Jane Kuhl gives her patio walls some punch with butterfly-friendly plantings in lightweight resin urns that have the look of cast iron. Steve Dodge made a single concrete urn the focal point of his formal rose garden. Whether arranged in groups or placed individually, such containers add a grace note to any yard, front entry, or even tabletop. And the curvaceous shape of these planters has been around for centuries: first in hand-carved limestone and marble and later in the Victorian era, in factory-produced cast iron and terra-cotta. Today’s concrete, fiberglass, and resin versions are less pricey, often lighter in weight, and more weatherproof.