Why Flowers?

I managed to take the daffodils to put on my Dad`s grave this afternoon, and it set me pondering – why do we put flowers on graves?

I know I do it, and it feels right to do it, but why? Why does it feel right?
I know that if I don`t do it, and especially on special days – birthdays; Christmas; Easter; anniversary of the date he died; before going away on holiday etc., I feel as if something`s missing, that I haven`t done something I should do.

I can always remember Dad saying once, about someone he knew who said “you can put a rice pudding on my grave after I`ve gone because I won`t know anything about it. It`s what you do for me now, while I`m here that matters”. And I guess that is very true.

Or is it?
How do we know whether or not they know what we do now somehow. Perhaps putting flowers on are the way of showing we still care, of trying to make up for things not said or done?