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Gardening: Mandevilla is a colorful summer and fall bloomer

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Gardening

Mandevilla Rio Red is a prolific bloomer from spring to late fall. The large star-shaped flowers are a deep carmine red. Anthony Keinath/Provided

Stores already are filled with pots and hanging baskets filled with colorful mandevilla cultivar Rio. This dwarf mandevilla has transformed an obscure sprawling vine into a popular compact perennial.

Naming mandevilla

The official common name for mandevilla is rock trumpet, which comes from the large funnel- or trumpet-shaped flowers. The horticultural trade calls the plant “mandevilla,” the same as the botanical name Mandevilla. The older botanical name Dipladenia still shows up in some references, but today, all Dipladenia are considered to be Mandevilla.

Rio, the first dwarf mandevilla, is one of many hybrids created by crossing different species of the plant. It is also described as a mounding cultivar because its branches are only 12 to 18 inches long, whereas vining cultivars can grow 10 to 15 feet long.

Several other cultivars are available, but I won’t mention them here, as the cultivars available in a local area change regularly.

The typical colors are red, pink and white. A wider color selection is available in Europe, so we may soon see several shades of pink and red.

Growing mandevilla

Gardening

Pink mandevilla mixed with black-eyed Susan vine, callibrachoa and verbena in a wall sconce planter. Anthony Keinath/Provided

Most mandevilla in South Carolina are grown in containers because they are tender, tropical perennials native to South America. I haven’t tried one in the ground yet. Mandevilla are susceptible to Phytophthora root rot and blight, so keeping the plant in a pot is the easiest way to avoid this deadly disease.

Mandevilla neds full sun, at least 6 hours a day, to set flower buds. It will flower, though not as profusely, with 4 to 6 hours of sun.

Some references, such as the list of Texas Superstar plants, recommend light afternoon shade for mandevilla. I haven’t found that to be necessary in the Charleston area, where summer afternoons tend to be partially sunny.

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Rio will lose its compact form if it gets less than 4 hours of sun. The vines will lengthen, and the leaves will be farther apart. This stretching is a sign the plant isn’t getting enough sun, and it should be moved. Elongated vines can be pruned (after the plant is moved to a sunnier spot) to keep them short.

Rio has an impressively long blooming time. Last year, my plant bloomed regularly from spring 2019 until early February 2020, a remarkably long time. As late as November, it had 19 flowers and 29 buds.

Mandevilla prefers normal to moist potting soil. If the soil dries out, leaves will turn yellow and drop. Plants in pots should be watered when the surface of the potting soil is dry.

Mandevilla needs regular fertilizing, about once per month from March until it stops blooming in the fall. The fertilizer should be one recommended for blooming plants.

In the greenhouse, mandevilla can be bothered by spider mites, aphids and whiteflies. I haven’t seen any of these pests on my plant (yet).

Mandevilla is browsed by deer that eat the buds and shoot tips. Gardeners in areas with deer can grow dwarf cultivars in hanging baskets. This plant is not included on the ASPCA list of plants poisonous to cats, dogs or horses.

Keeping mandevilla

I’ve had my Rio Red plant for almost two years. It’s carried into the garage when temperatures are predicted to fall to 35 degrees. (There’s always a bit of uncertainty in how low the actual temperature will be.) This spring I pruned my plant to remove some of the older stems.

One attractive feature of Rio is that it branches well, and the new branches fill in bare spots on its stems. New branches also appear from the base of the plant.

Mandevilla is an excellent choice for summer containers because it is easy to grow and blooms prolifically.

Anthony Keinath is professor of plant pathology at the Clemson Coastal Research & Education Center in Charleston. His expertise is in diseases of vegetables. He is also an avid gardener. Contact him at tknth@clemson.edu.

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