Walk the beach and collect semi dry seaweed that has washed ashore, putting it into a bag. Avoid harvesting seaweed directly from the ocean or from nearby reefs or rocks, which may be illegal in your area. Collect seaweed mid-beach. Collecting seaweed from the middle of the beach is your best bet. Seaweed that's mid-beach is far enough from the water to have had an opportunity to dry out somewhat.
Should you rinse the seaweed with fresh water before adding it to your soil?
Not necessarily. You can rinse the seaweed with fresh water but this is optional, according to many sources. Some advise not to rinse the seaweed, so that trace minerals from the ocean/sea can be added to the soil/potting mix.
Can you add seaweed directly to your soil/potting mix?
Yes, but it is better to dry the seaweed in the sun and shred in tiny pieces.
How to Compost Seaweed | Home Guides | SF Gate http://bit.ly/1t3lfwL
Seafood for the Garden: Make Your Own Organic Fertilizer: Gardenista http://bit.ly/1t3list
How to Use Seaweed to Mulch Your Garden | Eartheasy Blog http://bit.ly/1t3llEJ
Seaweed is the best garden amendment, hands down | Grist http://bit.ly/1vDEHGA
How to Harvest FREE Seaweed to Enrich your Garden with Trace Minerals - Growing Your Greens - YouTube http://bit.ly/1xQc1tj
Composting for Serious Gardeners http://buff.ly/1SMDCqI - 2016 guide