Seaweed as a fertilizer?

We don't live near the sea, otherwise I would be down on the beach like a shot collecting this wonderful stuff. Material collected from above the highwater mark may be dug in straight as it is, any salt has been washed out of it. Fresh green stuff can be composted or left for the rain to remove the salt before using. You can make fantastic liquid fertiliser from it too, just stuff as much as you can fit into a barrel and fill it with rainwater, Cover and wait until it rots down. Dilute the lquid and away you go.
It has been used for aeons by farmers from the Shetland Isles to the Channel Islands

Now you are making me feel guilty - I shall have to trek down the track to the 'beach' with a black sack and collect some! It is about a mile, and of course Henry has to come too, that's why I haven't collected any. Our seaweed isn't green, it's the brown stuff - bladderwrack? Does that make any difference?

No difference at all. When we lived n Somerset, it was a car drive down to Blue Anchor Beach where we collected tons of it!

Well, Owdboggy, you know what our part of the world is like then, if you lived near 'our' coast - beautiful, isn't it. I shall certainly try to collect some seaweed now I know that it's useful stuff. Free, too!