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How to Use Seaweed to Mulch Your Garden

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Seaweed is among the best gifts nature makes available for the gardener.

By Greg Seaman, Posted Sep 18, 2010

Seaweed is among the best gifts nature makes available for the gardener. Seaweed will benefit your garden any time of year, but it is especially useful as a mulch to protect plants during hot, dry weather. In our garden, we’ve come to rely on seaweed as a valuable, yet free, source of fertilizer, mulch and organic pest control all in one natural material.

Benefits of seaweed for gardening

Gathering seaweed for the garden has always been a favorite outing for our family. We usually take a small skiff to a nearby beach and load up with as many sacks as we can safely transport home. It’s fun for children, as they can participate as well as an adult, or they can simply enjoy the beach while we gather the seaweed. As we fill up our sacks, our thoughts drift to the many benefits this will bring our garden.

  • Saves water, keeps soil moist at ground level

    The purpose of any mulch is to keep garden soil from drying out at the surface. And by preventing moisture from evaporating, mulch reduces the need for watering. The practice of mulching is essential in areas where conditions are hot and dry.

  • Eliminates the need to weed
    Mulch covers the soil and blocks new weeds from sprouting. Because the soil beneath the mulch remains moist, any weeds which do manage to sprout through the mulch are easy to pick.
  • Repels slugs and other pests

    Slugs are immediately repelled by two things – salt and sharp-edged materials. Seaweed has a natural salt content which repels slugs, and within a few days of application it dries and becomes quite crispy. Slugs do not like “crispy” surfaces, as the sharp salty edges cut into the soft body tissue. While some mulches may provide hiding spots for slugs, earwigs and other pests, seaweed mulch does not have this disadvantage.

  • Enriches the soil
    Seaweed is a broad spectrum fertilizer that is rich in beneficial trace minerals and hormones that stimulate plant growth. Seaweed is high in carbohydrates which are essential building blocks in growing plants, and low in cellulose so it breaks down readily. Seaweed shares no diseases with land plants.
  • Boosts lethargic plants
    Seaweed fertilizer contains an abundance of fully chelated (ready to use) micro-nutrients which can be readily absorbed by plants without any further chemical decomposition needed.
  • Helps lighten the soil
    Compacted soil can benefit as seaweed mulch breaks down. As the material becomes incorporated into the soil, aeration is improved and the soil becomes more crumbly and moist.
  • Does not contain weed seeds, unlike bark mulch
    Two years ago we used commercial bark mulch to cover our garden pathways for the purpose of blocking weeds. Today, these pathways are sprouting horsetail, an invasive weed which can be difficult to eradicate. Seaweed does not bring any foreign weed seeds into your garden.
  • It’s free!

But what about salt? Is this a problem?
We have been using seaweed as mulch for many years and have not seen any adverse effect, such as a salt overload in the soil. In our region we have plentiful rain. If you are concerned about salt, seaweed can be spread out over the driveway and rinsed with a hose. Of course this is not an issue if you are using freshwater lake weed.

Gathering seaweed for use in the garden

  • Gather ‘mid-beach’
    Seaweed is often found scattered on the beach from the water’s edge to the highest point of recent high tides. The seaweed ‘mid-beach’ is drier than seaweed at the tide line and therefore lighter to carry. It also has fewer bugs than the seaweed high up on the beach, and is a little more pleasant to gather.
  • Use fine, broken up seaweed
    Look for patches of seaweed that are smaller in leaf size as this will be easier to apply as mulch. Set large kelp fronds aside – the wide pieces are difficult to form around plants in the garden beds. The kelp can be used to make ‘kelp tea’ and used as a foliar spray to deter insect pests.
  • Use onion sacks or woven poly bags or buckets
    We like onion sacks for gathering seaweed because they are lightweight, the water drains out easily, and they are easy to grip. They are also small enough that we don’t overload ourselves with heavy sacks. Woven poly bags are great if you can find them – ask at your whole foods store because these bags are used to ship whole grains. Don’t use plastic garbage bags as they are too difficult to handle. Your hands get slimy when picking seaweed and this transfers to the bag making it slippery.
  • Limit your impact by picking lightly from several areas
    Each patch of seaweed provides food and shelter for many small marine species. Pick no more than a third of the seaweed from any patch, and move on to another spot.

