It's the little things that make the difference for a livable city. And that is what makes the Tree-Fest unique. That we can all actually make a direct contribution to a healthier living environment by planting about 500 trees in the food forest of Mijn Stadstuin . greenSand helped with potting soil to allow the young trees to grow up healthy and to clean up more CO2. greenSand potting soil and garden soil contains finely ground olivine. It counteracts acidification of the soil and provides dosed nutrients. Optimal for a balanced root structure and a healthy start for young trees.