Can’t recall why I started getting interested in seaweed as a green manure, although it came up in conversation on Monday night. One of my colleagues was talking about taking a cycle ride along the seafront from Edinburgh out to Seaton Sands, which opens up the possibility for doing a run out to collect a trailerful of the stuff.

Seaweeds and their uses, Chapman and Chapman. CEC Central Lending Library, shelfmark QK567. Technical book; reporting and links to research; graphs and tables; relatively old.

Mostly brown algae, wracks and oarweed has been used as manure. Driftweed or cut rockweed. It’s mainly used close to the coast as seaweed is approx. 90 percent water. High potash content (K) so good for plants that require high K: roots and fruit, esp. blackcurrants. Low in phosphate so must add it if seaweed used exclusively for long time.

N Phosphoric acid K Salt
wet weed 11 2 27 35
manure 11 6 15

Advantage of being free from weeds and fungi.

Seasonal variation: research shows higher content of minerals around March; lowest around October.

So … it’s actually seaweed as a brown manure. Quite different from getting well-rotted manure from Gorgie City Farm at £2 per bag. Telephone 0131 337 4202.

Organic Gardening; Plant life of Edinburgh and the Lothians; A Scot’s Herbal; Joy Larkom: all these references seem to indicate that seaweed is full of trace elements and so is useful for poor soil but doesn’t make much difference on good soil.


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