The Water Hyacinth (Eichhornia crassipes major) is the most common of floating oxygenators you’ll find for sale and while you may buy a few in the spring, you’ll have hundreds by the fall.
In the full sun, this is a fast growing plant able to leap tall buildings in a single bound. In anything less than full sun, the plant survives (it may stretch into bullet shapes rather than ball shapes with less sunlight) but it doesn’t grow well.
It does require full sun to flower and even then, in the north, the flowering will not be extensive. (enough to tantalize) If you get a bloom, enjoy it as each individual blossom will only last one to two days.
Where to Grow
It grows best for me in still water although it does well if placed in the top of the pond bio-filters.
Water Hyacinth and Fish
The long dangling roots are appreciated by fish and a few koi will keep them well pruned. If too many fish are in the pond, these water hyacinth will be left without roots.
Interestingly enough, this floating oxygenators roots are almost perfectly formed to support fish egg survival and hatchling success.
If left long, the roots help produce huge plants and absorb pond nutrients (thus reducing the nutrients available for algae growth).
The water hyacinth is a tender tropical surviving reliably only in zone 9 or warmer. (where it can be a pest in wildlife areas or a boon in sewage treatment)
This plant can be easily overwintered in the tropical aquarium with full grow lights and water kept around 72F.
It will likely elongate (the balls will turn into longer cylinders) but when split up in the spring, the babies will regrow new segments that are round.
You can find a ton of other articles about backyard ponds here.