In my zone 6ish area of MD, the duckweed eventually dies back in mid summer,
drops seed and disapears.

BV.

I always thought that duckweed wasn't hardy, but I added
no plants to the veggie filter this year and duckweed
appeared. I scoop it out regularly as a treat for the fish
- it doesn't last long with the koi.

--
Bonnie
NJ