Not sure if you still need it, but here is a small hint. (Or something like that, I will try to put it into a spoiler, but it will probably not work on here.
Edit: Nope it does not. *Sigh* Guess I will just use line breaks. (Click on 'View Rest' for the Hint)
Hint: There is a mention of both type of flowers being set in a very particular shape. See if you can think about portraying that shape onto the grave stones (all of them combined).
Also: If there is more than one type of flower - and shape - this may also mean that there is more than one possible solution.
That with some trying around should hopefully do the trick.