Q.Mandevilla Plant
I saved my Mandeville vine from last year. I had it kept in a 5″ clay pot and it did fine. This spring I put it in a 24″ pot, put it outside. It seems to be doing well. I know that mandeville vines are fast growing, but this plant isn’t living up to its expectations. There is only about 12″ of growth. It receives about 5 hours of sun and the rest in partial shade. Was the 24″ pot to big? Does the vine grow better when it is somewhat root-bound?

Certified GKH Gardening Expert
Generally, when you pot up, it should only be an inch or two larger of a container. My guess is that much of the soil remains too wet, since there are no roots through it to pull out more of the water. This can cause slow growth.
Fertilization is important as well, but only if the plant needs it. A soil test will confirm this.
Here is an article that will help you with their care in container:
https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm
These articles will help you with soil testing:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm