|By William Scheick
The Black Rose — a book title that stirs the imagination. While Thomas Costain’s 1945 bestselling historical romance is actually far tamer than my childhood memory of its earliest paperback cover, its title promises an enticing concoction of exoticness and passion.
The “black rose” in that book is a beautiful woman from the medieval East. A striking woman also figures in The Black Tulip, Alexandre Dumas’s now forgotten 1850s historical novel, which at least mixes romantic infatuation with a quest for the most exotic of flowers during the 17th-century Dutch tulip craze.
As these book titles suggest, black-looking flowers inhabit a class of their own. At once strange and desired, atypical and elegant, they command attention. It’s hardly surprising, then, that so-called black plants have become a horticultural phenomenon.
IS BLACK POSSIBLE?
But is black actually a floral possibility? No, Hans Kapiteyn has stated: “It is impossible to create a truly black flower.” As a Dutch bulb merchant, Kapiteyn should know. He spent 16 years breeding a recently introduced black hyacinth named ‘Midnight Mistique.’
It isn’t hard to understand Kapiteyn’s point. The floral hues we see are those spectral bands (wave lengths) that get reflected back to our eyes because they are not absorbed by the petals. A yellow rose, for example, absorbs all the bands of visible light except yellow, which is the reflected color we see.
How do some flowers appear to be black? The impression of blackness in plants, biology professor David Lee has explained in Nature’s Palette: The Science of Plant Color (2007), results from oxidation, variations in acidity, odd cell shapes, tannin and particularly unusual molecular concentrations. These features can combine pigments in ways that absorb the spectral bands more inclusively and more evenly than are typical for most flowers or leaves.
The result, in short, is an optical illusion — an impression of blackness. Studied closely in bright light, however, a black-seeming flower (such as a ‘Queen of the Night’ tulip) usually reveals faint red-to-purple highlights. What appears to be black, then, is actually an extreme and uncommon manifestation of the dominant red pathway in flowers.
Confederate rose (Hibiscus mutabilis) is not considered a black plant. Despite its popular name, it’s not even a rose or an Old South native. But this heirloom perennial, so familiar to Texans, offers a lesson about the nature of black flowers.
As its species name mutabilis indicates, this plant’s flowers tend to “mutate” in color. Not all confederate roses bear flowers that dramatically change their hue, but those that do so open white or pale pink. Then within 1 to 3 days they sequence from pink to rose until they turn purple-blue before closing.
Even the darkest flower stage of confederate rose still expresses the red pathway — a fact that also becomes apparent whenever some so-called black flowers fail to be as black as advertised. That’s the case, for example, with Alcea rosea ‘Nigra,’ a hollyhock I once grew. At its best, its flowers appeared to be velvety black, but often in very bright sunlight its variable blooms revealed an underlying rosy-maroon tinge.
While the dark purple stage of confederate rose flowers never looks black, it does dramatize the function of changing petal-cell acidity levels in determining the appearance of so-called black flowers. The acidic pink-to-rose floral phase (when confederate rose flowers are maximally ready for fertilization) is designed to attract pollinators. As acidity decreases, H. mutabilis flowers turn purplish-blue — a clear signal to pollinators to skip such sub-prime blooms, no longer rich in nectar and pollen.
Which raises a fascinating question: why do any flowers appear to be black from the outset? It would seem to be a very poor form of advertising for pollinators, which tend to prefer colors. Even if, say, blackish flowers possibly appeal to the polarized vision of insects benefitting from the ultraviolet end of the spectrum, the precise function of such blooms remains unclear. And the fact that black flowers are rare in nature only deepens the mystery.
DESIGNING IN BLACK
If black flowers are rare in nature, they are not uncommon among plant breeders. In fact, plants with black flowers or foliage have become extremely fashionable.
They are more than fashionable, according to Karen Platt in Black Magic and Purple Passion (2004). Black plants, she has stated, have “transcended fashion to become a permanent part of the garden, just as black is a permanent part of most women’s wardrobes these days.” As a former owner of a black-plants nursery and as the founder of the International Black Plant Society, Platt enjoys an insider’s take on positioning solitaire or companioned black plants for eye-popping landscape effects. “Experiment,” she counsels, “the ultimate key to the success of a dark garden is the selection of plants with regard to tone, foliage, texture and form.”
Or think of designing with them as artwork, Paul Bonine has urged in Black Plants (2009). “Even an ordinary garden can be transformed by dark foliage and flowers into a canvas with the depth and play of light and shadow as detailed as a painting by a Dutch realist.” Except that, thankfully, designing with black plants isn’t as challenging as imitating a Dutch master.
The main fact to keep in mind about including black plants is their considerable power to draw the eye and steal the show. As a result, their bold effect often tends to suit larger settings better than smaller ones. Of course, container compositions are an exception to this advice. Some container black plants, including the hard-to-believe tropical bat flower (Tacca chantrieri) from China, will elicit involuntary oohs and aahs from visitors.
BLACK PLANTS FOR TEXAS
When it comes to design, perhaps most challenging is the placement of nearly solid-hued blackish plants, particularly if they are as large as purple-black cannas and elephant ears (Colocasia esculenta). Such plants can be used for high-impact contrast with other large plants sporting bright-colored blooms.
Smaller plants with dark foliage or flowers, such as the ‘Onyx Odyssey’ Lenten rose (Helleborus) suitable for North Texas, can be positioned among pastel-hued neighbors to create a more elegant effect.
Sometimes, too, blackish plants can be played off each other because their patterns, textures and sizes vary. So, for example, a coral bells (Heuchera) combination of ‘Black Beauty,’ ‘Midnight Rose’ and ‘Cowardly Lion’ offers fascinating variations on the theme of black. ‘Black Negligee’ baneberry (Actaea) is a possibility in East Texas.
It might be easiest to design with variegated black plants, which provide their own mixed palette. As ‘Eclipse’ coleus, ‘Iron Cross’ begonia, ‘Happy Violet’ pelargonium and ‘Cascade Creeper’ tiarella demonstrate, green and black patterns can be quite striking. Bright yellow or chartreuse highlights define ‘Polly’ alocasia, ‘Cowardly Lion’ heuchera and various variegated pelargoniums. For a “louder” effect there are plants that blend black with pink or reddish brown, such as copper plant (Acalypha wilkesiana) and ‘Tilt-a-Whirl’ coleus.
Perhaps it’s too unimaginative to mention blackberries and eggplants, which can get dark enough to appear black. Also, there are black cherry tomatoes. But ‘Black Pearl’ peppers are something else altogether. These peppers look so dark and silky that they seem utterly unreal. They always demand a second look, and even then it’s hard to believe they are not a black-magic optical illusion.