Liquid Seaweed Fertilizer


1 Quart

Canadians can get it here

Plants have to deal with a lot of environmental stress.

This includes heat, cold, wind, drought and disease.

That’s where liquid seaweed fertilizer comes in.

Seaweed for plants has been used by gardeners and farmers for thousands of years.

People have collected it off the beach and put it right on their gardens as a seaweed fertilizer diy and mulch that quickly broke down, releasing dozens of minerals and vitamins and other beneficial components.

When I lived near the ocean on the west coast, I would drive to a nearby beach to do the same.

But nowadays I use liquid seaweed fertilizers instead, made from one of the most common seaweeds: kelp.

Kelp is a wonderful soil amendment, but when we don’t have it around, a seaweed liquid fertilizer still brings many of the same benefits.

And a big advantage of these liquids over the solids is that we can spray them onto plant leaves for direct leaf uptake.

When you do that, the plants get a nice shot of dozens and dozens of different minerals and vitamins.

But the main benefit of liquid seaweed is the natural plant growth regulators and hormones it contains that help plants grow faster, healthier and stronger.

And one of the main things they do is help plants deal with those environmental stressors.

Benefits Of Liquid Seaweed Fertilizer

Big Watermelon With Liquid Kelp Fertilizer
These record-breaking watermelon were grown with my liquid seaweed fertiliser and liquid fish.

Probably the most important of seaweed fertilizer benefits is that it’s the best when it comes to boosting plant health and helping plants deal with environmental stressors such as heat, cold, wind, drought and disease.

Like all of my organic fertilizers, it can have a big impact on boosting plant growth, but I often think of it as really excelling at promoting healthier plants.

Using seaweed as fertilizer also increases overall nutrition, including protein content (the protein content of our crops has dropped considerably since WWII).

Seaweed feed has been well studied and has become a mainstay of organic farming and gardening. T. L. Senn did a lot of research on using seaweed as a fertilizer back in the day. He eventually wrote a great little book called ‘Seaweed and Plant Growth.’

His research showed not only the kelp fertilizer benefits for plant health and growth, but also that a quality liquid seaweed can help control insect pests such as spider mites.

Who Needs This The Most?

The reason I recommend this to everyone is that it really is helpful in most gardens.

It doesn’t necessarily give the big boost in plant growth that some products give, but it does boost plant health, which helps discourage pests.

It’s just a nice piece of preventative health care to bring into the mix, and at times can be a quick cure for various ailments a plant may encounter.

That’s why organic farming consultants often recommend it be included in any spray application regardless of what else is being used.

Seaweed Fertilizer Make Your Own

How to make seaweed fertilizer: if you live near a beach with some seaweed on it, you can just take that and use it directly as a seaweed garden mulch, provided it’s legal in your area to remove it.

Be sure to leave some for the beach, though, as it has a big role to play there as food and habitat for many different species.

Or if you want to make a basic liquid seaweed fertilizer, pack the seaweed into an airtight container and fill it with water.

You don’t have to rinse off the salt first.

Let it sit for at least a couple of weeks (or more like a couple of months in cold weather).

It smells quite bad because it’s an anaerobic fermentation, but that’s okay. Adding a bit of EM into the water can cut down on that.

When you’re ready, mix it with 10 parts water and spray it directly onto your plants. It’s not as concentrated as a professionally manufactured kelp fertiliser but will still have many benefits.

If you let it sit long enough, the seaweed will probably decompose and dissolve, but if there’s any left, you can still throw it onto your garden as a mulch.

Finding A Quality Liquid Kelp Fertilizer

Seaweed Fertilizer From The Ocean
Some seaweeds can grow over 2 feet per day.

There are several species of seaweed that are commonly used for fertilizer.

There are debates as to which one is best, but the similarities are far more important than the differences, so when you’re looking for a seaweed garden fertilizer, my view is to not worry too much about the species.

What’s more important is that the kelp plant food is processed without heat and high pressure, so as to keep as many of the beneficial components intact.

Even some of the organic products – like the popular Maxicrop liquid seaweed – are processed in such a way that they don’t retain nearly as many of the natural growth regulators and beneficial microbes. That’s not to say products like that wouldn’t have any benefit, but they’re definitely not the same quality.

The other thing to think about is whether the manufacturer is sustainably harvesting the seaweed, because overharvesting is becoming an issue. That can be more difficult to figure out.

