used at the locations. A control room and an intervention room were selected for each location. After a pre-measurement, plants were placed in the intervention room and up to three post-measurements were conducted. At the companies, significant effects were found on relative humidity (up), attractiveness of the workplace (more attractive), state of mind (more positive), satisfaction with own functioning (higher) and sickness absence reporting (less). The need for recovery after a working day showed a reversed effect (rising). No significant effects were found for the other variables in the model. Similar effects were not observed in the homes for the elderly. Possible reasons for the latter are: the small number of employees working in the same room (i.e., living room for clients), a low willingness amongst these employees to participate in the study (high work pressure), a high mobility amongst employees and working in both the intervention and the control room.