Amazing how luck turns out sometimes! Glad I could, er.. help.
It says if you keep it fully immersed it should go beyond being seasonal. Also, there is no winter in your tank, and it's an outdoor N. American water plant, so I am sure the changing light and temp affects it's life. Those prolly aren't happening much in your tank
Let me know how it does, send us some pics, and hopefully I'll get to buy some from ya!
-MT