Seaweed is a great mulch or can be added to your compost bin BUT after you have gathered it from the shore you need to leave it to sit somewhere for at least two weeks to leach out the salt. If you don't do this the salt in the seaweed will end up in your soil - not a good idea. Probably the best way to use is as a mulch on your vegetable garden once it has lost the salt.

Hi Tengered
Nice little piece below about seaweed that I pulled out for you regarding seaweed and removing it from the beach.This was a botanist opinion when asked the same question

My first comment would be please rinse the seaweed off while you're at the beach! Otherwise you'll be bringing untold numbers of other plants & animals home with you and dooming them all to death by dehydration or starvation. Sure there's always lots of seaweed washed up on the shore, but it's usually still sitting within the 'intertidal zone' meaning that it'll wash back into the ocean at the next high tide and even if it doesn't, if it's old & dry, it still supports lots of organisms that live up on the beach. So, regardless where you've grabbed the seaweed from, please rinse it off to give those animals & plants a chance at survival.

Secondly, remember that (apart from its own self-advancement) each patch of seaweed is there to provide food & shelter for hundreds or even thousands of other species: baby clams shoals of fish, jelly fish, snails, crabs, and many more. And if you take ALL of the seaweed from a particular area, most of the animals that rely on it won't have any other sources of seaweed to rely on So, when you're out collecting seaweed to help your plants grow, please respect the natural balance & interdependence of the ocean community and try to limit how much seaweed you remove at any one time & from any one place.

Steve

Hi tengered,
I place a thick mulch on my asparagus bed in around sept and it's usually gone by may.
It mostly depends on what you wish to mulch. If it is on the veg plot there are instances where the salt would be relished. It can be placed around all members of the cabbage family and across the entire asparagus bed from autumn until spring, (once you have removed the ferns). I usually get a load and put round all my brassicas as soon as I've planted them. But anywhere else, rinse first. If you have an out of the way place, you could steep it in a bucket for a few months and then use as a liquid feed. throwing the final mush on the compost heap. But it's the worst stink possible so a lid would be a great asset.
If you have large areas of soil around plants in your borders, you could place rings of seaweed around them not only to mulch and eventually feed your plants but also to deter slugs and snails. But it does have a smell for a week or two.

It is also illegal to remove anything from a beach as almost every beach in Britain belongs to someone.
We used to collect the dried seaweed from above the normal highwater mark and there was no salt left in it and no marine creatures either.

Owdboggy you are right. You have to have a license to cut growing seaweed, but the stuff piles up above the water line is fine. I forgot to put that bit in.