In tropical and sub-tropical regions such as most of the southern United States, the hottest part of summer is a time to move into the shade. But retreating to shade does not mean kissing summer color goodbye. A number of tropical plants bloom very well in full shade. These plants can typically be found in the wild growing along rivers and streams, or in the under-canopy of tropical jungles.
New Guinea impatiens were introduced to the United States in 1972, and have steadily grown in popularity since their introduction. In the wild, the plants grow along stream beds in New Guinea. They prefer full shade and moist conditions, and can form low mounds that may reach up to 2 feet. Colors range from red, pink and white to variegated colors. The plants are typically grown as annuals, although they are actually short-lived perennials with a 2-year lifespan. You can propagate impatiens from rooted cuttings.
The hosta plant, also known as plaintain lily, is typically grown for its interesting foliage, but the plant is actually a flowering variety of the lily family. Because the hosta grows in temperate climates as far north as USDA hardiness zone 4, it can be used to bring a tropical feel to northern gardens in this zone. The flowers of hosta are produced on stalks as tall as three feet that poke above the leafy vegetation like antenna. Though many gardeners keep the flowers cut back so that hostas will put more energy into leaf production, you can leave the small purple flowers intact.
Crossandra is frequently called firecracker flower in southern gardens due to the way that the flowers' color jumps out of shady areas like a fire cracker explosion. Crossandra is distantly related to Mexican petunia, although it comes from India. The flowers come in orange, salmon, red and yellow, and bloom from spring to fall. In California, gardeners plant crossandra in full sun. But throughout the southern U.S., gardeners plant it in partial to full shade to protect it from summer heat. The plant likes a little morning sun, but it also does well when combined with traditional shade lovers such as hosta or begonia.