Applying seaweed to your garden beds

  • Apply seaweed within 36 hours of gathering
    Seaweed breaks down quickly, especially when in an enclosed sack. If you leave the seaweed in the sacks too long, it gets sludgy and slimy, and is more difficult to spread evenly over the soil.
  • Apply thickly, at least 4 – 6” deep
    Spread the seaweed thickly and evenly around the garden beds to cover any exposed soil. You may think you’re adding too much, but in a few days you will think otherwise.
    In this picture you can see the bare spots showing how much the seaweed has shrunk after the first application. Only a few days earlier, the seaweed was 4 – 6” deep with no soil showing through.
  • Reapply in one week, another 4 – 6” deep
    Seaweed shrinks when it dries. Even a generous layer of seaweed will dry in a few hot days to expose much of the soil. The seaweed will become very stiff and crispy. Ideally, you should reapply in a week or so, and this second application will dry out but still provide good coverage for your soil. Once we make the second application, our beds are usually well-mulched for at least 4 – 6 weeks even in hot, dry weather.
  • Leave a clear space around plant stems
    Once you have spread the seaweed around the plants, push it back just a little from the plant stems so they are not in direct contact with the wet seaweed. Once it dries, the seaweed will naturally ‘shrink’ away from the stems, but it’s a good habit with any mulch to keep plant stems clear.
  • It’s OK to mix seaweed with other mulch
    We use whatever mulch we can get, and it doesn’t matter if you mix several varieties of mulch on a garden bed. For example, our tomatoes are mulched with dried grass clippings (straw) and topped with seaweed. In the fall we’ll add maple leaves. Mix and match, it matters not.
  • Don’t use seaweed to cover garden pathways
    Some people use seaweed as a pathway mulch but this is a waste of good seaweed, which is better used on the garden soil for the reasons listed above. If seaweed is used on pathways, it quickly thins out to allow weeds to get through. And the seaweed will become very slippery underfoot after a rain.

Other uses for seaweed in your garden

  • Save kelp for making kelp tea
    You can put kelp, or any seaweed, into a bucket or large glass jar and fill with water. Leave this in the sun, covered, for a few days and your ‘tea’ will be brewed. Use this as a foliar spray to deter insect pests, or apply directly to the soil around seedlings. Bear in mind that this concoction will smell bad, so be sure to store it downwind!
  • Use seaweed for sheet composting
    If you have a good supply of seaweed, it is ideal for composting directly on a garden bed which is being prepared for planting. In our garden, we use seaweed to suppress green manure which is grown in the bed as a fertilizer and soil conditioner. The problem with growing green manure directly in a raised garden bed is digging in the finished green manure prior to planting without putting stress on the sides of the bed. Our solution is to ‘smother’ the green manure with seaweed for several weeks. This breaks down the green manure, with minimal disturbance to the raised beds or the soil organisms.
    In this picture, the bed on the right has ‘green manure’ fully grown and ready to dig into the soil. The bed on the left was identical before we added seaweed to smother the green manure, speeding its breakdown and making it easier to incorporate into the soil.
  • Use seaweed as a supplement for chicken feed
    If you have chickens, seaweed has a hidden benefit. Simply drop the sack (it must be porous, like an onion sack or woven poly bag) on the ground in the chicken yard. The next day, roll the sack over with your foot. You will likely see a cloud of insects emerge, freshly hatched sand fleas and other little bugs. The chickens will feast on these bugs! You can repeat this for a few days, then put the seaweed, which will now be sludgy, into the compost.
  • Put seaweed in the compost as well as in the garden beds
    When gathering seaweed for the garden, save a couple bags for the compost. This will help build and condition your compost with trace nutrients. While the instinct is to use your precious seaweed directly on the garden beds, you will get equal value from the enriched compost in a few months. This picture shows seaweed being mixed into compost.
  • I realize that seaweed is not available to gardeners living away from the coasts, and I was a little reluctant to even write this article. But each region of the country has different advantages and disadvantages for the gardener, and making the most of what is locally available is essential for those looking for sustainable solutions for gardening.


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  • Rula

    lovely article, thank you.

  • Cary Bradley

    Thanks so much for writing this article. I do live near the coast and very much appreciate you answering my many questions regarding how to incorporate this nutrient dense fertilizer to my organic vegetable garden!

