Mud, wild plants, moss. And then again foliage of all kinds, rain, small insects. Childhood should be spent like this, in the midst of nature that couldn’t be more nature. They have understood this well for years in Finland, where there are now dozens of nursery schools that have received funding to renaturalize gardens and increase children’s exposure to the microscopic biodiversity that lives in nature.
A project born from a growing body of research that connects two layers of biodiversity: the external one, which includes plants and animals, and the internal one, present in the human body, such as the intestine, skin and respiratory tract.
In The Guardian the story is beautiful and fascinating. Aurora is 5 years old and in her nursery she is preparing a very special cake: sand, mud, leaves, some “imaginary carrots” and a little water. “It’s burnt, we need more sugar” he says, mixing everything with great seriousness. And in the end his dish becomes a chocolate cake made of earth and imagination.
He is there to observe it Aki Sinkkonenscientist at the Natural Resources Institute Finland, who watches every movement with a knowing smile. Here, at the Humpula childcare center in Lahti, north of Helsinki, children can get dirty and much more.
Across Finland, 43 preschools have received funding to “renaturalize” their playgrounds and increase children’s exposure to the microscopic biodiversity — fungi, bacteria, invisible organisms — that characterizes soils and forests. This is not an aesthetic whim, but a surprising scientific project: recreating a small piece of forest in a school to improve children’s immune systems.
External biodiversity and internal biodiversity: a vital link
For years we have known how essential being outdoors is for the little ones. But today science goes further. Research has found that there are two levels of biodiversity:
- the external one – plants, animals, soil, water, microbes of nature
- the internal one – the microorganisms that live on the skin, in the intestines and in the respiratory tract
And the two worlds communicate continuously. In the first 1,000 days of life, this dialogue is crucial: the immune system learns to distinguish what is harmless from what is dangerous. If you spend too much time away from nature, this process can alter, increasing the risk of allergies, dermatitis, asthma and autoimmune diseases.
Bringing the forest to kindergarten
At Humpula Kindergarten they brought nature inside, literally. They created a large vegetable garden managed by the children, built a wet area and inserted trees and plants selected for their rich microbial biodiversity.
Additionally, they transplanted a huge carpet of “forest floor,” complete with blueberries, mosses, roots and small insects. Here children climb, dig, smell, taste, pick berries, play with branches and stones. And above all they get dirty. Very much.
The research: fewer pathogenic bacteria, more immune defenses
The study — the first of its kind in the world — involved 75 children between 3 and 5 years old in 10 nursery schools. For two years researchers analyzed:
comparing “renaturalized” kindergartens with traditional ones, covered with concrete, rubber or gravel.
The results after one year were remarkable:
And the effect was very rapid: in just 28 days, the immune system had already shown improvements. Other research has shown that playing in a simple sandpit enriched with garden soil improves immunity in two weeks.
Because it happens
Our body is home to trillions of bacteria and fungi, which are essential to our health. Nature, with its biodiversity, enriches our microflora through:
According to the theory of “old friends“, humans have evolved together with microorganisms in soil and plants. Depriving children of these allies means leaving their immune systems without instructions.
A revolution that is spreading
The success of the Humpula kindergarten has inspired other centers. In Helsinki, the nursery Poutapilvi-Puimuri is completely transforming the courtyard thanks to public funding and will soon have trees, grassy areas, sandboxes and much more.
In the UK, a Sheffield school installed a 70-metre hedge around its playground to reduce traffic pollution. After six months, nitrogen dioxide had decreased by 13%.
These preschools remind us of a simple and powerful truth: the health of children depends on the health of ecosystems. When we bring nature back into their lives — alive, complex, imperfect — children become more resilient, more curious, more peaceful. Perhaps the recipe for growing healthier had always been under their feet: a handful of earth, fresh leaves, a bit of sun, freedom to play and the return of the forest to their days.
