I keep my tropical w.lilies in a 700 gal. pond in the g'house . I usally use a 800 watt titamium(sp?)
aqua. heater in the pond to keep the lilies alive & several of them will keep blooming all winter. this year I got a 500 watt(titu) heater & it's doing the job too...a few lilies are still blooming .
I also put plastic over the pond( held up by pvc pipe) to help keep the heat from riseing up into the air . I've been doing it for 3 years now & it works for me .
bonnie
I overwinter 30 tropical w.lilies & am able to keep water hyacinth's for next year....I start out with 3 hyacinth's & ended up with over 50 last Spring...