Are you currently required to wear mask while outside in the gardens?

Not that I saw, only indoors

Just when you near to other people or other group, but if you alone or with family you can take it off

Only if you are not 6 feet apart Or not alone

Only when inside or near others.

The signs say "wear a mask when social distancing isn't possible"

Yes, inside you do. But outside you don't have to unless there slot of people passing you. Then they'll ask you.