Three different mandevillas sharing the same pot. Photo: http://www.madisongardensnursery.com
The mandevilla (Mandevilla spp.) has emerged from decades of relative obscurity to become a popular patio plant for summer decoration. And increasingly, gardeners want to know if they can somehow save it from the cold to grow it again another year. The short answer is yes, they can, but getting to know any plant helps it to grow it better, so…
The genus Mandevilla is native to tropical and subtropical areas of the New World where it grows as a vine. It’s in the dogbane family (Apocynaceae) and typically has trumpet-shaped flowers in shades of red, pink or white, rarely yellow. Some hybrids are bicolored or have double flowers. There are over 175 species in the genus, but the most common ones grown in home gardens these days are hybrids, often sold as M × amabilis.
The species now considered mandevillas were once divided into two genera, Mandevilla, with larger flowers and a more distinctly climbing habit, and Dipladenia, with smaller flowers and a shrubbier habit. However, they’ve all been reclassified into the genus Mandevilla and if you’re still calling your plants dipladenia, you really should change.
The genus is named for Henry Mandeville (1773-1861), a British diplomat with a passion for tropical plants
Mandevillas love sun and warm to hot temperatures, so it’s not surprising they do so well outdoors in the summer months. However, they are not frost tolerant, so if you don’t bring them indoors for the winter, they won’t survive except in very mild climates (USDA zones 9 to 11).
Grow Them as Houseplants
The simplest way of keeping mandevillas alive indoors is to bring them indoors while temperatures are still warm and to treat them as houseplants.
Read Bring Houseplants Indoors Without the Bugs to learn how to bring them without bringing in insect pests too.
Put your mandevillas near a sunny window or under lights and water them regularly, as soon as the potting soil starts to feel dry to the touch. Offer them high humidity, if possible, to reduce leaf drop. They’ll probably bloom some indoors, but due to the shortening days of autumn and thus decreased sunlight, not nearly as much as outdoors.
Don’t hesitate to prune them back somewhat when you bring them in for the winter, nor in fact, to cut back wandering stems at any season. However, for best bloom, leave the year’s main pruning—when you can cut them back severely, say to a foot (30 cm) or so from the ground (stems become woody and less floriferous over time)—, until early March. That way, new growth will appear under the most intense light possible, leading to more abundant summer bloom.
To avoid stimulating long, weak stems, avoid fertilizing in fall and winter. Start again in spring and continue through the summer. Any all-purpose fertilizer would be quite acceptable.
Normal indoor temperatures are fine and mandevillas, like humans, seem to do best when the temperature drops bit at night.
Or Put Them Into Dormancy
This is method is riskier, but if you have a cool spot indoors, you can try forcing your mandevillas into dormancy.
In this case, leave them outdoors until nights start to drop to about 50˚F (10˚C), as this will slow down their growth. Then prune severely, down to about 1 foot (30 cm) and bring the plants indoors. If you don’t prune, there’ll be a lot of leaf drop and mess: consider yourself forewarned!
Place the dormant plants in a cool but frost-free spot, such as a root cellar or a slightly heated garage. Water lightly, only about once a month, just enough to keep the soil from drying out completely. In early March, move the plant back into the sun and start watering and fertilizing regularly again as it starts to recuperate.
Back Out for the Summer
No matter how you overwinter your mandevillas, when night temperatures outdoors start to rise faithfully above 60˚F (15˚C), it’s time to reacclimate the plants to outdoor conditions and enjoy another season of outdoor bloom. This is also an excellent time of year to repot them.
Do watch out for mealybugs and scale insects: they often seem to surge out of nowhere in late winter or early spring. Aphids too are an occasional problem. Repeated sprays with a solution of insecticidal soap will help control them. Otherwise, mandevillas have few pests.
Mandevillas are poisonous: do keep them out of reach of children and pets.
Mandevillas: indoors or out, they’re truly beautiful plants.