How to grow mandevillas

What are mandevillas?

Mandevillas are vigorous climbers from tropical woodlands in Central and South America. In summer, they produce showy trumpet-shaped flowers set against glossy, evergreen leaves. The flowers can be red, pink, white or yellow, depending on the species, and are often produced in large clusters. Although spectacular, mandevillas can be challenging to grow long-term as houseplants, as they need specific growing conditions and can get quite large over time. Some newer cultivars have been bred to be less vigorous and better suited as houseplants.

Mandevillas need warm, humid air and plenty of bright, indirect light, along with sufficient space and a large sturdy support to climb up. They can be moved outside for a few months in summer, to a warm, sheltered patio or doorstep, in sun or light shade.

Mandevillas produce large trumpet flowers in summer

Choosing mandevillas

There are several species and cultivars of mandevilla, four of which have been given an RHS Award of Garden Merit, as they performed well in trials, so make reliable choices:

• Mandevilla boliviensis AGM – white flowers with a yellow centre

• M. splendens AGM – large rose-pink trumpets up to 10cm (4in) across 

• M. × amabilis ‘Alice du Pont’ AGM – clusters of up to 20 bright pink flowers

• M. laxa AGM – large, jasmine-like white or cream flowers that are richly fragrant 

Buying mandevillas

Mandevillas are not widely available, but you may find them in larger garden centres in summer, when in flower, and online from specialist houseplant or tropical plant suppliers. They are often still sold under their former botanical name, Dipladenia.

For details of stockists, go to RHS Find a Plant and search for ‘mandevilla’. 

Mandevillas can usually be kept in their original pot for the first few years, until the roots become overcrowded. They should then be repotted in February or early March:

• Choose a new container that is only slightly larger, as overpotting may reduce flowering. They generally do best in a large container, 25–30cm (10–12in) wide

• Use a peat-free loam-based compost, such as John Innes No 3, with added grit to improve drainage

• Position the plant in its new container at the same level it was previously growing. Firm down the compost, then water thoroughly to settle the compost

Location

Mandevillas can be grown as houseplants in a bright room or warm conservatory, as long as they have plenty of space. They can also be grown in a heated greenhouse. Provide support for the climbing stems, such as a tripod of tall canes in the container, or a wooden trellis or system of wires fixed to a wall.

They need bright but indirect or filtered light. Make sure there is shade from hot sun in summer, as this can scorch the leaves.

Temperature

From spring to autumn, provide at least 21°C (70°F) by day and 18°C (65°F) by night. Warmth in spring encourages new flowering stems to form, while in autumn it can help to extend the flowering period.

Over winter, plants need cooler temperatures and reduced watering. But ideally they should still be kept above 15°C (60°F) at night. Some may survive if kept slightly cooler, above 10°C (50°F), and a few, such as Mandevilla laxa, may cope down to 5°C (41°F). Plants may drop their leaves if kept too cool. 

Mandevillas can be moved outdoors for a few months in summer, but only in very warm, sheltered gardens. Acclimatise them gradually to outdoor conditions by hardening off. They need daytime temperatures above 21°C (70°F) to maintain flowering. Bring them back indoors before temperatures fall below 10–15°C (50–60°F) at night.

Watering 

• Water mandevillas regularly throughout the growing season, from spring to autumn. Keep the compost moist but not waterlogged

• You may need to water daily in hot weather, as containers can dry out quickly. It’s best to water early in the morning or in the evening, when temperatures are lower

• ​In winter, it’s important to reduce watering, keeping the compost slightly damp. But don’t let it dry out completely

Humidity 

These tropical plants like humid air, so mist the leaves daily in summer. You could also stand the container in a tray of damp gravel, but make sure the compost doesn’t become waterlogged.

For more tips on raising humidity, see our quick video guide:

Feeding

From spring to autumn, apply a general-purpose liquid fertiliser monthly, as the compost won’t provide sufficient nutrients to fuel this plant’s vigorous growth. 

To encourage flowering, you can change to a potassium-rich feed, such as tomato fertiliser, in summer. Follow the dosage instructions on the packet. 

Mandevillas need initial pruning so they develop into well-shaped plants, then subsequent light pruning annually, to keep them at a manageable size and promote flowering. Wear gloves when pruning, as the milky sap can irritate skin. The stems may also need initial training onto their supports.

Pruning and training new plants

New plants should be pruned in spring, to create a well-balanced framework of woody stems:

• Select three to five strong, young shoots, and prune out any others

• If there is only one main stem, reduce its length by one-third to encourage new stems to sprout from the base

Mandevillas climb with twining stems and need sturdy support to carry their weight. They are often sold growing on a small support, but this may not be large enough in the long term – it’s usually best to replace it at the outset. Suitable supports include wooden trellis or a system of wires fixed to a wall, or a large tripod of tall canes inserted into the container. The latter gives you more flexibility to move the container, perhaps placing it outside in summer. Tie the main stems to the support initially, to create a well-spaced framework and encourage the stems to start climbing.

Annual pruning

Established mandevillas can grow quite large (3m/10ft or more over time), so annual pruning helps to keep them to a more manageable size. It can also encourage flowering. In late winter or early spring:

• Prune out any overcrowded or weak shoots

• Shorten side-shoots to within three or four buds of their permanent framework, to encourage new flowering shoots to form

You can make new plants by:

• sowing seeds in spring – place in a heated propagator at 18–23°C (64–73°F)

• taking softwood cuttings in early summer – to encourage rooting, place in a heated propagator at 20–25°C (68–77°F). Wear gloves when taking cuttings, as the sap can be a skin irritant

Mandevillas are tropical plants and require suitably warm, humid conditions, along with regular watering and feeding in spring and summer, to flower and grow successfully. Plants may fail to flower or drop their leaves when their needs aren’t met. See Planting and Ongoing Care, above, for full details.
 
Failure to flower is often caused by temperatures being too low, especially in spring. Mandevillas bloom on the current year’s growth, so they need warmth in spring to encourage the production of plenty of new flowering shoots. Provide a daytime temperature of 21°C (70°F) and a night temperature of 18°C (65°F).
 
Check plants regularly for insects, including:

• mealybugs 

• red spider mites, which cause the leaves to appear speckled or bleached

• glasshouse whitefly