After Novella Carpenter’s critically acclaimed memoir Farm City: The Education of an Urban Farmer came out, she and friend Willow Rosenthal, the founder of West Oakland gardening nonprofit City Slicker Farms, started talking about compiling a manual on urban gardening. “We always got these random emails like, ‘My chickens aren’t laying anymore!’” says Carpenter. So she and Rosenthal joked that they should write a book so they could reply: “Buy the book!” Three years later, they can. Their new book, The Essential Urban Farmer, is a 500-page nuts-and-bolts guide to farming in the city -- complete with sample garden designs, …