I've made a farmer friend, who's accumulated a giant heap of seaweed. (There was a storm a few years ago and the beach needed to be cleared of seaweed.) He's encouraged me to borrow some to apply to my garden. This is all so much easier than going to the beach and hauling bags by hand and foot. Plus, it's already half-rotted, so it's much more garden-ready than what I get from the beach.
The benefits of seaweed in your garden according to a Guardian article: "As seaweed breaks down into the soil, it encourages microorganisms whose activities help convert unavailable nutrients into forms that plants can use. It increases chlorophyll production and contains many micronutrients important for soil and plant health, as well as acting as a growth stimulant: it is rich in cytokinins, plant growth hormones that work above and below ground, improving root growth." - "Want to boost your soil? Get some seaweed," The Guardian, Nov. 2016.