Rob, wild mustard—which grows everywhere naturally in Napa Valley come spring—is a member of the brassica family of vegetables (including broccoli, cabbage, brussels sprouts, kale and other healthy vegetables). Mustard plants break down into a kind of natural nematicide that helps protect vines from destructive nematode-caused viruses like fanleaf disease (which wreaks havoc on grapevines). Mustard also helps with soil drainage. (Alas, the mustard in the Napa Valley is not generally made into actual mustard to slather on your burger.)

—Karen