Spring has sprung, and summer will soon arrive. If you’re a flower gardener—and the National Gardening Association estimates that members of more than a third of American households are—you already may have begun to till soil and plant seeds. If you enjoy gardens more by watching than working, however, now is the time to plan a trip to take in some of Mother Nature’s bountiful beauty. Gardens come in a variety of types, sizes, and offerings. Some are urban pockets of color and scent, others world-famous destinations that people travel far to see. They also can turn pages of history, amaze with their beauty, and at times amuse. Wherever you live—or go—there are no doubt parks and plots that can satisfy a longing for the splendor that flowers, shrubs, and trees provide. Many city dwellers live close to outstanding public gardens. Residents of Los Angeles have easy access to what …