Among the many benefits provided by plants, “health” stands out as a benefit that is especially highly valued. Over the past decades, people-plant studies have increasingly focused on empirically demonstrating relationships between plants and health. However, there are as yet no consensual standards in the field as to which research findings qualify as evidence for health benefits of plants. In this paper, we first argue that only studies that directly relate exposure to plants and green spaces to health outcomes should be admitted into the evidence base. We then discuss several studies that meet this requirement. An important conclusion is that the experimental evidence base for health benefits of plants seems to be less strong than the evidence provided by observational population studies linking green spaces to public health. Consequently, observational studies deserve more attention from horticultural professionals and other audiences who share an interest in health benefits of plants. However, as living in green areas is often accompanied by certain conditions and lifestyles that promote health, there is still an urgent need for more rigorous studies that allow for a causal interpretation of health effects of plants and green spaces.