can I plant white mandevillas in large pots but need them to flow down – would I need to put some sort of staking around pots.
prefer mandevillas to diplidenaeas
Certified GKH Gardening Expert
In short, trailing plants don't like to climb and climbing plants don't like to trail. You can, certainly, grow them in container, but you will want to be looking to let them climb onto something. They will naturally attempt to hold themselves upward and fight the trailing nature.
This article will help: https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-plant.htm