Sigh, can't get caladiums to grow here. I hear you about nasturtiums and containers! Although if the container is BIG enough.....heh heh, I have one that would qualify as a raised bed and the nasturtiums did just fine in it....just about took over! Nice looking combinations there.
Confidence is that feeling you have right before you do something really stupid.
Here is my amature opinion about nasties in containers. 20 inches and smaller. The soil gets too hot and retards growth.
Bigger than 20 inches and planted in the middle they would probably work because its cooler.