I worked on the theory that they were aquatic plants that were going to become glasshouse pot plants so I grew them in black magic potting mix and kept the roots wet. I grew just about every type of Echinodorus available and a lot of the "more aquatic" stem plants such as Rotala and Heteranthera. I stayed away from most of the very large Echinodorus sp.and the stem plants that were not easy to convert to submersed growth. Just grow them like pot plants and the hassle goes away. There are a few that need high humidity such as Java ferns and Anubius, also the true aquatics such as twisted val, ambulia and cabomba. The only plant I am growing at the moment is Cardamine lyrata which I have in a terrarium with newts and growing very well with light from a cool white energy saver bulb.