Minecraft wiki entry for Flower_farming, associated text: To grow flowers, you can use bone meal on a grass block. The block must either have no block above it (which is obstructing sun / moonlight), or be lit with a light level of at least 8. Flowers and tall grass will spread over grass blocks up to 7 blocks away in both directions (a 15×15 square). However, approximately 95% of growth occurs within a 4-block radius (a 9×9 area) around the source grass block.