I recently bought a lovely Ibanez fretless with an unlined rosewood board. It's been run with flats so the board is in nice shape. Although there is no real evidence of the rosewood 'drying out' I wonder if I should treat it with some light oil? Especially because it lives here in the Sonoran desert.
I give all my fingerboards a lemon oil treatment about once a year. All I've got is fretted ones though right now. Did the same to my fretless when I had it. Seems like a good idea being in Arizona
A decent rosewood board does not require oiling - it's a naturally oily wood. But after a while it can look dry and cruddy, so cleaning is a good idea. Assuming you use a gentle cleaner and not something that strips the natural oil out of the wood, nothing else is required. However, a drop or two of light oil will make it look better - purely a cosmetic treatment though. Fingerboards really don't get the chance to dry out. They are subjected to deposits of skin oil whenever they are handled. Unless, of course, you play with gloves on.