    • Greg Seaman

      Thanks Cary. If you are some distance from the shore, you can ensure there will be seaweed to collect by checking the local wind report. Onshore winds will deliver seaweed to the beach. Offshore winds will often leave the beach empty of seaweed.

  • natalie l

    Has anybody been using seaweeds to much on tomatoes and peppers and others vegetables? Can i much my bananas trees that way?
    I have been told that the salt will kill them. I live in Florida and we do have have much rain at this time of the year ( but a lot of seaweeds!), should i rinse the seaweeds before using them?

    • Greg Seaman

      Yes, we use seaweed as mulch for tomatoes and peppers (see picture at top of this article) and most of our other garden crops. We have been using for 30 years and consider it the best mulch available to us.
      I have heard people's reservations about the salt. However, this has never been a problem for us. Some people rinse their seaweed before applying to their garden beds, but we have never bothered.
      I have never grown bananas so I cannot give a conclusive recommendation, but I would expect that seaweed would be a good mulch for them.

    • Arnis Krums

      I tried seaweed on Ensete Murelli this year. Results are amaizing, Ensete is growing like mad. I live in Ireland.

  • Sitka_Rose

    Alaskan gardeners have used seaweed for ever, but I never knew why they used it. Thanks for filling in that part of my education. And by the way, I love your site! :o)

    • Greg Seaman

      Thank you!

  • Alice

    I’ve been using seaweed for my garden for years but not like this! Love it.

  • Seaweed

    The substances secreted by soil bacteria in the presence of seaweed include organic chemicals known as polyuronides. Polyuronides are chemically similar to the soil conditioner alginic acid, whose direct effect on the soil we have already noticed, and themselves have soil-stabilizing properties. This means that to the soil-conditioning agent which the soil derives from undecomposed seaweed — alginic acid — other conditioning agents are later added: the polyuronides, which result from the decomposition of seaweed.

    Auxins in seaweed include indolyl-acetic acid, discovered in seaweed in 1933 for the first time. Two new auxins, as yet unidentified, but unlike any of the known indolyl-acetic acid types, were also discovered in 1958 in the Laminaria and Ascophyllum seaweeds used for processing into dried seaweed meal and liquid extract. These auxins have been found to encourage the growth of more cells — in which they differ from more familiar types of auxin which simply enlarge the cells without increasing their number. One of the auxins also stimulates growth in both stems and roots of plants, and in this differs from indolyl-acetic acid and its derivatives, which cause cells to elongate but not to divide. The balanced action of this seaweed auxin has not been found in any other auxin.

  • kathryn karmen

    As I do not live near the coast, I only gather seaweed when I have the occasional opportunity. I have only used seaweed in the spring and summer as you have described, but I was recently on the coast during the Christmas holiday, and never one to miss an opportunity, I now have a nice big bag of it in the back of my car. I was planning to just toss it on my raised vegetable beds for the winter and let it leach into the soil. I am wondering, however, if you have other ideas/suggestions for winter application. Would it be more fruitful to add it to the compost pile or save it under cover to apply as mulch in the spring, or….?

    • kathryn karmen

      okay. Thank you

    • Greg Seaman

      I think any of the three options you mention will be of benefit to your garden.
      In winter, during the rainy season, we put new amendments such as seaweed into the compost. This is to ensure the rain doesn't wash away the valuable nutrients we've worked into the soil.

  • Barbara

    Very helpful, especially to learn that you dont have problems with salt. I live on the south east coast of Australia and have ample supplies of sea weed but have shied away from seaweed collection and soaking because of the smell and my uncertainty of its effectiveness. But as mulch: Perfect
    Thank you, I’m glad you decided to go ahead and write the article.
    It’s well written, simple to follow and full of good advice.

  • Alice Sievers Rodriguez

    I have read on several other organic gardening sites that you DO NOT have to wash the seaweed. Now, there will people you will not be able to convince but hey, it’s YOUR garden. Do a small plot and see what you think. 

  • Thank you for the information.  I have always wondered if I could use seaweed but worried about the salt.  it will now be my new mulch!

  • Daisy

    Please dont pick ANY growing seaweed from the rocks !  Only the washed up stuff  !

  • Bev

    This is an awesome topic, and you answered many questions that I may have had.  I live only about an hour from the coast, and this really has me wanting to rev up my truck, and take a trip!  Thank!

