I haven't grown sandersonia, but I have grown colocasia. They like A LOT of water, they can even be grown in ponds (where I grew mine). They need to be dug/overwintered in zone 6 or lower, and you might be touch-n-go in zone 7, but zone 8 you should be fine leaving them in the ground over the winter. They can get quite large (5-6ft tall, w/2ft leaves), so space may also be a consideration and their big leaves can be ripped up by harsh winds, so you may want to site them with some wind protection. They are stunning though, and you will get a lot of comments/compliments from it!

--Bob