What I do is contact the manufacturer to ask what they’re doing to make sure their process is sustainable. If they have a good answer instead of brushing me off, that’s a good start. Then I go to the internet to see if anyone else has any more info on the company.

I would like more solid info that that, but seaweed harvesting is not an issue under public scrutiny at this point, even by environmental organizations, so I mostly have to go by word of mouth.

The liquid seaweed fertilizer I use is from Neptune’s Harvest, cold processed and organic. I did some digging and found that it’s made by Thorvin, one of the best seaweed manufacturers in the world when it comes to quality and sustainability.

In terms of quality, they dry the seaweed at low temperatures using geothermal energy in order to retain the nutrients and preserve bioavailability.

In terms of sustainability, they harvest in a geographically remote location, in very clean water, away from agricultural run-off and commercial shipping. They also rotate harvests to allow for sufficient regenerative growth.

How To Use Seaweed Fertilizer

Shake well before each use. Once you’ve mixed with water, use it the same day.

Here are their recommended application rates:

  • House Plants: Use 1 tablespoon per gallon of water every 1-2 weeks.
  • Outdoors: Use 2 Tbsp per gallon of water every 1-2 weeks.
  • Lawns: Use 1 gallon for 8000 sq ft every month.
  • Seeds: Use 1 teaspoon per cup of water for soaking seeds.

They suggest applying until the soil is saturated or as a foliar feed in the morning or evening until the leaves are wet.

That may be enough for you but it doesn’t really tell you how much to apply overall, so I’ve also dug into their agriculture recommendations to see if I could find a little more detail.

They recommend 3 gallons of product per acre, 4 times per year. That works out to about 1 quart per 1000 square feet per year, so that’s what I aim for.

In my garden, I use 1/2 cup of liquid seaweed fertilizer per 1000 square feet every month for 8 months of the year.

I suggest mixing it with at least 50 times as much water, which would be 1.5 gallons for 1/2 cup of seaweed. Or just set a hose-end sprayer to spray 5 Tbsp per gallon.

Liquid seaweed is great mixed with my other fertilizers and microbial inoculants.

When soaking seeds, you can mix in an equal amount of sea minerals fertilizer or liquid fish fertilizer. So that would be 1 teaspoon of seaweed (and perhaps 1 teaspoon of sea minerals or fish) per cup of water.

You Can Get It Here


1 Quart

In summary, this liquid seaweed fertilizer:

  • Provides many benefits, but is especially known for improving plant health and helping plants deal with heat, cold, wind, drought and disease.
  • Is manufactured sustainably, without heat and pressure, therefore providing much more benefit than other brands.
  • Is organic (OMRI-Listed) and undoubtedly one of the most popular organic fertilizers available.

As a free bonus when you order today, I’ll also enroll you in my online Biostimulants course.

Just choose your container size and click ‘Add To Cart’ up above!


  • I ship in the U.S. only. I ship 7 days a week.
  • In the continental U.S., shipping is $10 (if your order is $99 or less) or free (if your order is $100 or more).
  • All of my products have a 1 year 100% money-back guarantee.
  • If you have a question about a product, leave it in the comment section below I'll try to respond within a few hours.
  • Dry fertilizers and compost tea brewers ship separately so they will arrive on their own maybe a day or 2 apart from my other products.
  • With every order, I send $1 to Organics 4 Orphans and other similar organizations. O4O is working with the world’s poor to help them grow organic, highly nutritious, highly medicinal food for themselves, and then use the surplus food to generate income for themselves as well as feeding the orphans in their communities. My hope this year is to again send $1500US, which is enough to start projects in 25 new communities!

Free $25 Bonus When You Buy Today

When you buy this liquid seaweed fertilizer, you get enrolled in my online Biostimulants course.

The course includes 10 videos totaling about 75 minutes where I chat about seaweed, fish, sea minerals, molasses, rock dust, and how to use them all.


  1. MagToby on May 22, 2015 at 10:11 pm

    Early this morning, I sprayed my zucchini with this liquid seaweed, sprayer set at 5T per gallon. Now the leaves look damaged. The edges look spotted and slightly wilted. They looked great before. Is this common? Did I miss a directions?

    • Phil on May 22, 2015 at 10:33 pm

      Hmmm, I’ve seen some damage with the fish before – never with the seaweed. On the bottle they say to mix it 1:128, which is more like 2Tbsp per gallon of water, but on their website when I look at the application procedure in more detail, they often say 1:10, which is like 25Tbsp per gallon of water. I’ve always done 5Tbsp with no problems, although it never hurts to use more water. I’m very sorry for your troubles Elizabeth. Zucchini leaves are pretty tough – I bet they’ll recover soon.

