There's a river guide named Tommy who took my family down the Colorado years ago. In the mornings, deep in the Grand Canyon with the walls glowing red above us, he would sing Guy Clark's "Homegrown Tomatoes." It's a goofy, perfect little song, an ode to the marvel of a ripe tomato, and it lands on a couplet that has stayed with me: only two things money can't buy, and that's true love and homegrown tomatoes. Tommy sang it like a man who meant it. What I heard in it, echoing off that ancient r...