In FarmVille Hanging Gardens (farm) your coins are no good. Of course, your cash is still usable. Not that it matters really, because everything costs trowels.
This particular currency is unique, in that you can craft it. It can also be found when harvesting various items around your farm. Orchards, groves and the various animal pens all give trowels. You can also find trowels when harvest your seeded land plots on your various farms.