I've got a pile of merino and I use the regular wash cycle with cold water and usual laundry soaps with no problems and some of it is 6-7 years old. Dry on medium heat.
One precaution:
After fishing a cold and wet day, I removed a new set of Smartwool and threw bot pieces in the tent vestibule before donning dry clothes.
Next morning, that set of underwear [$200] was full of large holes where mice/shrews chewed their way through. Hang em up!