  • Shoalcove22

    I live on the east coast of Canada where fall and winter storms deposit piles of seaweed at the foot of my lawns.  Every time I have added it to my gardens as top dressing, the plants have stunted or yellowed and died off.  I have tried fresh seaweed, seaweed that has been washed all winter by rain & snow and seaweed tea.   Sometimes I can get away with putting a layer in the bottom of new raised beds.  I tried it on several tomatoes in my greenhouse and they just died!   What am I doing wrong?

    • I just came in from mulching my tomatoes with seaweed to read your comment. Seaweed is usually a trouble-free amendment. At first I thought maybe you were getting a nitrogen overload from too much shallow-water fresh seaweed. I suggest that you try setting some seaweed spread out under the sun and let it dry for a few days, then try it on a small spot in your garden.
      But if the seaweed tea and seaweed that has been left out all winter still prohibits growth, then it sounds as if the seaweed has some toxic property. (Assuming you are using mixed seaweed, not a single species. If the seaweed you are using is all from the same species of plant, then there may an inhibiting property in that species. But seaweed usually occurs as mixed.)You may consider taking it to your nearest agricultural extension for testing.
      Here we use seaweed that is fresh and some that has been dried on the beach for a few days. We prefer the dried seaweed because it is easier to carry up the hill to our place, but both fresh and dry seem to perform the same. It has been quite reliable for us.

    • Two Green Thumbs

      collect large amounts of dried seaweed burn it it all in a large 44
      gallon bucket ‘n mix the ash with water and apply to your garden for
      extra nutrients people have been doing it for hundreds of years. if
      you’ve ever seen seaweed fertilizers in the shops that’s all it is…
      hope i was some help 😉

      • Interesting! Now here’s an idea about seaweed I had not heard of. Thanks for your comment.

      • bob cusa

        can you tell me where you live I live in florida and I don’t disagree with you but zones play a part thank you

  • Seaweed is excellent, even the powdered kelp, broadcast into the soil throughout the season!

  • Lisa D

    Thanks for the article. I have seaweed that washes up in my yard after high tide and storms…trying to find a use for it. We have a lot of seaweed and it is nice to have some way of using it.

  • Steve

    Great to read Greg Seaman’s article. It answers my questions about using seaweed in the garden. I work in the only Traditional Seaweed Baths in the United Kingdom (Soak Seaweed Baths, Newcastle, County Down, Northern Ireland) and grow my own vegetables. So I will be hitching up the trailer and taking a load of used seaweed home regularly from now on.

  • Sue

    Thank you for this article. I found it extremely helpful! I often take my dog to the beach and met someone, recently, who told me seaweed was the best thing for gardens. I collected 2 bags today, then realised I didn’t have a clue what to do with it! This has really helped and I’m hoping this year is drier than last and I’ll have a decent crop of veg and fruit. Will be going back tomorrow, with the rest of my bags, to stock up and then get the soil prepared.

    • Glad you can use the information. Thanks for your comment.

  • I live near the coast of Maine and just hauled 4 trailer loads today. There is a lot on the shore from the wind storms this past winter.

  • Thanks Vicky. You’ll find seaweed to be a real asset in gardening.

  • elaine Ritasdaughter

    thank you so much for this fantastic information. I live on the Costa Blanca in south Spain and the city council clears the seaweed off the beaches so the tourists have nice clean sand to sunbathe on. If I get up early I can get to the beach before both the tourists and the beach ‘cleaners’ to collect seaweed to help my veggies along.

    • Nice! Seawed is such a gift to the gardener.

    • william mosler


  • Margie

    i live on the East Cost of Australia and have access to a much sea weed as I can gather. Is it OK to use on succulents and cacti?

    • We have no experience using succulents and cacti but it would seem problematic compared to seaweed, which is plentiful, easy to handle and breaks down readily into the garden soil.

  • Wow, sounds like you’ve got quite a production. We were just gathering seaweed yesterday too. We don’t bother to rinse the salt, it sems fine the way it is. Amazing how it shrinks so much when dry – we add about 6″ at least and in a week it’s thin and the beds need more!

  • The seaweed will be a great mulch for your garden. Lay it on directly about 4″ deep or more. A few days in the sun will reduce it by half. You may want to then add more to cover any thin spots.
    If you have more mulch left over, add it to the compost. Seaweed mulch can also be applied around the base of fruit trees and small plantings.

