Stable and indoor rugs every few weeks to a month. Like them clean, I change into stable rugs at night.
Turnouts are done daily when they come in, just straps and the edges get a dandy brush over which keeps them looking cleaner for longer, I do it when they are still on the horse. As for washing them hw's at the end of the season, lw's 3-4 a year, but they get replaced often.