A Gardening Journal

Paraguay Nightshade & Friends

No garden should be without ornamental potatoes. No, not the ones with fancy tubers: They're ornamental on your plate, not in the garden. Rather, ones with showy foliage, flowers, or fruits—or scary-wonderful thorns.

 

Here's another of the floriferous species: Paraguay nightshade. Purple-indigo flowers tip almost every stem in active growth, and if you grow the shrub year to year, you can train it into a standard (see the trunk of mine, below) or even a small tree.

 

Lycianthes rantonnetii Royal Robe blossom 091316 640

 

Keeping Lycianthes rantonnetii in active growth is key: The flowers are borne at the tips of only the youngest stems. Keeping the shrub in flower is also important because the foliage is notably lackluster, even strikingly so. (There are a couple of cultivars with variegated leaves that I'm eager to try. See "Variants," below.) Growing the shrub as a standard is another way to create interest independent of the bright flowers and despite the boring foliage. Then the plant is notable for having a rounded canopy atop a trunk.

 

I believe that my Paraguay nightshade is the Royal Robe cultivar, whose flowers are darker and more purple than the bluer flowers of the straight species. I grow mine is a pot, and can place it where it looks best. I chose this year's spot—at the side of a wide walkway—in haste, and with an eye simply to providing the sun the shrub adores, and to displaying its form as a standard. Below, flowers spangle the tips of a branch dangling near the standard's trunk.

 

Lycianthes ranonnetii trunk and trailing stem 091316 640

 

Over the Summer, the growth of the standard and its near neighbors maximized in the heat. Happily, these other plants also flowered, and in astonishing contrast to the nightshade. Here's a bloom of the nearby white swamp mallow, Hibiscus coccineus 'Moon Moth'.

 

Lycianthes rantonnetii Hibiscus coccineus Moon Moth 0913160 640

 

The species just misses being reliably hardy in southern New England, so I also grow it in a pot that, handily, was right by the potted nightshade. Nearness certainly intensifies the contrast in the sizes of their blooms. Size doesn't relate to success in being pollinated and, because the parts of a flower usually don't contain chlorophyll, producing a flower costs the plant energy. Smaller flowers could be more efficient if the preferred pollinator will still visit. Bees visit the hibiscus flowers regularly, and I've also seen them pollinating other enormous flowers in the garden, such as magnolia, and lotus.

 

Hibiscus coccineus Moon Moth 091316 640

 

But I've also seen bees going wild for the grubby little flowers of dwarf Chinese banana. Bees typically pollinate the medium-sized flowers of plants in the potato family, too, so I'd expect that they also visit flowers of Lycianthes rantonnetii.

 

Given the extraordinary size of hibiscus flowers, I can't help but wonder how it's worth it for the plant to produce them. Perhaps because the flowers occur only late in the season during which the plant has been growing vigorously, there's energy to burn. In their own ways, the magnolia and lotus follow the same strategy: Flowers of Magnolia grandiflora do emerge steadily throughout the season, but only a few at a time. Flowers of Nelumbo nucifera are few and produced just once a year.

 

Paraguay nightshade could flower constantly where temperatures remain hot; a full-sized shrub could bear hundreds of new blooms a day. With flowers that profuse, and borne month after month, it makes sense that individual flowers would be smaller.

 

At the bottom of the picture below, two other plants are seen flowering very close to the Lycianthes. Both bear profuse flowers, both of which are so small that a single nightshade bloom is as large in comparison as the hibiscus flower is to the nightshade flower.

 

Lycianthes rantonnetii Hibiscus coccineus Moon Moth Verbena bonariensis what closer 091316 640

 

Below, the complex flowerhead of a small-flowered form of Verbena bonariensis. Like Lycianthes rantonnetii, this species can be in bloom for months. It's a self-seeding annual this far north, but in the subtropics and tropics, it's a self-seeding perennial that could be in bloom much of the year.

 

Verbena bonariensis with hand 091316 640

 

The flowers are minute! 

 

Verbena bonariensis with hand 091316 cropped 640
 

 

Even at the highest magnification my camera lens offers, it's only just discernible that each flower has somewhat of a snapdragon look, with an upper hood-like petal above a lower landing-pad petal. Verbena bonariensis flowers are more typically a bit larger, and with four petals; regardless of the ultra-lilliputian scale borne by this form, bees still visit. Such tiny flowers don't offer much pollen or nectar individually, but a single plant could bear eight or ten such flower clusters, with another hundred or two individual flowers opening daily. It might be just a snack for a pollinator, but it must be worth the stop: This colony of Verbena bonariensis has been a formidably fecund self-seeder for years. 

 

Verbena bonariensis with hand 091316 highest res 640

 

The fourth plant is still a mystery; look again at the bottom of the picture below.