  • Trish Bell

    I am going to prepare my lawn in Sept. for putting up a polytunnel in the Spring. I live in the Highlands of Scotland not far from the beach. I was planning to cover this area of lawn with thick black plastic to kill the grass, and then dig it and cover it with cows dun and sea weed, and replace the black thick plastic covering until the Spring time. Will this work? Do you have any thoughts on how I could improve this idea. Thanks so much.

    • Sounds like you have it figured out pretty well. The plastic will solarize the lawn and yes you will have to then dig it to break up the clods and see what lies beneath (rocks, debris). The seaweed and manure will be excellent additions and covering them till Spring will keep the rains from flushing the nutrients from the new ground while helping keep some heat to aid in breakdown. You might want to add some rock phosphate at this point, and in spring a soil test might reveal the need for lime. Your soil is probably acidic.

      • Trish Bell

        Thank you Greg for replying so quickly, and for helpful advice. Trish.
        Subject: Re: New comment posted on How to Use Seaweed to Mulch Your Garden

  • No idea. We just use what floats in. The smaller shredded bits are easiest to work with.

  • Peter

    Hi Greg, Thank you for such a detailed and simple to understand article. I have only started to use seaweed in the garden last year. By the way I live in Ireland and there is no shortage of sea weed. My question is can I just collect it off the beach, rinse it off and then lay it on the soil now that I have just taken out the last of the crops. Do I just leave it on the top of the soil or do i dig it in immediately or does it matter. I was thinking of making a big bin of “tea” as well. Can I then use it as a liquid fertilizer during the growing season or is it too strong and need to be diluted. Any help would be great.

    • Hi Peter,
      Top ‘o the morning to you over there in Ireland!
      Yes, you can collect the seaweed and just set it down on top of the soil in a layer 6″ thick if you have enough. A few sunny days will shrink this quickly. There is no need to till in the seaweed, it will break down gradually and any bits left over can be tilled in when you are ready to plant a new crop.
      While you are at it, add some seaweed to the compost.
      Seaweed tea is a good amendment. We put some in a bucket about 1/3 full and top up with water.
      If you are gathering a large amount from a beach, it can be helpful to throw it on the shore above the tide so it can drain and dry somewhat, then come back in a few days to collect. It will be drier and much lighter to bag and carry.

  • Marian Roth

    Thanks for all your suggestions. I live on cape cod–lots of seawee. My question is about garlic. I am about to plant my crop before the winter and am wondering if I should line the bed with seaweed before I plant the cloves. Thanks for any feedback h u can gie me. Marian

    • You could put down a 6″ layer of seaweed and mix it well with soil. By the time the garlic puts roots down the seaweed should be incorporated into the soil. Be conservative with how much seaweed you add.

  • meinmaine

    Great and helpful article. I happen to live within a couple minutes drive of the ocean so this was perfect!!!!

    • You going to find that seaweed is a great asset to your garden!

  • Tony Clark

    Great article Greg I have been thinking about using seaweed for a couple of years as I live just down the road from a beach in West Wales. We have just had some big storms beaches covered in seaweed at the moment picked four big bags this morning decided to give it a go. I know they use it in Jersey for their early potatoes. Do you think it an advantage to use a couple of mulches a year?

    • Yes, Tony. If you have enough seaweed, two mulches per year will be of great benefit to your garden.

  • Thanks for such a great informative article. I live on the North coast of Tasmania where there is abundant access to seaweed. I’ve used it successfully on my flower beds and want to use it in my composst too as ‘brown’ which i always seem to be low on, but I am worried the salt might affect/deter the worms?

    • We add seaweed to the compost regularly and have not noticed any decrease in worm activity. Seaweed is a great amendment for compost. If you are still concerned about salt, then you can always dump the seaweed on the ground and rinse it with the hose.

  • JWelton

    As a youngster, I knew an old hermit on Ocracoke Island in North Carolina who drug up seaweed and put it on his garden that was just about pure sand. I can’t remember exactly what he planted, but it was green and flourished.

  • Oscar Meyer

    Check your fishing synopsis in Oregon and possibly Washington (I’m not certain there) to avoid a potentially costly ticket. A shellfish harvest permit is required to collect seaweed.

