Heath's Wikipedia entry has been changed again... last night it said he was buried next to his grandparents at Fremantle Cemetery. Now it says this:
Following the memorial, Ledger's body was cremated at Fremantle Cemetery; a funeral for ten members of his immediate family followed, and then his ashes were "scattered in a family plot at Karrakatta Cemetery, next to two of his grandparents
The entry for Fremantle still says this, however:
On February 9, 2008, the cremated remains of actor Heath Ledger were buried here.
An Australian news site reported this:
Following the service, 10 family members were given a police escort to Fremantle Cemetery for the cremation. Security was intense, with the windows of the small chapel blacked out... Ledger's ashes will be interred in a family plot at the cemetery, next to those of two of his grandparents.
In other words...

I saw a photo of the graves of Heath's grandparents at Karrakatta, somewhere on the internet, over the past fortnight and they weren't "graves," as such, at all. They were three small brass commemorative plaques, situated close to the ground, located in a rose garden. That's one of the options for disposal of ashes, offered by crematoria here in Australia. The ashes are scattered in a rose garden and a small plaque is erected at the site.
If this is what's happened with Heath's remains, it will be difficult to deliver a floral tribute on his birthday, because there's no real place to leave flowers. I like Peachy's idea to float a wreath at Cottesloe Beach on Heath's birthday. Apparently Cottesloe Beach was one of his favourite places.