I don't know how much salt the seaweed will bring in, but if you believe it does have significant salt...I have composted beef feedlot manure in semi-arid locations where we saw significant salt accumulation in manure, and it was further concentrated as a result of the composting process. It didn't hurt the composting processes, but you have to be careful how much you use on your soil, so you don't wind up with excess salt accumulation in the root zone.

I did a little research on this myself as I live near the gulf and have been meaning to gather some seaweed. I would definitely rinse it to get the critters off such as snails, barnacles etc and saltwater. The water inside the seaweed is fresh water. I have read many people just mulch with seaweed then topdress with soil.

I am hopeful that the sea weed will be a good source of trace elemets. I have read that it is a good practice to incorporate a diverse mixture of organic materials when making compost to insure a good mix of trace elements and minerals.

There is no answer. I searched "what is the sodium content of seaweed", but it depends on the type of seaweed and even then there are no answers, so I would not use it. While it may have some trace elements there are other sources of trace elements. It is too risky. I would not do it if were you. I think the bad potential for over salting your soil outweighs the benefits of seaweed.

I've been using it for years. It holds a lot of water, and makes a slimy mess if you just layer it in. I let it sit outside to dry, then run it through a chipper/shredder - it turns into a fine powder. I also use it as a mulch on asparagus. It is common practice in Ireland to spread it on gardens and fields. There are regulations in many states regarding the collection of seaweed, so double check.

Sounds like others have had no problems with it, but if you are worried about it, you could have your first batch of finished compost tested to determine the soluble salts level. Its usually a pretty cheap test.

For eons people in Ireland, Scotland, and probably other coastal areas have hauled seaweed in to make soil. It can be very good. The seaweed probably should be rinsed off before composting, just to be sure the amount of salt is kept to a minimum.
I suspect that the ratio of organic matter to manure in your mix may be kind of light, so I would add more seaweed if it was available to me just to get to that 3 to 1 ratio of vegetative waste to manure.

I have not been able to find anyone who has actually used sea weed and had a salt problem because of it.
Anyone familiar with the work of Doctor Maynard Murray?
He pioneered the use of mineral salts from dehydrated sea water as a fertilizer over 30 years ago. I understand that the salt is not a problem because it is buffered by all of the trace elements and minerals.
I have to say that I am quite pleased with the way that the compost is heating up.
I checked the pile today and it was 152 degrees.

I don't wash seaweed. A caveat: I garden on sand. Heavy clay might require different methods.
From what I've read, seawater is actually quite low in sodium chloride (the bad salt). The rest of the salts are generally very valuable in the garden.
Seaweed is great stuff, it contains most of the micronutrients that have washed off the land.

If someone has ever ended up over salted from sea weed, I would like to know about that. How do you test for sodium? I could get free sea weed since I live near the beach by a few miles, but it would be this big kelp stuff that would not breakdown quickly. The huge kelp would be more work for me then other cool things free things I can add like fallen fruits. When you see this stuff it is huge hard slimy and often has a lot of flies on it. If it had fly eggs that would be even worse. I don't want flies hatching in my compost. It would mean maggots eating my compost and maggots eat a lot more then worms. It would not only be gross but less compost for me. If I could get the kind of seaweed they make use to roll sushi that might be acceptable if it had no fly eggs. But, I don't think it grows much around here. I don't know, I never thought to look for it.

The original question was whether the percentage could be increased and still allow the pile to heat. It's a high nitrogen green, so if you add more the pile will get hotter. Don't overdo or it may get too hot, which can affect the microbial population and lower the quality of your product. Or it can go anaerobic like a pile of grass clippings and start to lose N as ammonia. You'll know if you've crossed that line.

Seawater is about 3.5% by weight dissolved salts. 80% of that sea salt is sodium chloride.

Nice graphic illustration:
http://en.wikipedia.org/wiki/File:Sea_salt-e-dp_hg.svg

I have not composted seaweed nor have I heard anything for or against it beyond what is in this thread, so I'm just reporting. I would not put a lot of sea salt on my garden as a fertilizer, since I have clay. But a little that comes along with wet seaweed, no big deal. Certainly not worse than salty cow manure compost.

Thanks everyone for all the info.
What temp. would be considered too hot?
I have been monitoring the temp. daily and it has been pretty steady around 152 degrees for the last few days.
This is a few degree's above the temperature's of my last two composts. They peaked at around 146. It must be the sea weed that is causing the higher temp.
I did add quite a bit more fresh from the ocean sea weed in this last batch. The other compost's had a fair amount of eel grass that had been washed up for quite some time before I harvested it. I am hopeful that I can have finished compost in time to use early this spring.

Yes with 90+ minerals sea salts are very good for your plants!!!!

You could even do a separate batch of just composted sea weed ensuring to include it in your plants nutritional program.

If you have the space, making separate composts with differnt NPK ratios can Allow you to produce higher results. For example, if you composted only Banana you would know that compost is high in P and K and Ca/Mg which is good for the flowering of plants. Stopping the use of your high nitrogen compost and increasing your high K compost for fruiting/flowering plants will allow for larger harvests.

I had thought about making a sea weed concentrate compost made with a much larger % of sea weed.
What would a good carbon material to use? And what ratio of sea weed to that carbon material would be optimum?
I have collected some eel grass that had been washed up for quite some time and appeared to be partially composting on its own. Some of the fresh sea weed that is dark red / brown is really dense and compacted.
I think it would need to be mixed with somthing to get it to compost well.

How did the seaweed compost turn out? I'd love a follow up please.

M

I used lake weeds in country compost piles for a couple of years. Quite a large percentage, with shredded leaves and cow manure.

Those years the country tomatoes did well. Maybe not as well as my city tomatoes without lakeweed in the compost piles, but the city tomatoes got more TLC.

No concerns about the salt of course. If I had access to sea weed, expect I'd use it after rinsing.

While some people recommend rinsing seaweed before using in the garden, they seem to do so on general principle rather than from any evidence. I'd use all I could get my hands on, and not worry about salt. You'd have to use massive amounts before it would cause a problem in most soils.

I second using all I could get my hands on. It's gorgeous stuff, makes a nice hot pile, and no problems I've found. I love in coastal city, but there is rarely enough to collect, and there's no law against it as far as I know here. Every few years or so we get a massive amount on shore and I was in seventh heaven. My marine biologist friend tells me it happens every 5-7 years. I'm waiting for the next time, ready with shovels and bags and all. The municipality just brought bulldozers to get it off the beaches away from the people as they thought it an eyesore and icky. I got some funny looks from the bulldozer guys, but I'm used to that.

jonfrum: I totally agree on the need to 'rinse', it does not seem essential to me. As the Greek scientist Paracelsus said, 'The dose makes the poison!'