To maximize the look of tropical, you almost have to use tropical plants from warmer zones.
Sure you can use big leaved hardy perennials, or add brilliant primary color, but the form of tropical plants is much harder to substitute if going for the island look.
The swaying palms, the vibrant hibiscus, the huge leaves of banana, Canna, Alocasia, Colocasia, and of course, the aquatic water lilies. Notice the palms at Longwood gardens above are in containers. It makes for easy storage in winter greenhouses. Also, what you don’t see is the plants that appear in the ground are also in containers to lift in fall.
Tropical exotic destinations are lush, dense and very green due to all the rain. Having traveled to Costa Rica, Maui, and St. Lucia, I was in awe of the height and girth of the healthy plants, all growing in close proximity to each other. Jungles are in these places for a reason.
Many of the named plants above can be grown indoors starting early March from bulbs, but it is always a lot of work to lift the plants to save them year to year – or even just save the bulbs. It is expensive to replace bulbs too, some being over $10 per bulb. While I admire gardeners who can create this backyard paradise each year in cold climates, it would never be something I would design or even suggest.
The cost alone makes it difficult to fathom. I have to say I do like seeing this look at both Longwood Gardens and Chanticleer. It really transports me back to places I enjoyed visiting.