In reply to Klemen:
Generally, granite cracks dry out very fast because, being impermeable, all the water is on the surface and evaporates off. Only if the crack is itself a drain, with a continual supply of water from above, will it remain wet. For that to happen the crack has to be very steep, with a source of water close to the top of the crack, or it has to be a corner with drainage off the walls into the crack. In an arid spot like Cadarese (of which I have no first hand experience) you should be fine.