Jane Weber Main

Jane Weber

JANE'S GARDEN

Mandevilla is a genus of about 200 species of flowering vines that evolved in tropical and subtropical America. No part of continental U.S. is within tropical latitudes. Mandevillas are suitable for frost-free climates in cold zones 9a–12. Further north, a hard freeze will kill top growth to the ground and perhaps freeze the roots to death. These plants can be treated as annuals and replaced every spring, or be grown as container plants to be brought indoors during winter.

First described as a genus in 1840, the name honors Henry Mandeville (1773–1861), a British diplomat and gardener. Mandevilla belongs to the dogbane family, Apocynaceae. Those with smaller flowers and more compact growth habit were formerly and mistakenly called dipladenia but are now correctly identified as mandevillas

Fast-growing, twining, woody-stemmed mandevillas need support. Stems of large varieties, including ‘Red Velvet,’ can reach about 20 feet long and rapidly cover a trellis, arbor or pergola in a single growing season. Cultivated varieties, selected and manipulated by human plant breeders, are bred and cloned to remain more compact, so are better choices for covering mailboxes, trellises and lampposts. Smaller cultivars are suitable for hanging baskets and containers. The more compact cultivars like Sun Parasol ‘Burgundy’ may have meter-long stems.

Many mandevilla species originated in the Serra dos Órgãos National Park rainforests, in the mountains an hour’s drive from Rio de Janeiro in southeastern Brazil. Climate in this national park is “tropical superhumid” with 80% to 90% relative humidity. The park, in the Atlantic Forest biome, is also one of the few natural habitats of about six to nine species of Schlumbergera, which are not true cacti nor do they bloom naturally at Thanksgiving, Christmas or Easter. Use of former incorrect common names is dying out as science, technology, global communication and politically correct younger generations of gardeners, techies and botanists demand accuracy.

Plant Mandevilla in full sun of at least six hours a day. The soil should be humus-rich, moist and must be well-drained to prevent root rot. While mandevilla tolerates summer heat, leaves can sunburn without some shade in the middle of the day. Fertilize seasonally — yellowing leaves may indicate nutrient deficiency. Flowering season spans the summer in subtropical Central and South Florida. Trumpet-shaped flowers can be 4 inches in diameter and 2 inches long. Smaller compact varieties have smaller flowers. Individual flowers last several days.

The named, cross-bred cultivar Mandevilla x amabilis ‘Alice Dupont’ has large pink flowers. It is named after the wife of the founder of Longwood Gardens, Penn. Other varieties have red, pink, creamy and striped flowers. Mandevilla boliviensis has white flowers with yellow throats and will grow in the U.S. in cold zones 10–11. Some yellow flowering vines still mistakenly marketed as yellow mandevilla, yellow dipladenia and wild allamanda actually may be Urichtes lutea or Pentilinon luteum and are closely related to Mandevillas.

Mandevilla splendens, native to Brazil, is hardy in USDA zones 10 through 11. It was formerly identified as a dipladenia and was one of the parents of the ‘Alice DuPont’ hybrid.

Scale and mealybugs occasionally pester Mandevillas. Control insects with insecticidal soap.

Tip prune to induce branching, bushiness and more flowering. The milky sap in dogbanes contains irritating glycosides which can cause skin irritation, itching and rashes. Take precautions as all parts of all dogbane plants — including Mandevilla, Nerium (Oleander), Trachelospermum and Catharanthus — contain cardenolide glycosides, which are poisonous and heart-arresting if ingested in large amounts. Modern medicine and research indicates some beneficial and therapeutic uses for cardenolide glycosides

For further reading, check the University of Florida at https://tinyurl.com/yywkc4h3, and UF/IFAS publications at https://tinyurl.com/y6cmbp85. For breeder information, see https://tinyurl.com/y68e7xqs.

Jane Weber is a professional gardener and consultant. Semi-retired, she grows thousands of native plants. Visitors are welcome to her Dunnellon, Marion County, garden. Contact her at jweber12385@gmail.com or phone 352-249-6899.

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