Exotic Annual Vines by Rita Pelczar

Add a few of these climbers to your garden and its ambiance instantly takes a tropical turn.

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Since summer in southern Maryland, where I garden, does a pretty good imitation of the Tropic of Cancer, it isn’t surprising that so many tropical vines seem at home here. Most are perennials in their native clime, but they grow here as annuals. Choices among tropical climbers are many—narrowing the selection is the real challenge. In one way, it’s fortunate that the vines usually don’t survive our chilly winters—that means new vines can be sampled each year.

Supporting Lazy Habits

A vine’s stems lack the rigidity to stand upright. They need some external support to grow upwards, and only gravity to grow down. Given their lax growth habit and wandering nature, planning is essential before you plant a vine in your garden. Lazy of habit they might be, but they are plants on the move! Determine in advance where you want your vine to grow and how this growth will be supported or it may become a nuisance.

Vines have developed several strategies to climb, which affects the type of support they need. Some vines cling to a flat support, like a wall, with aerial roots or specialized adhesive tendrils. Others simply lean on or droop over nearby structures or plants. And some vines climb by twining their stems, leaves, petioles (leaf stem), or tendrils around whatever is handy.

The vines we grow as annuals are, for the most part, twiners. A trellis, fence, obelisk, mailbox, lamppost, porch railings, even strings tied to a sturdy overhead support, provide the necessary framework for accommodating their aerial feats. Look around your yard and you are likely to find a few potential vine supports. Or a wide range of freestanding supports can be purchased or economically constructed—bamboo poles work well.

If planted in a hanging basket, a twiner like black-eyed Susan vine or purple bell vine will wind its way up the hanging wires and cascade over the edge, producing several feet of vertical growth. You can also add tropical flair to a porch or patio by combining a vine in a planter with colorful annuals. Allow the vine to weave through the other plants.

Irresistible Ipomoeas

Some of the most beautiful and exotic vines are members of the genus Ipomoea. My favorite, without hesitation, is the moonflower (I. alba, USDA Hardiness Zone 12–15, AHS Heat Zone 12–10), a perennial twiner found in tropical regions worldwide. If ever there was a more romantic garden inhabitant, I’ve not met it. The six-inch pure white, silky flowers stand out against large, heart-shaped leaves. The blooms are so fragrant that you can tell when one is open well before you see it, and if you bring a freshly opened flower indoors, its perfume will scent an entire room.
The best thing about a moonflower is watching one open. Catch it at the right moment, sometime shortly after dusk, and before your eyes, its spirally folded, four-inch bud unfurls. Each flower lasts only one night, usually withering by mid-morning, but new buds open each evening.

Growing moonflowers could hardly be easier. Its seed needs a little scarifying—that is, filing or nicking the hard seed coat—followed by soaking overnight in water before you sow it, but once planted, it grows quickly. I sow mine directly in the garden, although you can start them indoors about eight weeks before the last frost. Don’t sow or transplant moonflowers in the garden until the weather has settled and the soil has warmed a bit.

Site moonflowers in full sun in rich, moist, well-drained soil in a spot where you can observe it up close, or near a window so its scent can be carried indoors. I grow mine along the front porch near the swing where we can watch its enchanting evening performance.

Although they are altogether different, the flowers of mina or Spanish flag (Ipomoea lobata, syn. Mina lobata, Zones 13–15, 12–10) are nearly as exotic as the moonflower. They are borne along one side of a curved, eight-to 12-inch stem. The flowers open from the base scarlet-red, maturing to orange, then yellow, then ivory. They persist a good while, so each stem features all these colors. I get impatient waiting for that first bloom to appear, which may not happen until early August, but once flowering begins, it is spectacular and non-stop until frost.

A native of the American tropics, mina’s culture is the same as moonflower, but wait until outdoor temperatures stay above 50 degrees Fahrenheit at night before moving plants outdoors—mina is extremely sensitive to cold. Once the seed germinates, stems grow rapidly to 15 feet, supporting a dense cover of three-lobed leaves. It grows well in containers or in the ground, and can easily be trained to a trellis or strings to serve as an effective screen.

Clock Vines

From the other side of the globe come the clock vines of the genus Thunbergia. The species most commonly found in gardens is the black-eyed Susan vine (T. alata, Zones 11–15, 12–10), a native of tropical Africa. It bears bright yellow, funnel-shaped flowers that are an inch and a half across, with five broad lobes and a contrasting center that is very, very dark.

Compared to many tropical vines, its stems are thin, with a very delicate appearance, and it is often grown in hanging baskets. But appearances can be deceiving. Last year, I decided to grow the variety ‘Blushing Susie’ with its shades of red, pink, and ivory flowers in a bed where I had placed a large weathered tree stump. I figured the stump would provide support and a pleasing weathered gray background for the colorful flowers. Once the vine took hold, however, it completely obscured the stump and continued to grow six to eight feet in all directions. It was a battle to keep it from overtaking surrounding plants.

This year, I will restrain it in a large pot. But if I needed a fast-growing screen, I’d plant it in the ground and hang strings or plastic mesh for its stems to climb. I’m tempted to try other varieties—like ‘White-eyed Susie’ with dark-centered white flowers or ‘Sunrise Surprise’ with flowers that range from ivory and yellow to apricot and rose—but I’ve decided the yellow flowers of the species with that intriguingly dark center are still the most dramatic.

Mandevilla

The genus Mandevilla consists of 120 or so woody stemmed twiners from Central and South America; several have become very popular in the past decade for use as summer annuals in temperate regions. All produce large, funnel-shaped flowers with five broadly spreading lobes. They are quite easy to grow, tolerating heat and producing flowers steadily from early summer to fall. They grow best in full sun in fertile, well-drained soil with a regular supply of water.

Mandevilla 5amoena ‘Alice du Pont’ (Zones 13–15, 12–1) is among the most popular varieties. Its four-inch flowers open a pale pink, deepening to rose-pink with a darker pink throat and sometimes a yellow eye. They are borne in clusters on robust twining stems that can grow to 20 feet. Similar in habit is M. splendens; its pink flowers display yellow throats. New hybrid Mandevilla selections include red flowered ‘Ruby Star’, ‘White Delight’ with white flowers that are blushed with pink, and the pink double-flowered ‘Pink Parfait’.

Mandevilla plants have become widely available at nurseries in spring. If you purchase one that has been growing in a greenhouse, acclimate it to outdoor conditions gradually once all danger of frost has passed. Mandevillas grow well in containers, and this is convenient if you plan to overwinter it indoors. I have not had any trouble carrying plants over the winter, but because I don’t have a greenhouse, my plants survive in a state of semi-dormancy. It takes some time for them to return to bloom when I move them outdoors. If you are an impatient gardener like me, you may end up purchasing a new blooming plant each year anyway.


Photo credits: Moonflower by Rita Pelczar; Mandevilla by David Cavagnaro

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