  • I live on the West Coast of Canada in Victoria Bc. We just collected Kelp from the beach after spending a beautiful May day on the beach with the kids. I heard kelp was good for compost and we just built a compost bin with our kids out of free pallets! So we gathered as much up and wrapped it in my old tank top. It was 22 degrees celcius so i wasnt wearing it anyway. We brought it home and my 7 year old tossed it in. Thanks for confirming for me about the benefit of kelp in compost and now we will try it as a mulch. I had to write as people are writing and using kelp from all over the world….Cool!

  • I’m not sure how much is in a ‘cube’, but it sounds like you’re off to the right start. The soil test was a good idea.
    Pretty much any new garden will need some NPK adjustments, and nitrogen is key to get started. So working in the manure is the thing to do. Work in the kelp when preparing the soil, and save some for mulching once the plants are up. You probably need some rock phosphate as well. Sprinkle this on when preparing the soil, you can’t overdo it.
    My suggestion is to start with a smaller bed and keep notes of the improvements you have made, then plant this bed and see how it does. Then apply your learning to the rest of the plot.
    Make sure the chicken manure is well-rotted and fully composted before planting, since chicken manure is hot and can burn seedlings if applied before it’s ready.

    • David

      Hi Greg, a metric cube is about 3 feet, by 3 feet, by 3 feet (or what would fit on the back of my Toyota truck. Went to collect some kelp on the beach today, so we have it dried as well as very wet kelp, what I just now realized is sea bamboo, which is native to the southern Atlantic coast line. Would that be fine?
      Next step I gather would be to hose it down to get most of the salt off, and then chop it up and leave to dry. What do you think?

      • Hi David,
        I have no experience with sea bamboo, so cannot offer advice on this. But we use whatever seaweed that washes in, and have no problems with any of it.
        It makes sense to give it a spray to wash off the salt, but we use seaweed straight off the beach without rinsing, and apply it wet the same day. And we don’t bother to chop it up. This has worked for years, and the garden seems to benefit with no ill effects.

  • Thanks for the article. There are miles of seed-weed(not sure which variety) on the coastline in St.Vincent. I came across your article searching for the best way to utilize them in gardening.

  • bermudapilot

    I have been looking into identifying the main types of seaweed and eel grass in my particular area on the East Coast of Massachusetts. Recently new varieties have appeared, that are probably being brought in by barges that pass by on a daily basis from all over the world. Does anyone know of a good data base that compares, list and locates the specific types. I have heard of some people having negative results, but I have had nothing but 100% positive experiences using it in edible gardens for years, but as new varieties appear, I want to make sure I stick with the non-toxic varieties and want to better understand other uses for seaweed in general. Since so many people who have posted here are from all over the world, a way to post photos of the seaweed and descriptions for possible identifications of different varieties and locations they are found would be great to share. Thanks.

    • Sounds like a useful project. We would be happy to post your results in an article on this site. Let us know how it goes. You can contact me directly at

  • John

    I just came across your article and thought I’d add some seaweed to my compost tumbler as an activator. I’m going surf fishing tomorrow morning (I live close to the beach) and now plan to fill a bag with seaweed as a bonus. Thanks for the heads-up on the benefits of seaweed in the garden!

    • Good luck fishing John!

      • John

        Thanks, Greg. The fishing went well, and I walked away from the beach with a nice bag of seaweed which went straight to the compost tumbler. Things should be heating up nicely about now…

  • You can use vegetative material, such a lily pads, and add them to your compost, or directly to developing beds. If using for compost, leaving the gathered material in the sun for a few days to dry out will benefit the composting process. This especially applies to enclosed composters such as drum style compost tumblers where moisture does not evaporate as readily as in an open compost heap.

  • Rebekah Scher

    Fabulous article! Thanks so much for the time, energy and thought you put into this .

  • jt

    Do you think sargassum grass (a kind of floating seaweed which has invaded our coastline in Antigua recently) would be used as you describe above?

    • Sargassum grass would work as a mulch, it’s light and fine textured.

  • Sieglinde Proctor

    A friend and I gathered some seaweed for his garden a few weeks ago, and he washed it and put it down. A couple of days later, the smell was horrific. I asked him later if the seaweed helped his plants, and he couldn’t say one way or another. I have tried seaweed in the past, and I remembered why I stopped using it. The smell is quite distinct. But a lot is being done with very diluted ocean water in this way, and some people are having great results, due to the high minerals in sea water. Dilution 1 cup sea water to 9 cups plain water. Diluting it further may not hurt. Online sites have more information.

