I am sorry that you are having a difficult time thinking about all of these questions. They would best be answered by the people who manage the particular garden that you are speaking about.
In my experience, when ashes are "scattered", it means they are sprinkled about, above the ground. Unless a tree or other plants were planted and they were scattered or tilled into the ground, in the place where the tree/plants will be placed.
Do you have a way to contact someone who was there? That is probably the best way to get answers to your questions.
Best to you,
Corinne