 

Lycianthes rantonnetii Hibiscus coccineus Moon Moth Verbena bonariensis what closer 091316 640

 

Tiny flowers earlier in the season have matured to just-as-tiny seed heads held like beads on long stems. See the ragged, pointed, rugose green leaves just below the stems of seeds? This plant was a volunteer, even a weed, but it isn't a grassy one.

 

Mystery Plant Two 640

 

This late in the season, nearly the entire plant—seed heads, stems, and much of the foliage—had become covered in powdery mildew. Most of the leaves really weren't pretty, but the seedheads and stems had turned a sophisticated dusty purple that meshed with the purple, lavender, and white of the Lycianthes, Verbena, and Hibiscus.

 

Mystery volunteer thats probably thought of as a weed 091316 640

 

Neither me nor my colleague plant geeks have a clue about this plant's identity.  Any suggestions?

 

Below, a group shot. The irregular canopy of Lycianthes stems tops a four-foot trunk; the Moon Moth hibiscus flower is on a stem more than six feet high. For this 6'3" gardener, both are conveniently at eye level. 

 

Lycianthes rantonnetii Royal Robe overall Hibiscus coccineus Moon Moth Verbena bonariensis WHAT 091316 640

 

The Hibiscus flower is merely large, not gigantic; the Lycianthes blooms are small and, if just a scattering of them is present (as is the case here), not very showy. Although their stems are three to five feet tall, the tiny Verbena flowers and mystery-plant seeds are still barely noticeable.

 

The curb appeal of this ensemble only registered when the traffic had slowed down. Happily, by high Summer, I was able to stroll through the garden, not race—even to stop and discover more of the details that had been there for weeks already. Thanks to the display of these four plants, I could see that, from a plant's perspective, a flower just millimeters across can be just as successful as one as large as my hand.

 

 

Here's how to grow Paraguay nightshade:

 

Latin Name

Lycianthes rantonnetii 'Royal Robe'; also known as Solanum rantonnetii 'Royal Robe'.

Common Name

Paraguay nightshade, which sounds exotic as well as rightly cautionary: All parts of Lycianthes rantonnetii are poisonous, as is the poisonous nightshade, Atropa belladonna. The shrub is also known as blue potato bush, which seems confusing: Is the shrub also forming underground tubers that are blue?

Family

Solanaceae, the Potato family.

What kind of plant is it?

Lycianthes adopts different habits depending on the climate. In Zone 11, it is a scandent evergreen everblooming shrub.

 

In Zone 10, frost is rare and the weather for much of the year can be hot; there, too, Lycianthes is usually evergreen. It can flower sporadically throughout the year but most heavily in the hot months of Spring to Fall. If weather turns cool or even frosty in the Winter, some or all of the foliage can be shed; growth resumes with arrival of warmer temperatures.

 

In Zone 9, frosts and—for such a heat lover—comparatively cool weather are to be expected, so Lycianthes flowers mainly in the Summer and can become deciduous in the cooler months. If frost arrives, tip damage or even dieback to the ground can occur. Then Lycianthes can behave more like a perennial, resprouting from the base and flowering that same Summer.

 

In these responses to varying amounts of heat and (mild) cold, Lycianthes behaves like other subtropical "woodies" such as Manihot grahamii and most forms of Abutilon.

 

When provided with frost-free circumstances and sufficient support, the flexible young stems of Lycianthes are easy to train. In uniformly hot circumstances, they become thick and woody enough to permit training a small free-standing tree. See the second "How to handle it" box, below.

Hardiness

Zones 9 - 11. 

Habit

Sprawling and broadly bushy unless trained. See "How to handle it" and "Quirks" below.

Rate of Growth

Fast.

Size in ten years

Six to eight feet tall and wide—but stems that touch the ground could root and enable the shrub to grow much wider. Lycianthes rantonnetii normally receives training that limits size. Unchecked growth is usually not the best choice because the shrub's loose habit and vigor combine to create a mood of weediness despite what can be a heavy display of flowers. In a hyper-orderly context, however, the perception of this habit could change from weedy to charmingly informal or even blessedly free-spirited. See "Partner Plants" and "Where to use it," below.

 

In this combination of glorious flowers but almost too vigorous habit, Lycianthes is similar to Bougainvillea.

Texture

Dense, especially when it receives regular pinching back and pruning; see the "How to handle it" and "Quirks" boxes below.

Grown for

its flowers, which are classic for plants in the potato family: The petals are fused into a small but brightly-colored trumpet with a very short tube and a wide, flat, flaring edge. They are borne at the tips of new growth so, as long as the shrub is in active growth, it will also also be in flower. Plus, the greater the number of active stem tips, the more profuse the flowers; if the shrub can be kept active year-round, it will flower year-round, too. See "How to handle it."

 

its toughness: Lycianthes loves high heat and strong sun, and tolerates some drought. Established shrubs growing directly in the ground are likely to be difficult to kill through neglect. 

