Our eastern-U.S.-native Jacob's ladder is named for its many-lobed, pinnate leaves -- but the sky-blue flowers on 18-inch stems in mid-spring are the main thing if you're a gardener. It does especially well in moist, partly-shaded sites. Plants go dormant in summer. Propagated from plugs. Zone 4. 3.5-inch pots. Photo: Kristine Paulus, licensed under CC BY 2.0