Anne, I missed this thread last week but have a little thing to add - I have planted a dwarf Lotus called "Baby Doll" in a 20gal. tub this year. (got it from Texas Water Lilies, too!) I grew it once before in my pond, but it didn't get enough sun to bloom for more than about a month. In the tub, I can move it around the yard so that it can be in the sun all summer and into fall.
For the winter, I'll move it back to my most protected, sunny spot and the tub of water will act as a nice big, dark heat sink for my roll-up tent that I put over my veggies and tender plants when we get cold nights. It will stay warm enough through the winter for the lotus plant to survive, too.
Just thought I'd mention this because a similar tub could act as a heat sink in your greenhouse in winter, too. I know a couple of people who have grown small lotus in a half-barrel size tub of water.
I agree about the growing water flowers in a glass - they like some soil and a fair amount of fert as well as lots of sun to bloom.
Here's my new tub - the forks are to keep the raccoon from stepping in the pot and upsetting it. Once the plant gets more mature, the leaves stand up out of the water, and so do the flowers. I just planted this a month ago.
