Is it necessary to fill the cracks with sand or something else so grass doesn't grow between the stones? In Miami grass grows tall very quickly-Thanks

Filling the joints of the WalkMaker building forms is entirely a matter of preference. You can use QUIKRETE® All Purpose Sand, knowing it will need to be replaced frequently, QUIKRETE® PowerLoc Jointing Sand, with less frequent replacement, or a rigid material like QUIKRETE® Mortar Mix or QUIKRETE® Sand/Topping Mix for a permanent joint. The joints may also be left unfilled.