Hello .. I have a few ponds with fish in Oregon zone 6b for over 25 years. I can suggest hardy water lilies, hardy water iris, winter mint, lizards tail, arrowhead plant and marsh marigold. There are much more These all over winter in the pond good to zones 3-4.
Much of the water cover plants like pickerel, taro, cardinal flower and water lettuce I plant after the water temps are maintained at 60 degrees. Most of the cold hardy plants are available now at nurseries and the non hardy plants like taro mosaic plant will be available after may or generally after the temps are warmer.
Every plant in the pond needs to have a purpose – whether it is color or height, or to deter algae growth. Using a variety of water plants can add visual interest as well as keep your water garden healthy. If they are hardy plants are so easy. Perennial water plants can also save you money in the long run. Visit some of the many pond plant online available for ponds. Get what you can now keep inside while temps warm up then you 'll have exactly what you need.
