“The glory of gardening: hands in the dirt, head in the sun, heart with nature. To nurture a garden is to feed not just the body, but the soul.” – Alfred Austin

Gardeners have been knowing for centuries that their hobby gives them joy and peace. In today’s fast-paced world, gardening has become a form of stress therapy for many. There is even an organization called the American Horticultural Therapy Association, which is “committed to promoting and developing the practice of horticultural therapy as a unique and dynamic human service modality.”

The first Saturday of May is World Naked Gardening Day, a growing annual tradition that represents the ultimate act of getting in touch with nature. Even if you remain clothed, there is a uniquely good feeling about interacting with plants and the soil.

As with so many things, science introduces us to the physical wonders behind what we already know on a subliminal level. There are two interesting pieces of research that give credence to the feeling that our bodies and souls are better off from gardening.

Researchers reported in the journal Neuroscience that contact with a harmless soil bacteria called Mycobacterium vaccae triggers the release of serotonin in the brain. This type of serotonin acts on several different pathways, including mood and learning. Lack of serotonin in the brains is related to depression.

“These studies help us understand how the body communicates with the brain and why a healthy immune system is important for maintaining mental health,” said lead author Dr. Chris Lowry. “They also leave us wondering if we shouldn’t all be spending more time playing in the dirt.”

Basically, the things we do as gardeners—working the soil, planting, mulching, and so forth—can really contribute to happiness. We ingest the bacteria by breathing or through broken skin. The simple act of children playing outside in the grass and dirt can be a natural way for them to reduce anxiety.

In addition to increasing happiness and reducing anxiety, serotonin has positive effects on memory and learning. Research presented at the American Society for Microbiology shows that feeding live M. vaccae bacteria to mice significantly improved their ability to navigate mazes, due to the fact that the bacteria triggers the release of brain serotonin.

“This research suggests that M. vaccae may play a role in anxiety and learning in mammals,” said researcher Dorothy Matthews. “It is interesting to speculate that creating learning environments in schools that include time in the outdoors where M. vaccaeis present may decrease anxiety and improve the ability to learn new tasks.”

Have you noticed that you feel really happy when picking those ripe vegetables, especially that first tomato of the season? It turns out that harvesting fruits and vegetables triggers the release of dopamine in the brain. The speculation is that this evolved over 200,000 years of humans harvesting food as hunter-gatherers. Dopamine is strongly correlated with reward-motivated behavior. So there we have it—two physical reasons why people can be happier and smarter through gardening. Being a gardener myself, I have several other hypotheses that may contribute to this body of research. These include, but are not limited to: the myriad of colors in plants and animals, trees swaying in the wind, birds singing, squirrels chattering, lady beetles, and fresh air. Perhaps one day we’ll have scientific explanations for all this, but in the meantime we can take comfort in that innate feeling we know is there.