Over-The-Edge Beauty

By William Scheick, Contributing Editor

Generally we want our plants to grow upward and outward. With groundcovers we hope for horizontal spreading — the sooner, the better. Sometimes, though, we seek out plants that can be directed downwards to dangle attractively over edges or borders. These plants are known as trailers, spillers or cascaders.

Such plants tend to be popular choices for hanging baskets, a setting I do not find easy to maintain during our long, desiccating, triple-digit summers. Even so, my local nurseries apparently have no trouble selling hanging baskets of draping million bells (Calibrachoa) each year, although I don’t know how buyers manage to keep them vibrant beyond early spring.

Trailing fuchsias are even worse, in my experience. I have had plenty of success, however, with other trailers spilling over containers set on the ground in dappled light beneath trees and also over the stone or brick sides of raised garden beds located in part-shade.

Easy-to-keep trailers

Readily available at plant retail outlets, silver ponyfoot or silver nickel vine (Dichondra argentea) is an enormously popular creeper serving as a groundcover or a “flowing” trailer.

 

Its silvery foliage is designed (like that of our native purple sage) to survive considerable sun exposure, even if part-shade is welcome. Silver ponyfoot tends to remain evergreen in most of our state. My neighbors often use this fast-growing Texas native perennial to cascade gently over container edges. It is even more dramatic when arrayed over rocks or low walls. It sets roots effortlessly when its leaf-nodes (along 3-4 four foot stems) touch draining soil.

Equally easy to find and keep is trailing lantana (Lantana montevidensis). This South American native spills delicately over the edges of pots, gravel, stones and walls. Mine spreads several feet onto river rocks, thrives in heat and endures long periods of dryness and neglect. Even so, it blooms profusely (purple, white or purple-white) from spring through early winter, especially after rainfall. Most of mine die back during winter, while some always remain evergreen, particularly adjacent to my south-exposed home foundation — a micro-climate where some of these trailers continue to bloom even when surrounded by icy snow.

Trailing silver sage (Salvia chionophylla) is a scrambling, thin-stemmed perennial that expands and roots with ease in moist, fertile soil. Such quick rooting behavior results from this Mexican plant’s restricted opportunities as a native of the Chihuahuan Desert. Simply put, it’s an opportunist in the presence of moisture. Yet it remains at heart an extremely water-thrifty desert plant and a good gardening choice for our state.

Its sun-managing ashen leaves (similar in hue to purple sage and silver ponyfoot) account for this plant’s nickname, snowflake sage. Trailing silver sage bears bright blue flowers during summer, while during winter it dies back to the ground when temperatures drop into the 20s.

Another of my favorite reliable trailers is creeping rosemary (Rosmarinus officinalis ‘Prostratus’). Evergreen, aromatic (piney) and low-spreading, this woody perennial will pour abundantly, yet gracefully, over the edges of walls and raised beds. A little pruning for shape is usually required. Its bright blue flowers are a summer bonus, and its needle-like foliage (restricting moisture-loss) can withstand our hot winds and temperatures.

In Texas this bush performs best in part-shade (with at least four hours of direct sun exposure) and in soil with good drainage (to avoid root rot). Creeping rosemary can tolerate drought up to a considerable point, but benefits from watering, as needed.

Fleshy-leafed trailers

The fleshy, narrow, burgundy foliage of purple heart (Setcreasea pallida; previously Tradescantia pallida) has long been a reliable standby that thrives in our heat and sunlight. A tough and fairly rapid grower, this Mexican perennial is often utilized as a trailing ground cover. But it can dangle Zilker Botanical Garden in Austin.

With somewhat stiff shoots, it is not as graceful as creeping rosemary or trailing lantana, in my opinion, and its royal luster dulls in too much shade. Purple heart roots quickly at leaf-nodes along stem-cuttings — just ask a neighbor for a few pieces — and pruning will curb shoot-legginess.

Although so-called ice plants are often used as ground covers, many of them also make excellent trailers. They come with good news and bad news. The good news is that ice plants produce colorful blooms and are succulents that are not only water-thrifty but also adaptable to our hot settings. The bad news is that ice plant species and hybrids vary in their performance and needs but (unfortunately) their taxonomic identities are in dispute among experts and (unsurprisingly) their labeling at plant outlets tends to be less than adequate.

A certain amount of trial and error might be necessary when gardening with ice plants. But since so many of them trail naturally, just look for small-leafed selections already splashing out of their pots, such as heartleaf ice plant (Aptenia cordifolia), which also comes in a variegated variety.

Moss rose also comes in a wide variety of selections. For trailers look for fleshy-leafed cultivars of Portulaca grandiflora, such as ‘Happy Trails Rosita’ and ‘Mojave Yellow.’ Portulacas can really take our sun, bloom dazzlingly in our heat and don’t mind poor soils (as long as they drain well). Trimming stem-tips fosters branching, which in turn results in more flowers.

