Mandevilla
For bold, unmissable flowers that love the heat, look no further than these climbing beauties. Despite some confusion about their name, they provide fuss-free colour in most gardens, writes STEVE FALCIONI
Mandevillas are a group of woody climbers and small shrubs that originate mostly from Central America and South America. There are about 170 different species, and it’s the climbers and semi-climbers, with their large, trumpet-shaped flowers ranging mainly from white to pinks and dark reds, that have become popular in Australia.
Broadly speaking, there are two groups of mandevillas: those with smooth leaves and those that have crinkled leaves. The smooth-leaf types are semi-climbers or small bushes. These originally belonged to the genus Dipladenia, but were reclassified as Mandevilla by American botanist Robert E Woodson in 1933. Still called dipladenias by many gardeners, the smooth-leaf types available at garden centres are mostly hybrids of M. sanderi or M. splendens.
The members of the group that produce larger, crinkled leaves are more vigorous climbers, and these have always been known as mandevillas. It can seem a bit confusing trying to remember what’s what, but if you refer to the plant label for the plant’s size, you can’t go wrong.
Despite their differences, all mandevillas prefer the same growing conditions, and when you give them what they like, you’ll be rewarded with months and months of beautiful flowers.
getting started
Although these are warm-climate plants, they are surprisingly tough and will grow in regions with cool winters, as long as you provide them with frost protection. When the temperature dips below 10°C, many become semi-deciduous or fully deciduous, so expect them to look sad through a cold winter.
Mandevillas grow well in full sun to semi-shade. In regions with very hot, dry summers, give them a little protection from the fierce midday and afternoon sun. They can handle a range of soil types, but prefer one that is rich in organic matter.
Poor soil results in less growth and fewer flowers, so do what you can to improve yours. The soil must be free-draining, and this is non-negotiable, as prolonged wet soil can cause the roots to rot.
Mandevillas aren’t especially hungry plants. They are happy with a handful of organic fertiliser pellets every 2–3 months from spring to autumn. If you have poor soil or are trying to establish young plants, supplement this with an application of organic liquid fertiliser every 2–4 weeks.
Generally, mandevillas don’t require much pruning. The small-bush types sometimes throw out whippy growth, which can be tip-pruned to keep the plant dense. If either the bush or climbing types become a bit sparse, prune them harder in early spring, and the warmer weather will encourage a stack of new growth. Wear gloves when pruning, as their white sap can be a skin irritant.
These plants are generally pest free, but they can be attacked by aphids, scale and mealy bugs. In dryer regions, spider mite and whitefly may also cause some damage. Spray pests with a botanical oil or neem product for organic control.
container culture
Mandevillas are a good choice for pots, as their roots develop water-storing tubers that help them handle periods of drying out from infrequent watering.
The compact, smooth-leaf types are the best choice for containers. I’ve had long-term success growing these in 25cm pots or larger. The more vigorous crinkle-leaf climbers don’t do as well with their root ball restricted, but if you’d like to grow one in a large pot and are prepared to pamper it, it’s worth a try.