Plant one act of kindness in a garden and it behaves like a perennial: it keeps coming back, season after season, a little bigger every year. Science suggests even the smallest planting matters. In one Royal Horticultural Society study, researchers gave residents of a bare, gray street plants for their front gardens. A year later, the share of people with healthy stress-hormone patterns had jumped from 24% to 53%. A $1 backyard handed to strangers, a heart of daffodils planted for a crossing guard, a neighborhood feud settled over sunflower: these stories show this hobby grows far more than flowers. It grows kindness, and the happiness that comes with it.