 

its resistance to browsers: All parts of Lycianthes are poisonous. 

 

its ease of handling: If you want, pinch the stem tips regularly; if you forget or can't be bothered, the shrub will still look acceptable, and will still stay in bloom. If you forget to water regularly or cut the shrub back drastically at almost any time of the year, no problem: Lycianthes will bounce back from almost anything but poor drainage or excess water. See the "Culture" and "How to handle it" boxes below.

Flowering season

In New England, Lycianthes rantonnetii is used either as a one-season tropical or overwintered for outdoor display each Summer. In either circumstance, it's usually in flower from late Spring into Fall.

Color combinations

As is the norm for flowers with more than one color—in this case, violet and yellow—it's best when surrounding plants also focus on those same ones, albeit in different degrees of saturation. There's little need to bring in still more colors, and a real risk of creating a too-busy look if you do. If I had had a hibiscus that also flowered in yellow or violet, I would have chosen that instead of the pure white one in my shots above: White doesn't clash, but it doesn't actively engage, either.

 

See "Plant partners," below.

Partner plants

Provide a context for Lycianthes that emphasizes the deeply colorful flowers while helping finesse the shrub's boring appearance when out of bloom. The much larger flowers of Tibouchina semidecandra have similar coloring, and are usually present whenever Lycianthes is in bloom. Forms of canna with bright yellow flowers without conflicting spots are also possible; try King City Gold or Lofty Lanterns. Allamanda cathartica or Euryops pectinatus would be even more versatile, in that they are never out of flower as long as the weather is hot, and tolerate the same conditions that Lycianthes adores. Euryops can be grown either as a bushy groundcover or as a standard—as can Lycianthes. You could underplant the standard of one with the other that you've allowed to assume its natural growth habit as a groundcover.

 

Flowers that are dramatically smaller and are arrayed in spikes are even better. Any number of buddlejas, lavenders, rosemaries, penstemons, and salvias bear spikes of small flowers in shades of blue, purple, violet, or yellow; they also appreciate the strong sun and dry heat that Lycianthes does. Verbena bonariensis would be foolproof, too.

 

Because there aren't plants yet available with blue-to-violet foliage, closely harmonizing leaves will be in shades of yellow. Sword-shaped leaves will provide distinct textural contrast, too, and are often borne on plants that revel in heat and drought. Yucca filamentosa 'Color Guard' and Phormium 'Yellow Wave' supply the right color, but Yucca gloriosa 'Variegata' eventually forms trunks that keep their spiky heads of foliage above Lycianthes—which could, therefore, be used as a groundcover. If you can provide side-to-side planting spots where one is lean and dry but the other swampy, juxtapose Lycianthes with Arundo donax 'Golden Chain'. I grow both in containers—the pot of Arundo sits in a fifteen-gallon galvanized wash tub—so the pairing is easy.  

 

In subtropical and tropical climates, Lycianthes could be massed on the sunny side of flowering shrubs and trees with compatible coloring: for lavender to violet, consider Jacaranda mimosifolia.  For yellow, choose among Caesalpinia lutea, Caesalpinia pulcherrima 'Aurea', Delonix regia var. flavida, yellow cultivars of Plumeria rubra, Parkinsonia aculeata, and the yellow form of Spathodea campanulata.

Where to use it in your garden

A Lycianthes completely out of bloom is a dull thing, whereas one covered in bloom can be as prominently colorful as bougainvillea. Unless your circumstances are likely to ensure a heavy flowering, site Lycianthes to maximize flowering—see "Culture," below—and where whatever blooms it does have can be seen at close range. The surrounding dense and dull-green foliage is likely to mute any long-distance floral impact if only a few blooms are out.

 

Growing Lycianthes in a container is particularly helpful: The shrub can be moved to where the flowers, few or many, will have the most impact. In hot and dry climates, Lycianthes growing in full sun can flower so heavily it can be striking even at a distance. There they can be used as informal hedges and espaliers, as filler amid larger and more sculptural companions, as colorful standards, or as small ornamental trees. See the "How to handle it" and "Quirks" boxes below.

 

The shrub's vigor and billowing habit could be an asset where the prevailing geometry and tidiness is so intense that some casual or even disruptive obliviousness to boundaries would be welcome. Are you gardening in Zones 9 and warmer, and have a blazing-hot courtyard with wide expanses of paving? A rollicking colony of Lycianthes rantonnetii could be just the exuberant touch you need.

Culture

Full sun, all possible heat, and soil that is always well draining. Lycianthes tolerates drought when growing in-ground, which is a fortunate consequence of its requirement for good drainage; but it is more floriferous with regular watering. When growing in a container, watering needs to be more attentive, because the restricted root range of the container doesn't permit failsafe root growth even deeper or farther away to where the ground can provide additional moisture. Heavy soil or locations where water pools after rainfall are likely to be fatal.

