Answer: Dipladenia splendens is also called Mandevilla sanderi. If your plant suddenly lost its leaves, the cultural conditions are not quite right for it. You may have over or under watered it, or it may have suffered fertilizer burn from over application.
Indoors, mandevillas need curtain-filtered or bright indirect sunlight. Provide night temperatures of 60 to 65F and day temperatures above 70F. Plant in a mixture of equal parts peat moss, potting mix and builder?s sand. In spring and summer, feed every two weeks with a fertilizer high in phosphorus such as 10-20-10.
Outdoors, grow mandevillas in partial shade. They need rich, well-drained, sandy soil with humus added. Provide a frame, trellis or stake for support. Pinch young plants to induce bushiness.
Since 45 to 50F is the minimum temperature that can be tolerated by mandevilla, plants should be moved indoors for the winter if your garden usually receives frost. Before bringing them indoors, examine them carefully for pests. Look under the leaves, in the leaf axils, and in every conceivable nook and cranny for insects and their eggs. Remove any diseased or dead leaves by hand. Insect-infested plants can be doused with a forceful spray of water to dislodge the pests, or you can use insecticidal soaps or other appropriate insecticides labelled for use on your plant. You may have to prune some of the plant to compensate for any root loss.
Move the plants to a lighted location where the temperature is above 45 to 50F. Reduce the frequency of watering to coincide with the plants? rest periods induced by the cooler temperatures and reduced light.
In late winter or early spring before growth begins, prune by removing old, crowded stems and shortening others. Even if mandevilla is pruned almost to the ground, it will bloom the same summer on the new shoots, which develop from the base of the plants.
Hope this information helps you determine just what may have caused the symptoms in your plant.
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