Questions about dried seaweed

 

At the top of my garden I plan on planting some hollies (and a bare rooted dog rose) this autumn, the only concern I have to the growth of these plant in soil fertility, lots of things are growing up there and their very happy but I'm entirely confident they'll thrive. 

  Like I said in my previous post I was planning on using cocoa nibs as these have a good amount of nutrients, but I can't seem to find these anywhere, one thing I can find is dried seaweed (from a reputable seller), I just have a few questions about this as a mulch.   1) can I do a 50/50 mulch of seaweed and composted bark? (just to bulk it up and make it go further.)   2) will hollies and dog rose be happy with said mulch?    3) has anybody had success with dried seaweed?