A wilder garden may support residents’ immune systems, Finnish study finds

A Finnish study reported by Yle found that making home gardens more biodiverse was linked to changes in residents’ skin and mouth microbiomes within three months. The researchers say the findings support leaving some leaves to decompose and converting parts of lawns into meadows, though longer-term health effects need further study.

Researchers added varied vegetation, deadwood, wood chips, microbe-rich growing medium and leaf composters to some gardens. Residents were asked to leave autumn leaves on the ground rather than rake them and to allow parts of their lawns to grow into meadows. Residents of comparison gardens continued their usual gardening practices.

Residents of 36 detached-house gardens provided samples over three months. The study was conducted by Tampere University, Benefa Oy and the Natural Resources Institute Finland, and published in the journal Microbiome.

Microbiome changes appeared within three months

The researchers found that skin microbiome diversity persisted further into autumn among residents of the gardens made more natural. Bacteria associated with natural environments increased, while the relative abundance of bacteria associated with infections decreased.

Changes were also found in the composition and functional properties of the mouth microbiome, including in metabolic pathways. Greater diversity in the mouth microbiome was associated with a lower level of the inflammation marker IL-6 in saliva.

“Our interpretation is that this has beneficial effects at the level of the immune system,” said Olli Laitinen of Tampere University, who led the biochemical and immunological analyses.

The groups spent similar amounts of time in their gardens, suggesting that the type of garden environment, and not only time spent outdoors, may matter. The researchers said contact with soil and plants, such as when gathering produce, provides more exposure to nature than simply breathing in the garden.

Deadwood linked to natural-environment microbes

The amount of deadwood in participants’ surroundings was linked to the presence of more microbes associated with natural environments in their skin and mouth microbiomes. Lead author Marja Roslund of the Natural Resources Institute Finland said the study also found changes in the microbiomes’ metabolic pathways.

One participant, Kaspar Abella, said his garden now has more plants and raised growing beds, while the lawn has been reduced by about half. The changes had not greatly affected how the garden was used, he said.

The researchers described the study as the first to show that making home gardens more natural affects people’s microbiomes and inflammatory responses. They said further research is needed to establish the long-term health effects.