Feeding Your Worms With Kelp

I am starting a project to use kelp in conjunction with my worm farming. Kelp is a giant sea weed, that is thrown up in great quantities along our coastline after every storm. I have already started feeding it to my working worms on a trial basis and intend expanding to a bigger operation soon.

There has been considerable scientific research into Kelp for a number of beneficial uses, in varied spheres of interest. Seaweed, such as kelp has long been the main source for agar-agar, a useful product that is essential for making Jello (Jelly in UK). Vegans also use it to provide missing elements in their diet. In the garden, Kelp is well known as a source of trace elements and kelp extract is sold for promoting healthy plant growth, particularly where soils are impoverished or lacking in certain minerals. It may be used direct to the roots or often sprayed on as a foliar feed – however the kelp extract is certainly not cheap.

My plan is to use vermicomposting to break down the kelp, so that I get a double wammy – the rich organic fertilizer from the normal worm composting operation and the extra bonus of adding all the trace minerals that kelp brings to the party.

I’ll keep you posted.


  1. steg

    Is this the normal big kelp, on atlantic coast? Isn,t it to salty?

  2. Steve

    Yes, the kelp that we are using, is the large variety that is used locally for processing agar-agar. It is thrown up onto the coast in considerable quantities, after a storm.

    The salt should not be a problem, we just give it a quick rinse to remove anything from the surface. I quote “capmatt 10+ on vermicasting forum: –

    “Plants in general don’t like salt, even plants that live in salt water. So most have mechanisms to get rid of excess salt.”

    Posted by captmatt 10+ (My Page) on Thu, Jan 29, 09 at 21:23 check out the URL



    • Add aloe vera too. I'm going to try.

      Add aloe vera too. I’m going to try.

  3. Steve

    Besides the beneficial supply of the trace elements and minerals, the kelp is rich in the basic fertilizer requirements of nitrogen and potash. However, from all accounts it seems to be short on phosphate.

    I am not sure if there would be any merit in feeding some bonemeal to the worms, as it is a straight organic supply of phosphate – or should I just add it to the soil together with the worm castings, when I prepare my planting bed.

    Any suggestions?

  4. African

    Kelp powder is sold as a garden enricher in the US, for digging directly into the soil. In South Africa there is a commercial product, called Kelpac, sold in liquid form that is used diluted as a foliar spray or can be added to the soil via the watering can. These products are used to supply trace elements and plant growth hormones that promote root growth.

    Useful links are http://www.taurus-products.co.za/


  5. forsyth

    Can’t you just compost the kelp in an ordinary compost bin? Does it stink?

  6. African

    Feeling a bit depressed, the worms in the kelp experiment have been taking a bit of a set back. Numbers have reduced and worms seem lethargic and not happy.

  7. African

    Checked worms again today – I see some tiny worms, if they’re breeding they must be ok. Will continue experiment, but take more care to wash kelp. Will also prepare some pre-composted kelp, by conventional methods for later feeding.

  8. African

    Worms still seem ok – seem to be getting used to kelp

  9. Steve

    No change – worms not really prospering. Numbers not increasing.

  10. forsyth

    I think you need to just compost the kelp in timber bins and use some of the product to feed your worms – in meantime put them on another diet

  11. Steve

    Yes – I’m going to do that. Might as well cut my losses

  12. Steve

    Still no meaningful progress – feeding worms on kitchen scraps, while waiting for kelp to compost.

  13. African

    It would appear that although kelp is a valuable source of nutiments, trace elements and minerals, the use of it requires some pre-processing to make it practical. Kelp is quite tough and leathery and becomes as hard as wood when it dries out.I simply chopped up the kelp and bashed it a bit with a mallet, but the worms did not prosper. Precomposting seems the most practical, but some kind of mechanical mastication using a garden shreader or similar seems indicated to speed up the process.

  14. Steve

    Weather is cold and kelp heap not composting yet

  15. Steve

    Still hoping that I will get useful kelp compost – but rain keeps compost heap too wet and it is still too cold

  16. Derek

    Hi steve.
    Put a cover over the kelp. I do with mine and it works much quicker in cold conditions.

  17. Stephan

    Hello Steve,

    I am all for composting but as is has been mentioned before salt is harmful to worms and you should first compost the kelp. This works best as Derek mentioned if you cover your compost pile. Then you have to turn it every 4 to 5 days and if everything goes well you should have finished compost after about 15 to 20 days.
    The kelp compost should then still be washed with water a lot to remove as much salt as possible.

    You can add other organic waste products to the compost. The more variety you add the better your final compost and worm castings will be.

    Good luck and happy worming

  18. Cornel

    Hey Steve & African,

    Pre-composting organic matter is essential to any mid-scale worm farm.
    Eisenia Fetida hate fresh inputs, like fresh leaves or manure.
    I recommend you hot-compost the inputs before-hand.

    I know of an operation that purchases fine kelp (6mm/ 3mm), and uses it as an amendment of only 2-5% of the inputs where 90% is composted material.
    You want to diversify inputs.

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