It's never too early to start thinking about your summer garden! Good gardeners know that a successful patch of flowers and veg takes year-round planning. As a rose-fanatic, one of my favorites is David Austin's English Roses. Austin, a British gardener, cross-pollinates old varieties of roses with both old and new breeds. The result is a gorgeous family of vibrant, hearty flowers with gorgeous perfumes. Best of all, the resilience of the old roses makes these low maintenance; pesticides and harsh chemicals need not apply.
In the same vein, I'd recommend The Complete Book of Herbs. This is a marvelous encyclopedia of herb lore, with details on how to raise specific plants, and loads of recipes and crafts that you can make from herbs. Everything from facial cream to mint lemonade is detailed in this copious book.
Finally, the ultimate classic: Thomas Jefferson's Garden and Farm Books. Scientist that he was, Jefferson detailed every success and failure of his carefully calculated gardens. A trove of marvelous advice - from how to mix special fertilizers, to coaxing warm-weather plants to health in colder climes - this is a great book for casual gardeners, historians, and organic enthusiasts alike.