The problem with reeds is that they don't cover the ground much and I have to think about something that would do this. On examination of marshes pictures, ther is some growth, always the same kind which are water hyacinths according to my books, so let's see how we can do this.. First coat a bit of paper with some superglue, for strength
Just let dry overnight and detach the stuff from the glass with a blade and that's it! As the green stuff always stays kinda elastic, you won't break anything while cutting them out from the glass surface. The water lillies produced this way are very thin and certainly better than you could find anywhere else -even if using some laser cut paper, and I don't even mention photoetch.
Then use the bottom of your X Acto knife and press your ball flat on the greased glass surface (you can also use a tile for instance) using some bit of greased transparent plastic to avoid direct contact between the metal and the green stuff -otherwise the green stuff will glue to the metal of course!