Cleaning exterior rough cedar walls

[Tom Keith]

hello All. I purchased home with a two stour addiction that has rough cedar exterior walls. The walls were left to the elements for some years and have turned almost black. I wondered if they can be cleaned with something like bleach/water and dried and re-sealed?  I hap planned for this when I purchased the home and now being told it won work.  I am attaching  photo for you to see. Thanks for all the hlelp.  Tom.