I am still waiting on my dwarf perrybaby to ship. I don't think spring is ever going to get here.you can safely put out hardy water lily's and hardy plants but wait on the tropical floaters like water lettuce.
My water lily had new pads that were almost touching the surface of the water until winter came back and that pond froze and now has ice again....
That plant will be ok but those new water lily pads might have froze and plant may have to grow new ones again...
I am not really worried about the duck weed. I got it from a friend for free as a treat for the fish. Food is something my tubby little finned fiends don't lack.