Sent as a letter to the Editor.
I just thought it might be worth mentioning to your readers. I planted a variegated water reed grass (Variegated Phragmites) in my pond a few years ago (obtained from a pond supply place near us). I had it in a submerged pot. It seeded at the edge of my pond, and not knowing any better, thinking it looked great, I left it alone.
After about four years, I decided to clean out the pond and completely drained it. To my dismay I found several holes with sharp points protruding through the liner (30 mil EDPM).
After determining that it was some kind of plant, I pulled up the liner and discovered large (pencil diameter size) runners going completely from one side to the other side of the pond underneath the liner, with these needle sharp protrusions (much like a sharp pencil and just as hard) coming from the runners, pushing up against and through the underside of the liner. I’ve had to remove all these ‘roots’ (hope I’ve gotten them all) and replaced the liner.
Needless to say I won’t allow this in my pond anymore or anywhere around the edge of the pond. You might want to caution your readers about using this grass (or at least find some way of controlling it as I should have). The cost of liner replacement, as well as having to remove and replace the border rock, was high and shouldn’t have been needed.