How to handle it: The Basics

Lycianthes is a heat lover, so plant or transplant when temperatures are warm and likely to become even warmer. Even in the subtropics and tropics, this species is likely to establish more quickly when planted at the beginning of the hottest season of the year even if it is also the drier season. Plants that are merely heat tolerant would be planted at the start of the rainier season, which is also usually cooler, so they can establish all the more deeply in preparation for the onslaught of the coming hot-and-dry season.

 

Provide sufficient water for establishment. Pinch the tips of the longest stems Spring to mid-Summer whenever convenient to limit overall size and encourage denser growth. Deadheading isn't necessary.

How to handle it: Another option—or two?

As is no surprise for a shrub that is fast-growing and responds quickly to pruning, Lycianthes rantonnetii is versatile.

 

For groundcover, plant shrubs every four feet. For more compact growth, tip-prune several times during Spring and early Summer. For growth that is still somewhat compact but is looser, cut all branches back to a foot or so early in the growing season, and let the new growth lengthen freely. 

 

For a hedge, plant small plants every two feet; Lycianthes grows so quickly there's no need to plant larger sizes. Sheer soft growth regularly to maintain compact bushiness; for more informal settings, cut woody stems back early in the growing season, letting new growth lengthen freely.

 

For a standard or small tree, stake a long stem and allow it to grow as high as desired. Side stems usually appear naturally; encourage them by pinching the tip when the staked stem has reached the bottom of the desired canopy: Resultant stems will grow upward, too, not just outward. Pinch their tips regularly to keep the canopy compact as well as floriferous.

 

Lycianthes can also be fanned informally against a wall or fence; it can be woven through large mesh or lattice to make free-standing screens. Guide or tie soft growth as needed to achieve the desired height and width; pinch or prune breastwood regularly to keep the shrub from projecting too far from the supporting structure.

Quirks and special cases

Lycianthes stays active and floriferous when heat and light are sufficiently high. Because this shrub thrives in containers, even for the long term, you may want to overwinter one year after year. Space in sunny and frost-free shelter is usually at a premium so, when you bring your specimen indoors before frost, reduce watering and prune all stems back by half. If temperatures are cooler at night—fifty degrees is sufficient in my experience—new growth won't begin to appear until late Winter and, so, little watering will be needed for several months.

 

When growth resumes, increase watering only modestly. Pinch new stems regularly to keep the increasing size of the specimen to a minimum in an already-crowded environment, as well as to ensure a bushy and floriferous presentation when the specimen is returned to the garden after frost danger is past. If drastic reduction in canopy size is desired, wait to prune until the shrub is already in active growth—just a few weeks before returning it to the garden—so that new stems will appear quickly as well as profusely. If you prune stems back to their leafless stubs while the shrub is dormant in the Winter, regrowth can be spottier.

 

If you are growing Lycianthes at the colder end of its hardiness range, where occasional frosts and dieback are not a surprise, don't prune later than mid-Summer: You want any resultant growth to be fully hardy in time for the coming cool weather. Even then, prune only lightly, so as not to stimulate vigorous soft growth that will take longer to harden. Reserve major pruning until the start of the growing season.

 

When frost occurs, you'll know it: This shrub's foliage is evergreen in frost-free climates, and doesn't have a routine ability to shed foliage for the Winter as does, say, a maple tree. Instead, the foliage remains green and, as possible, active—and, therefore, vulnerable to frost. Cut off portions of stems with frost-damaged foliage just below the start of the damage; the frozen foliage is disfiguring, so you'll be motivated to remove the damaged growth sooner rather than later. 

Downsides

When successfully pollinated, the flowers mature to showy but poisonous red berries. In my experience, the flowers don't form fruit in temperate climates, perhaps because the preferred pollinator is absent. In subtropical and tropical climates, Lycianthes rantonnetii is not a shrub to grow where children could be tempted to sample the berries.

Variants

The flowers of the straight species of Lycianthes rantonnetii are satisfyingly intense in their blue coloring; those of Royal Robe are a bit more saturated and of a deeper hue but the difference seems subtle to me. The margins of the leaves of Lynn's Variegated are creamy white, while those of MonRita, which is marketed as Sunny Daze, are yellow. The flowers of both of these variegates seem to be the same hue as those of the straight species—but show up much better thanks to the contrast with their lighter-colored foliage.

Availability

Online and occasionally at retailers. Widely available where hardy.

Propagation

By cuttings as well as by severing from the mother plant stems that may have been low enough to rest on the ground and, therefore, take root.

Native habitat

Lycianthes rantonnetii is native to Brazil, Paraguay, Bolivia, and Argentina. It is named for Victor Rantonnet, a French horticulturalist.

 
 
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