      • MagToby on May 23, 2015 at 1:02 am

        Thanks, Phil. I am optimistic. I’ll let you know what develops. 🙂

        • tpc4545 on August 29, 2015 at 6:55 pm

          Well what happened, Elizabeth?

          • MagToby on August 30, 2015 at 2:37 am

            The leaves developed symetrical markings which persisted, but the plants looked wonderful in posture, seemed really happy. Things went fine from there. Wish the season weren’t ending soon.

  2. aamir raza on October 15, 2016 at 11:02 pm

    is it possible that after applying neptune 2-3-2 or 2-1-3 i do not remember that for the first two or three days the plants do not look good the flowers that were there seem dried up,the leaves also not appear too strong but a couple of days later things start looking up and eventually more than they were before it us happening now rose mums hawthorne jasmine basil are looking weak started application two or three days ago could you help thanks

    • Phil on October 25, 2016 at 5:35 pm

      It could be if you didn’t dilute it enough. Dilute at least 50 times (at least 1 gallon of water for 5 Tbsp of neptune’s harvest.

  3. James McCarthy on February 12, 2017 at 9:07 pm

    What should I use for a soil that has virtually no Nitrogen and very little Phosphorous?

  4. Jason on March 22, 2017 at 1:09 pm

    I live in Wisconsin so I can’t harvest fresh seaweed. What is the best Kelp/Seaweed you can purchase online? Thanks for any info. I know Neptune is ok but are there better options?

    • Phil on March 22, 2017 at 1:12 pm

      I’d say the best overall value is Neptune’s Harvest, which is why I’m selling it on this page. They’re using Thorvin seaweed, which is one of the best in the world.

  5. Olwyn Rutter on February 9, 2018 at 4:16 pm

    Hello there,
    This is hilarious. I have just moved from Victoria, BC and now live on Crete Greece. Trying desperately to find a source of orgnic liquid seaweed fertilizer. Don’t suppose you ship to Greece do you? If so, what would the cost be? The product I am looking for is to be used on organic hydroponic vegetables. I wish I had left all my clothes out of my cases and just brought gardening supplies instead!
    Look forward to hearing from you.

    • Phil on February 12, 2018 at 9:28 am

      Sorry Olwyn, I can’t ship overseas. There must be someone in Europe who can help.

  6. Ben on February 18, 2018 at 7:04 am

    Curious how often you spray your plants in particular vegetables.

    • Phil on February 23, 2018 at 9:01 am

      I do everything monthly, which is great, although I would do weekly in very small amounts if I had the time.

      • Jerry Foster on June 22, 2019 at 11:27 am

        Is there a high temp when it’s not good to spray the sea weed,I live in Florida.

        • Phil on June 23, 2019 at 5:18 pm

          I’ve never come across anything about this, other than that it’s best to apply in the morning when it’s not quite as hot. Plants still need nutrients when it’s hot, though. Sorry I can’t give you more specific info on temps.

  7. Md Moniruzzaman on July 29, 2018 at 1:08 am

    I use organic wow soluble kelp powder. Is it different than liquid seaweed? Which is more beneficial liquid seaweed or powder seaweed?

    • Phil on August 2, 2018 at 8:27 am

      It’s different but they’re both good. I use liquid because it’s ready to use and also because it’s made with fresh kelp instead of powdered kelp. But the powdered is still beneficial. I’ve never seen any research comparing the two.

      • Md Moniruzzaman on August 3, 2018 at 11:38 pm

        Thank you for the prompt reply. I’m interested to use both and check myself which makes difference.

  8. Adrienne on January 21, 2019 at 10:45 am

    Could this be used on house plants? If so, what would be the proportions to dilute? Thank you – Adrienne

    • Phil on January 29, 2019 at 7:23 pm

      Absolutely. For houseplants, use 1 tablespoon per gallon of water every 1-2 weeks.

  9. Cassidy on May 8, 2019 at 8:42 am

    Can you use this to spray leaves that will be harvested, I.e., lettuce p, spinach, etc. does it change the flavor?

    • Phil on May 12, 2019 at 12:09 pm

      The dilution is such that I’ve never noticed a thing, and I tend to spray up until close to harvest time.

