 FAR LEFT: Strobilanthes dyeranus and Lantana ‘New Gold.’ MIDDLE: Duranta erecta ‘Aussie 2000.’ FAR RIGHT: Mussaenda erythrophylla. With the constant clamor for landscape color, coupled with a desire for tough, high-performing plants, it shouldn’t come as a surprise to anyone that tropical plants are in. Whether you call them tender perennials or temperennials or even annuals, these plants all have their roots, so to speak, in the tropics. If you think these plants aren’t tough just because they aren’t cold hardy, think again. No matter how hot the summers get, these hot-blooded green machines will daily deliver good-looking foliage (which is often times highly colorful) and non-stop flowers until the consumer or the first freeze of fall takes them out. At Paul J. Ciener Botanical Garden (PJCBG) in Kernersville, N.C., these tropicals are relied on to saturate the formal garden with color throughout the summer and fall months. PJCBG’s Garden Curator, Adrienne Roethling, expertly and artfully arranges beautifully contrasting textures and complementary colors with ease. Even old standbys such as Persian shield (Strobilanthes dyerianus) can be enlivened when paired with another classic, Lantana ‘New Gold.’ This combination creates a beautiful duo of purple and gold, colors that always work well. And yet, this example also illustrates the importance we place on plants with exciting foliage. Flowers are glorious whenever they are present, but foliage lasts no matter the flowers that come and go.  Coleus ‘Paisley Shawl’ColeusTalking about foliage in tropical plants, you can’t ignore the plethora of beautiful coleus (Solenostemon scutellarioides) cultivars that continue to be developed. Everyone has their own personal favorites, but for me, I am excited by them more when they are grouped with other plants rather than when they are bedded out in masses. In this regard, Roethling has excelled in creating dramatic plantings at PJCBG. Coleus can be used in a number of non-traditional ways.
 Galphimia glauca Copper plantsAnother group of tropical plants with great foliage is the copper plants (also called copper leaf), the many cultivars of Acalypha wilkesiana. I grew up seeing these used to great effect at the Ira Nelson Horticulture Center in Lafayette, La., in the 1980s, and ever since then, I’ve been in love. Although copper plants are generally not small-statured, they are great for adding height and bold-textured foliage to the summer garden. Plus, they can take a hard pruning if they are outgrow a site. Classically, copper plants are best known by the cultivars with copper-tinted foliage. At PJCBG, a mass planting of tall, large-leaved ‘Haleakala’ and ‘Brazen’ were used to set off the small-leaved and compact-statured ‘Inferno’ in front. If you don’t care for these bright colors, most of the leaf forms you see in copper (e.g., ‘Obovata Cristata’) can also be found in green, too (e.g., ‘Hoffmanii’). Just don’t plant copper plants too early, as they strongly resent temperatures below 50°F, especially cool soil temperatures. Don’t forget the flowers  Mussaenda erythrophylla, Coleus ‘Watermelon’Here are a couple of exciting tropical shrubs that can be effectively used as tender perennials in temperate zones. Red flag bush (Mussaenda erythrophylla, sometimes seen incorrectly listed as Mussaenda coccinea), is a fabulous continuous blooming shrub. The flowers are bicolored, this effect is produced by the contrasting tubular corolla and the calyx, of which one sepal is enlarged and bract-like.Mussaenda erythrophylla has a white corolla with an enlarged fire-engine red sepal. This plant can be discerned at a great distance because of its showy blooms. Although it may be hard to see the resemblance to gardenias in this plant, take a look at the southeastern U.S. native Pinckneya bracteata (fever tree), and you’ll quickly see the family ties. Grow red flag bush in a bright sunny setting in well-drained soils. Poor soil drainage will result in foliar iron chlorosis. Other Mussaenda are grown, including white-sepaled species, but the nomenclature of plants in cultivation is highly confused.  Acalypha wilkesiana ‘Obovata Cristata’Golden thryallis (Galphimia glauca) is another flowering machine, this plant being popularly seen in southern Florida as a landscape subject. Although it is not as easily propagated as other tropicals, it is well worth acquiring (preferably in larger sizes due to its slower growth rate) and used because of its constant parade of bright yellow flowers. Golden thryallis does possess some minimal cold hardiness, a factor which can be exploited in fall plantings, with the evergreen leaves surviving the first frosts until temperatures drop below circa 27°F. Oldies but goodies I’ll highlight three examples which tell stories of where we’ve come with tropicals. The first two are in many ways old standbys of the Deep South. These are plants that I knew from my childhood in southern Louisiana as “old-fashioned” has-beens – Duranta erecta (golden dewdrop or Brazilian skyflower) and Tradescantia pallida (purple heart or setcreasea). Duranta certainly has come a long way since the 1970s, with a plethora of gold-leaved, variegated and picotee-flowered cultivars now available. One plant that I found in Japan in 2005 was given to me as Duranta erecta ‘Aussie 2000’. It had reverse variegation that I had not seen before, with gold-centered/green-edged leaves borne on a highly compact frame (compared to typical forms of this species).  Acalypha wilkesiana ‘Hoffmanii’Much new information has also been learned about Tradescantia pallida. It is generally now accepted that this species is perfectly root-hardy in USDA cold hardiness Zone 7. With this realization it is now possible to use the many new beautiful cultivars of purple heart (not all of which have purple leaves) as herbaceous perennials in Zone 7 and warmer. One of my favorites is the relatively newly named Tradescantia pallida ‘Pale Puma,’ a plant I suspect may actually represent a hybrid between T. pallida and T. sillamontana (white velvet). Pentapetes phoenicea, commonly called “copper cups”, is a true annual introduced by Thomas Jefferson to Monticello in 1811. This annual, somewhat related to cacao, is also being rediscovered for its upright form and alluring red-orange flowers. F. Todd Lasseigne is executive director, Oklahoma Centennial Botanical Garden, Tulsa, Okla., Todd@ocbg.org. |
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