My new Dipladenia plant just lost half of its leaves. It is near a very sunny window. What could be the problem?

Question

Only a few leaves had turned yellow. All others looked perfectly fine.

Answer 1

Since you say it's new, I imagine it is the change of environment. Here is more information:

https://www.gardeningknowhow.com/houseplants/hpgen/houseplant-dropping-leaves.htm

https://www.gardeningknowhow.com/ornamental/vines/mandevilla/growing-a-dipladenia.htm

https://www.gardeningknowhow.com/plant-problems/environmental/plant-leaves-turn-yellow.htm