I put mine in a pot and sunk pot and all into the ground. I believe Mandavilla is a tropical or subtropical, so you will have to bring it in for the winter.

I live in NC and a neighbors mandavilla did not live thru last winter. I don't know if she provided a heavy mulch or not though.

I plant mine in a bigger planter for the summer, along with other flowers. It really just holds its own and really doesn't grow much until the weather is consistently warmer.

Not sure what the nursery person meant by pruning. I know some people trim their plants annually in spring to encourage new growth and in theory blooms.

Last fall I dug my mandevilla out of the big planter and put in a smaller pot which I brought indoors for the winter on a bright windowsill. I had to trim a bit as it was tangled somewhat. By the way, in relation to the size of the plant it really didn't have an overly huge root system, which made it easier to fit in a smaller pot.

Then, when it went outside this spring it really looked terrible and lost a lot of leaves. The ones that were left were sort of rusted with blotches. Suddenly, when the warm weather finally arrive, it's starting to sprout new normal looking growth.

Glen