Gardening does something to the brain that most hobbies can’t touch. University of Colorado Boulder researchers found that a common bacterium in garden soil, Mycobacterium vaccae, activates the same serotonin-producing brain cells targeted by some antidepressants — real, measurable happiness, delivered through nothing more complicated than soil and water and patience. My neighbor Peggy knew that better than anyone the day she knocked on our door with a shovel and offered, out of pure kindness and compassion, to help us turn a bare corner of the yard into a Halloween pumpkin patch. Neither of us had any idea that garden hobby would end up unearthing something her own late husband had buried there years before either of us moved in.