Results from the MyGardenOfTrees pilot trials show that seed germination and early seedling survival vary strongly among micro-gardens, even within the same climate region. Much of this variation appears to be linked to fine-scale environmental differences, including local soil conditions. Our analyses identified soil properties such as nitrogen content and clay fraction as important predictors of germination success, alongside climate and provenance effects. Collecting soil samples from each micro-garden will therefore help us better understand why some seedlings establish successfully while others do not, and improve predictions of which seed sources are best suited to different local environments under future climate change.