Grief affects us all in different ways, and we all handle it differently. I never had one specific outpouring of grief for my Dad; I'm just aware of it always there - not to say I can't get on with my life, I'm carrying on as normal but every now and then my memory of him surfaces - mostly it's fine, other times harder to cope with. I always thought there'd be a big load of grieving and then it's done - while I think some people have that, I've now accepted that for me, it's always going to be there in the background - but in some ways it can be comforting. The occasional dreams I have with him in can be a bit more difficult.
With all respect to the well-meaning kazza who kindly recommended that website, keep a note of it by all means but as long as you feel you can cope, just act as you feel is natural. If you wish to keep talking about your nan, do, but you may find it hard to do that right now, in which case, don't. As kazza also rightly said, there's no right or wrong - in fact it's one of the great levellers in life, we all experience bereavement and all have to deal with it in our own way.
By the way, don't do yourself down by saying you never grieved for your nan before. In your own way you probably were but, as you said, something like putting the flowers down triggers it in a different way.