The pedestaled, heavily embellished Grecian-classic vases better suited to gated estates than to backyard patios no longer define garden urns. From its material and style to its color, the garden urn of today can be as formal or trendy as you like. Molded fiberglass, resin, plastic and even wire urns now provide lightweight, strong and portable versions of concrete, terra cotta, ceramic or marble ones at a fraction of the cost. Planting an urn successfully depends not only on its material but on its style and final location.
The Three S's
Style, scale and surroundings all determine the best urn for a given location. Large gardens swallow small urns, and large urns overpower small spaces. Look for an urn that fits your house's architecture and garden layout. If possible, find one with drainage holes. If you can’t find one, substitute a traditional, well-draining planting pot sized to fit inside the urn. Plant it instead, and remove it from the urn for watering. Of course, this solution won't work for trees or large shrubs.
Plants for Urns
As a starting point, the general rule for planting urns is to use a tall, linear “thriller" in the center for height. Rounded or mounding "fillers" add fullness between the center and edges. Trailing “spillers” soften the edges and continue the thriller’s vertical line. Feel free to improvise. One or two spillers, for example, accent an elaborately carved urn’s embellishments, but several spillers blanket them. A coco-lined wire urn, on the other hand, benefits from masses of spillers hiding much of the liner. Vertical thrillers aren't required; a globe-shaped shrub gives a plain, square urn a strikingly contemporary look. Always use plants suited to your climate, and avoid mixing ones with different watering or fertilizing requirements.
Reduce a large urn's finished weight by filling it one-quarter full with lightweight material, such as packing peanuts or crushed aluminum cans, separated from the potting medium with fine mesh screening. For lighter urns or pots, put the mesh directly over the drainage holes to prevent soil from washing out. The University of Georgia Extension recommends blending a sterile, well-draining soilless potting medium with 5-10-10 or 5-10-15 fertilizer and dolomitic lime. For each 1 1/4 cubic feet -- a bushel-basket portion -- of medium, use 4 1/2 tablespoons of fertilizer and 6 to 7 1/2 tablespoons of dolomotic lime. In a wheelbarrow, mix enough of the amended medium to fill the pot or urn to within 1 inch of its rim.
Creating the Design
Water the plants well and set the thriller, still in its container, in the center of the pot or urn. Arrange the potted fillers and spillers around it. If combining foliage and flowering plants, add the flowering ones last to create the most vibrant color combinations. When the design is right, plant each at its original depth and tamp the medium gently to remove air pockets. Water until the excess water drains, wait 30 minutes and repeat. For a finished look, cover the exposed medium with moss. Check your plants daily and water again whenever the medium is dry to the touch. In hot or windy weather, small urns may need watering twice each day.