Dipladenia is a tender, evergreen vine from the periwinkle family, which bears clusters of white, rose, crimson, pink or purple trumpet-shaped flowers in the summer months, although one species has salmon-pink flowers which bloom throughout the year. The colourful plant adds beauty to your home indoors or out, but does require special care.
There is some confusion as to whether this plant should be called Dipladenia or Mandevilla, but most growers use the name Dipladenia to differentiate this more bush-like plant from its cousin, the Mandevilla. It has moderately vigorous vines that do well on a trellis or in a hanging basket. It is attractive to bees, butterflies and birds. Unfortunately, it is also a target for aphids, spider mites and scale. If you see any evidence of harmful insects, you can try washing them off with a stiff spray from a hose. If they persist, try a little neem oil on the leaves. Note that parts of the plant are poisonous if ingested, so keep the plant away from children and pets.
Keep the soil evenly moist during the spring and summer growing season, but allow it to dry between waterings during the dormant seasons of autumn and winter. Use warm water and make sure the pot has a drainage hole with pebbles or gravel in a dish underneath to hold in the water and humidity (being sure the pot is sitting on gravel and not in the water). It is also important to mist the plant regularly, particularly while it is in bud and flowering.
Dipladenia does well in sun to partial shade but must have bright indirect light and not direct sun. A good indoor location is a curtain-filtered window. In warmer climates, the plant can be grown outdoors, but in colder climates, it is best treated as a houseplant. The optimal temperatures for dipladenia are 15C to 18C at night and 20C to 30C during the day. Dipladenias are sensitive to frost, so cover and mulch outdoor plants or move containers onto a porch when frost threatens.
The best soil for a Dipladenia is two parts peat moss, one part packaged potting mix or loam, and one part sharp sand or perlite, with a small amount of crushed charcoal. You should fertilise the plant every two weeks during the growing season with a fertiliser high in phosphorous like 10-20-10. As an alternative, you can use a granular slow release fertiliser if applied annually in the early spring. Avoid using fertiliser in the winter.
Dipladenia grows into a bushy shape but without pruning, it will act vinelike, growing 1.5 to 2 metres high. To keep the plant bushy, pinch out the growing tips every now and then; to encourage growth, prune in the fall. To propagate new plants, take young shoots in March and dip them in rooting hormone. Insert the shoots in a pot of moist sand or perlite and peat moss, making sure to provide bottom heat. Keep the shoots in a humid environment by placing the pot in clear plastic in indirect sunlight or under a fluorescent light. Once rooted, you can move the shoots in 8 cm pots initially and then to larger pots later when needed.