The best-kept secret about tropical gardens is that not all the players need hail from exotic locales. Think large and dramatic foliage plus bold color, and you'll end up with hundreds of plants that are growable in your garden all year despite long, cold winters. Glossy ground covers with a lush habit include hardy arums and asarums. You can't beat Acanthus, Gunnera, or Rheum for leafy architecture, and all these perennials survive cold winters. The imposing leaves of catalpa and magnolia trees have a tropical feel, yet they're quite hardy. Dutchman's pipe, trumpet vine, and hardy passionflower display a junglelike vigor, and the vast bamboo and fern families number several cold-hardy species in their ranks.
Among succulents, sedum, sempervivum, yucca, and prickly pear cactus can weather cold winters. Melianthus, a fringed silvery shrub from mountainous Africa, ranks high on the list of tropical wannabes. It has an imposing structure and a crowd-pleasing color that makes it an outstanding companion plant. New Zealand flax (Phormium) has multicolor straplike leaves that make good focal points in tropical-theme borders. Some Phormium hybrids are hardy to Zone 7.
After the final frost in spring, plant showy annuals to fill gaps in a tropical-look garden. Use castor bean, plume poppy, and cleome for striking height or form. Annual vines grown from seed, such as purple hyacinth bean, scarlet runner bean, or black-eyed Susan vine, rise up quickly and entwine structures in junglelike lushness.
Houseplants that have languished on the windowsill all winter can also be exported to add color to tropical borders. Hibiscus, palm, and others bring Hawaiian-shirt shades and shapes into temperate gardens. Make an easy fall transition to indoors by keeping a group of potted houseplants on the patio or deck, or gather them in a corner of the garden that offers late-day shade.