Way Back Jack wrote:
I want the mulch that takes longest to break down. Available a
hardwood, shrubbery, pine, cypress, and cedar.

Which breaks down the slowest?

Cedar

Or is the shape more important: shredded vs. nuggets? Thanks

Shape doesn't matter as much as size.

I use cedar in most of my garden areas. After a few weeks the color
fades to an appealing natural brown wood tone. It's biggest benefit
though is how it keeps bugs away. It works great for that!

Patrick