Overwintered trailers

Besides portulaca, there are other annuals (or tender perennials grown as annuals in Texas) that provide colorful cascaders: nasturtium, trailing petunia, alyssum, trailing snapdragon, wooly thyme and (Texas native) creeping zinnia, for examples. Also look for these pendulant beauties: trailing verbena, creeping moss (phlox), torenia and trailing lobelia. I hate losing tender perennials and often will make special efforts to over-winter them, including the following three.

• Ivy-leaf pelargoniums (commonly called geraniums) are appealing substitutes for actual ivy. Not that there’s anything wrong with ivy (Hedera) as a cascading plant in places where it cannot become invasive. In fact, ivy makes minimal care-demands and often comes in varieties that are quite modest in behavior. Ivy-leaf pelargoniums, though, offer flowers as well as attractive dangling foliage. How far down these pelargoniums will “fall” varies among cultivars — somewhere between 1-4 feet. To look their best in Texas these plants need adequate water, soil that retains moisture and bright shade.

• A tougher tender perennial that endures more direct sunlight is sweet potato vine (Ipomoea batatas). This quick-growing tropical plant, now available in many leaf shapes and colors, has become very popular. Perhaps lime-green ‘Marguerite’ is the bestseller of the lot, though I am partial to burgundy ‘Sweet Caroline Raven.’ Sweet potato vines love heat and hold on during drought, but do need occasional watering. In the Austin area, to my surprise, in-ground sweet potato vines survive winters without protective intervention. They merely die to the ground and resprout in the spring. It’s dicey to count on this, yet it has been occurring with some regularity.

• Less tough, yet highly adaptable, is creeping Jenny (Lysimachia nummularia), a long-stranding houseplant favorite. It’s a perfect shade choice that requires good potting soil, some water and little else. Its small leaves are usually green, while ‘Aurea’ is a yellow-leaf variety. My creeping Jenny stays evergreen in dappled shade and survives Austin winters for a couple of years when covered by two blankets during freezes.

Unusual trailers

Perhaps the most unusual trailing-plant scheme I ever saw was a raised bed of St. Augustine grass with numerous “runners” (stolons) dangling over the edge like a silent green waterfall. Visitors to my yard have used the word “unusual” in reaction to my use of dangling spider plants (Chlorophytum) as in-ground trailers on inclines and over stacked pavers. This tropical houseplant spreads itself, toughs out our summers beneath live oaks and withstands Central Texas winters on its own despite having an official cold hardiness rating that suggests otherwise.

It has turned out, too, that my pink jasmine (Jasminum polyanthum) is also pretty tough despite its exquisitely delicate appearance. Its abundant and highly fragrant pink flowers bloom in late winter or early spring, and its appealing slender vines will twine upwards, sideways or downwards — however you wish to direct them.

It easily withstands drought, but performs less than ideally without occasional watering. Some of mine gets too much shade and then does not flower much. Besides pink jasmine, other twiners can also be made to weep, including blackeyed Susan vine (Thunbergia) and cup-and-saucer vine (Cobea).

For short-term beauty (unless overwintered), the right cultivar of fan flower (Scaevola) can make a beautiful procumbent or spiller when planted in draining soil situated in dappled settings. This Australian plant flowers abundantly in our heat and humidity, but needs water to prevent foliar damage. I mention “the right cultivar” because some fan-flower selections tend to get bald in the center of their bloom-heads. However, according to Jimmy Turner, former senior director of gardens at the Dallas Arboretum and new director of horticulture operations for the Royal Botanic Garden Sydney, ‘Surdiva’ varieties can be counted on for a full covering of blossoms without baldness.

Finally, various plectranthus selections are worth consideration as unusual trailers. Creeping Charlie (Plectranthus australis), for instance, offers dangling fleshy leaves — deep, rich green beautifully margined in white. This perennial, also known as Swedish ivy, can be overwintered and guarantees plenty of oohs and aahs from neighbors.

William's words of wisdom

• Creeping Charlie (or Swedish ivy) is an unusual but gorgeous trailer.
• A quick-growing tropical, sweet potato vine comes in many appealing leaf shapes and colors.
• Aromatic and low-spreading, creeping rosemary (above) pours abundantly, yet gracefully, over the edges of walls and raised beds. Silver ponyfoot (below) is a popular Texas native creeper serving as a groundcover or trailer.
• Portulacas can really take sunlight, bloom dazzlingly in heat and don’t mind poor soils
• An old houseplant favorite, creeping Jenny thrives in shade and can be overwintered.
• Spider plants (shown here in late December) will grow year-round in the ground and drape over inclines and edges.
• Many ice plants are water-thrifty and adaptable to our hot settings.
• Purple heart has long been a reliable trailer that thrives in our heat and sunlight.