Is there a plant that would be happy here?

[Lisak1]

Maybe it was still too cold?

Last month? Maybe. It does prefer cooler weather but not freezing temps. It also likes moving water. And yes, I watch for it around this time and always find it for a buck a bunch. Best dollar I spend all year! We grow bushels of watercress in our pond!

 

[bettasngoldfish]

The stuff I got from Trickers the last few years has always done well for me. So much so that I have to thin it out or it blocks the water flow.

The stuff from Giant Eagle looked much more tender than the ones I bought from Trickers.

 

[tbendl]

I like the iris suggestion and I agree with everyone else that you did a fantastic job on your waterfall. I bet it sounds heavenly!