Friday, 6 December 2013

Fertilising a garden bed with seaweed

As mentioned in the first post we want to use seaweed collected from the beach to fertilise our garden bed.

The collected seaweed has been left out in the rain for one night just to wash some excess salt of it. Many people just throw the seaweed onto their garden and as far as I know it does not have a detrimental effect on the ground either. The seaweed should be still wet however, and the dried out stuff you can find at the top of the beach is not ideal for fertilising as the break down process is hindered due to the lack of moisture. Also the slimy alginate substance that leaches out from the seaweed helps the soil to stick together and retain more water without mudding up or becoming compacted and the dry stuff just doesn't have any of it anymore.

I also collected some blue mussels I found during an inspection of our boat mooring. They had grown to a phenomenal size on the rope under the buoy and were just enough for a little lunch before working out in the garden.

Pic 1: Delicious.....
The shells of these mussels were crushed between two stones and then spread over the freshly loosened garden bed.

We didn't pick out any of the weeds from the bed, unless they were the really tenacious ones like mint, brambles and some mombrecia. Weeds are nothing bad!! I always say this. They are only bad when you decide to make them your enemy. Every fibre of weed that grew in this garden bed took nutrients from the ground. I want those nutrients to go back into the soil and not take them out of the system.

So after the ground is loosened and the shells have been sprinkled on the soil for a long term calcium supply it is time to spread the seaweed. We covered the whole bed with approximately 3 inches of seaweed. If we would start a new bed we would probably go for 6 inches. This bed, however is already well established and the soil is quite rich.

It is important to leave the seaweed on top of the soil and not to till it under. If the seaweed is in the ground when it breaks down it can actually rob the ground of nitrogen to speed up the breakdown process, and that is what we are trying to avoid. So just leave it on top and let the worms do the job of tilling the nutrients into the ground. 
Pic 2: The finished bed
And we are done....yes, as simple as that. Over the winter months this seaweed will decompose and by spring time it will be time to cover the bed with cardboard and then more seaweed as a mulch. I guarantee you that there will be no weed poking through and your backs will be spared the tedious and frustrating part of weeding.

And here is the whole process in video form. 


  1. The seaweed looks great, I wish we had access to it for our garden, I plan to grow some sort of prolific water weed on the dam to provide mulch for the garden, but that is a plan for another year at the moment.

  2. This comment has been removed by the author.

  3. Thanks Jude,

    Yeah it is great to have seaweed. In our last place, we planted Elodea in our pond. I never planned on using it as a fertiliser/mulch, but it grew so fast that the whole pond floor was covered within the first year. We didn't have much Duckweed on the water, but some people use that too. It can grow so fast that you have a steady supply of mulch (if conditions are favourable).