I cut back my potted mandevilla a month ago. The new stems are so weak and lean over. How do I make them become strong?
Pruning a Potted Mandevilla
Certified GKH Gardening Expert
This will usually happen with a lack of light. Are they also very light in color? This will further indicate that it is lacking light.
It is naturally a vine, so it will lay over without support, but if it is too weak then fixing the lighting will take care of that.
This article will give you information on the care of these: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/