Staining a 4 year old greyish fence
 

I would like to stain the fence and would like to know how to clean it before staining. It's about 4 years old and turning grey. Is powerwashing an option or do I need to use some product?

There are cleaning products that can be sprayed on to the fence and after a short time rinsed away. They will change the color of the wood back to its original color at which time it can be sealed or stained and then sealed.:)