Why Doesn’t My Mandevilla Flower

Question

It is in large pot. It’s several years old. Straight stems, and second year it hasn’t blossomed.

Answer 1

Is it in a sunny location? Do you prune it back in spring? If so, have you changed out the soil recently? Container soil eventually breaks down and loses its substance and fertility. If it is too large to easily replace the soil, just work fresh soil in at the top.

Here is more:

https://www.gardeningknowhow.com/ornamental/vines/mandevilla/getting-mandevilla-to-bloom.htm