How long do you have filament sitting “in the open”? I mostly print with a single filament roll at a time, and just leave it on the printer. A 1kg roll lasts me several weeks. For long time storage I keep it in an air tight box with disiccant pouches.
But how long can I let it sit before I should start storing it with disiccant and/or drying the filament before use?
That’s a bit high. PLA still won’t care, but PETG will probably only print perfectly for a quite short time (maybe a day or two).
That said, depending on what exact blend it is, Silk PLA or other PLAs with additives might also have an issue with humidity.