Seaweed contains plant nutrients, including potassium, (up to 12%) , but it is low in nitrogen and phosphate. It can contain in the region of 60 trace elements, growth hormones and other nutrients
particularly rich in iodine and calcium. Spraying seaweed tea is said to increase resistance to insect infestation. Seaweed has been used as a soil improver for centuries and is still used in the garden as a mulch, liquid feed and in making
compost. It is also available commercially both dried and as a liquid.
If considering collecting seaweed it must be noted that many countries have laws or regulations protecting the marine environment
and it is likely that these will cover the harvesting of seaweed.
In the UK the Crown Estate licenses sustainable, commercial harvesting of seaweed from areas of foreshore and seabed not privately owned. However, while commercial
harvesting of seaweed from areas of Crown Estate foreshore or seabed requires a licence, collection for personal use, in small qualities does not require a licence but the permission of the landowner will be required.
following guides are recommended for anyone thinking of collecting seaweed https://cdn.naturalresources.wales/media/686552/gn011-detailed-guidance-for-seaweed-harvesting-hand-gatheringenglish.pdf
Seaweed is a commonly used as a constituent in home composting in coastal areas. It acts as an activator speeding up the
compost process. If using a cold composting technique small quantities of seaweed can just be added to the bin in the same way as any other nitrogen rich “green”. There are mixed views as to whether the seaweed should be
washed to remove traces of saltwater or sand with the consensus being that it is not necessary. However, not all plants tolerate salt so if in doubt the seaweed should be rinsed in fresh water.
If using a New
Zealand or pallet bin, in which layers of greens and browns are alternated, the seaweed can be added as a separate green layer or mixed with other green material. Shredded or chopped seaweed cut in 1- or 2-inch will decompose in a few
weeks compared with six months or more for uncut fronds so, as with other materials, it is better to cut the seaweed into small pieces. If the contents of the bin are to be turned to aerate the organic material occasionally in cold composting or
regularly as in hot composting cutting the seaweed into short lengths will also make it easier to turn during aeration and speed up the composting process.