I'm not in your zone but I would think once frost danger has passed it would be ok. Try putting them in the shade first. That's what works for me. I've had mine out since around Easter but they didn't like going in the sun. I had to move them to a shadier spot and gradually move them around to full sun. They are doing great now.

I live in Texas and I cant say I have to bring in any of my water plants at all for the winter. I havent anyway and so far everything has done just fine. Taro included. Some die back but the tubers etc stay just fine and well protected in the water and my plants that do die back in the winter come back full and wonderful every year. Im not moving my water plants in and out every year .... That is too much work for me. You probably get a much harsher winter than I would.

Both of these like really tropical temps so I generally wait until night temps stay above sixty degrees to prevent a setback to growth. Here in GA Zone 8 both are root-hardy outside but I always bring a pot of each inside to enjoy during winter. They adjust fine to outside after temps get steadily and reliably warm. josh