    • Sounds like there was something in the seaweed that rotted. We’ve been using seaweed for over 30 years and have not experienced any foul odors. There is a mild smell to fresh seaweed which we find pleasant. After two or three days in the garden sun it dries and shrinks, then is crispy and entirely odorless. After a rain it re-hydrates somewhat, again there is no odor.

  • cliff ingham

    I live in south Florida. Recently a large amount of seaweed washed on the beach near me. I grow my own wheatgrass for juicing and thought that this would make a good media for growing wheatgrass. So I used it to grow my next batch. I was amazed at the results. The grass grew faster. I got about a 30%increase in yield. The juice is much sweeter. This is much easier to work with verses soil. AND its FREE!!!. On my next batch I will use a sea weed tea to water with.

    • Glad to hear of your results. Seaweed is one of the last free deals out there, and such a great resource for gardeners.

  • Timber

    Anyone have experience using seaweed in vermiculture composting systems. anything or critters that might be harmful to worms?

  • We use seaweed directly on the bed in generous amounts. It has been a great addition to the beds.

  • Yes, it’s one additional benefit from seaweed. The chickens love the bugs.

  • NDev

    Loved this, thank you. It is exactly what I have been doing. I am fortunate to live two mins from beach (one way) and two mins from allotment (other way) so have been collecting little bit each day on daily dog walk. It made sense to me for all the reasons you write about. South East coast of Kent, England.

    • Thanks for your comment. We also try to bring up a bucket of seaweed or two per day, it adds up!

  • John Hartin

    Hi Greg, I hope you are still around as this discussion/topic is years old..Just a bit of advice from you please..I have a 1000 litre cube which I added approx 500 litres of water and 500 litres approx of kelp, bubble wrack, razor wrack and sea lettuce. this was back in Nov 2016. Can I use the fermented liquid as a foliar spray and liquid feed on my tomatoes ( poly tunnel ) and potatoes…( both crops blighted in 2016 ) .Lastly do I need to dilute this liquid and if so by how much.. I hope to hear from you in due course…regards John in N. Ireland..

    • Hi John,
      Sounds like an interesting project. Your mix would make a useful liquid feed supplying your soil and plants with minerals and trace elements. This is of course not a complete treatment – you still need to add fertilizer and/or compost, maybe rock phosphate and maybe a soil lightener like peat. (Although you are living in the land of peat, perhaps your soil is naturally light. )
      My suggestion is to use your mix as a foliar spray for tomatoes only if you need it. For minor flea beetle infestations, for example, we use sticky traps and even hand grooming since tomatoes are prone to fungal diseases which are thwarted by keeping the vegetation as dry as possible. Potatoes are in the same family with similar concerns. As a general practice, we try not to wet the foliage of either crop. Your 50/50 mix is probably diluted enough, but I would apply it at the base of plants only, and use the precautionary principle – test it first on a small area.
      We have best results form seaweed when using it as a mulch, since it protects the soil from drying out in the top few inches where most root activity occurs. And the elements are gradually introduced through periodic watering, with the remaining mass incorporating nicely into the soil. Some of our friends rinse the seaweed first with fresh water, we don’t bother and have not seen any problems with this practice.
      Good luck and let me know how it works out.

  • Thanks for your comment Carla. Seaweed is ‘gold’ to the gardener, you’re fortunate to have this resource nearby.

  • norm bo graham

    there was an algae bloom in a NY lake (Fresh water). I raked out a large clump. Worked it into the soil by the road, and planted tomatoes. By the end of the season, I had 6′ tall vines. lol. Fruit production was better then an average plant, but not over the top. Tomato’s tasted like tomato’s.

    • Way to go Norm. Our tomatoes are well mulched with seaweed due to the heat wave, and the plants have never looked better. Seaweed is a great resource!

  • Nicola Mcdonnell

    Wow!… for my master gardening course here in Victoria I chose Seaweed as my discussion subject on mulches. Thanks so much for an extremely informative article about the fantastic uses of seaweed here on the West Coast of Canada. I will never look at another beach of seaweed the same again…fabulous great article and Thanks!

    • Thanks for your comment. Seaweed is a gift for the gardener!

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