The plants of dipladenia or mandevilla are creepers of South American origin, evergreens; the botanical name of the genus is mandevilla, but they are also commonly called dipladenie (another name of the genus, synonym of mandevilla); once in Europe they were cultivated only as indoor plants, except that in the apartment the conditions of brightness brought the plants to produce almost exclusively lush foliage, and very few flowers; it was only towards the end of the 1900s that the potential of this plant as a garden flower was fully understood.
In recent years the dipladenia have acquired a great success as terrace plants, thanks to the fact that, if grown outside, they tend to have a long flowering season, from April to May until the first cold of autumn. In the nursery you can find many hybrids, even with leaf or variegated flower; in particular, very sun-resistant hybrids have been produced, whose trade name is sundavilla. Generally in the nursery we find mainly dipladenias of the splendens species, with oval, pointed leaves, with a smooth page, quite small; recently some plants belonging to other species are spreading, with larger and wrinkled foliage. The flowers are the same for all species, trumpet-shaped, of intense color, in shades of pink and red; the larger leafed species often have flowers with contrasting throats.
The mandevillas are evergreen climbing plants, which are grown in the garden or on the terrace, making their twining branches climb, or letting them fall back or remain prostrate, developing as ground cover plants. They prefer very bright positions, both in full sun and in partial shade; the success of these plants came initially mainly for the terraces placed in partial shade, where other plants tend to bloom in an unsatisfactory way.
They don't fear the summer heat, but they fear the frost, especially if intense and prolonged; therefore they are cultivated in full ground only in areas with a mild winter climate. In the rest of Italy the dipladenie during the winter must be placed in areas sheltered from wind and frost, or leaning against the house and covered with non-woven fabric, which prevents frost from reaching the roots. To have an abundant flowering, the dipladenie need to have a period of vegetative rest during the winter; for this reason it is completely counterproductive to move the house plants during the coldest months; if desired however it is possible to shelter the vessels in a cold greenhouse, or in an unheated stairwell, with maximum temperatures no higher than 12-15 ° C.
To have a plant that is always lush and compact, at the end of flowering, in autumn, shrubs are pruned about 8-10 cm from the ground; in spring we will stimulate the plant to produce new compact branches. They need regular watering, to be provided only when the soil is dry; they fear water stagnation and endure even long periods of drought without problems; watering is provided only from March to April until the cold of autumn; during the cold months we avoid watering. In the vegetative period it is good to supply a fertilizer, to be mixed with the water of the watering, every 12-15 days.
The Dipladenie spread easily by seed, it is more difficult to find the seeds, because although these plants bloom profusely throughout the summer, they do not always produce seeds; if you see a pod on your dipladenia, wait for it to dry on the plant, then remove the seeds, and place them on the surface of a seeding tray, filled with peat soil mixed with sand; the germination soil must be kept humid and the tray must be kept in a bright area, but not directly affected by sunlight, which could completely dry the substrate, and in this way delay seed germination.
To stimulate the seeds to germinate, before placing them on the ground, it is also possible to leave them in water for about 12 hours, in this way germination will take place more quickly. The young seedlings should be grown in the apartment during the winter, possibly in an area that is not very heated and very bright.
Dipladenia or Mandevilla: Tips for multiplication
To obtain mandevilla plants more quickly, you can use the propagation by cuttings; in spring or summer we take apical branches, cutting them from those branches that have not produced flowers; from each sprig we get portions about 7-10 cm long, to which we will raise the lower leaves. The upper leaves should be cut in half, then we insert the twig in the rooting hormone, and then in a jar, full of soil and sand; even the jars with cuttings should be kept in a semi-shaded area, but very bright, and the soil should be watered regularly, avoiding it to dry completely.
To better maintain the moisture of the seeds and cuttings, especially in the first weeks after having placed them in the ground, an effective device is often used: the jars and the seeding tray are placed in a transparent plastic bag, for example a common frozen bag. In this way the plastic will keep the humidity always high and the climate always humid and warm, just like the plants that need to germinate; after the seeds have all sprouted and the cuttings have begun to produce new leaflets, we can remove the jars from the bag, and place them anyway in an area sheltered from the wind.