Answer: It doesn't sound as though your mandevilla is very happy. 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.
Your plant will need a rest when summer is over. 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.
The tiny green bugs may be aphids and you can control them with Insecticidal Soap (apply according to label directions). Since these pests have sucking mouthparts, they feed on the fluid within the tissues of your plant, leaving yellow spots. Once you control the infestation, the leaves won't develop yellow spots.
Best wishes with your mandevilla!
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