I use spent hops a lot, asI can get as many as I want from a local brewery. I find they make a great mulch and keep the weeds down well, although they do sometimes blow away when it's dry. I have used them round asparagus, but it is said that if they are fresh they should not be put near young shoots.
There are a few threads on here if you search. Dear ols Supersprout, a member who is sadly not with us any longer, loved using them.