  10. Mark on May 24, 2019 at 1:45 pm

    Kelp does have hormones that make it grow 2 to 3 feet a day. Transferring hormones from one plant to another plant, Does it really Work?
    Maybe its not the hormone in kelp that is making your plants grow bigger? Maybe it is the vitamins and nutrients that are making plants grow bigger? I am doing an experiment on several different plants tomato, cucumber, melons, herbs and few flowers. Half plants with vitamins and half plants without vitamins, with all same soil, inoculated with mycorrhizae before placed in pots/planters. Have been feeding my plants multivitamins every time i water them (1 multivitamin per gallon of water totally dissolved). The plants that i been feeding vitamins are double the size than ones i have not fed vitamins. If there is any deficiency in my plants i’ll feed them very little fertilizer just make sure plants are as healthy as they can be for my experiment. Kelp is loaded with vitamins/nutrients. Before i become a true believer that the hormones is making plants grow bigger i would have see the results with just the hormone itself without vitamins/nutrients kelp produces.

    • Phil on June 1, 2019 at 10:55 am

      Thanks for sharing, Mark. I think you’re right that the nutrients are part of the picture. But in many of the great books on using seaweed as a fertilizer (which you can find online from Acres U.S.A.), they really stress the hormones, not that the hormones gets “transferred” to the plants – just that they influence plant growth, which we know for sure. Perhaps it’s hormones and nutrients. Sounds like a great experiment you’re doing!

  11. Dee on June 27, 2019 at 7:09 pm

    3 Qs re: fertilizing to get an Overview of how to best view & do fertilizing when using the Natural Big 4 inputs you advise. Kelp — Sea Minerals — Fish Fertilizer – Compost Tea/BioAg.

    1. Do they provide everything your garden will need with respect to fertilizing (once the soil structure & minerals have been balanced)? Is there any reason to “additionally” give your plants an “all around organic based fertilizer” such as retail OMRI organic products that are labeled as General Garden Fertilizers, that have things like alfalfa, feather, fish bone? In otherwords, is it possible to ONLY use the “Big 4” and have an excellent garden without the added expense and work of additional products? (I realize these Big 4 are “food” for the microbes and not the plant directly).

    2. Do these 4 products actually correct an imbalanced “soil” so if you are not sure of your soil balance — over time using these Big 4 will bring it naturally into balance?

    3. I find it very useful to not just “follow” directions but to understand the “WHY”. So with that knowledge it allows me to apply wisely with intent and be able to explore when things go haywire. You have done wonderful work in this blog (& lessons) providing so much of that. If you have the time, would really like to know for each of these 4: Kelp, Sea Minerals, Fish Fertilizer, Compost Tea/BioAg – what is it that they mainly contribute and importantly can they be over applied – i.e. the benefits & their general parameters? For example, I’ve heard Fish Fertilizer is primarily for Nitrogen for green color & growth of foilage and there is no concern of it being over applied. It would help with the confusion to have a “brief” coherent overview to better understand the “parts” when gardening with natural products to use them properly and bring them all together successfully.

    Thank you.

    • Phil on July 2, 2019 at 8:42 am

      1. The big 4 will get you part of the way there, but not all the way. But I wouldn’t add an “all around organic based fertilizer”. If I were wanting to go further, I would soil test and then add the specific nutrients in which I was deficient. That said, there are other useful products out there. For example, if you soil test with Crop Services International, they’ll usually recommend an additional 1 or 2 microbial inoculants that they have and an additional 1 or 2 micronutrient fertilizers. There are thousands of products out there so there are bound to be other useful ones.

      2. No, they won’t correct soil imbalances much at all. They just make sure your microbes and plants have a little of everything, which is helpful, but the soil imbalances will still be a limiting factor.

      3. On the right side of this page (or the bottom if you’re on mobile), you can read a little explanation I wrote titled “Sea Minerals Vs Seaweed Fertilizer Vs Fish Fertilizer” where I do my best to share the differences. In the end, those 3 are quite similar, just all with slightly different make-ups, and I imagine my explanation probably isn’t enough for you. There are books from Acres U.S.A., especially ‘Fertility From The Ocean Deep’ and ‘Food Power From The Sea’ that may give you some more info. I expect they all could be overapplied but I’ve never tried 🙂 And if you go to the compost tea page, you can read (on the right side) the box titled “Compost Tea Vs SCD/EM Vs Mycorrhizal Fungi” where I make a similar comparison. You can overapply BioAg but not compost tea, although I don’t really have a good explanation as to why.

  12. Annie on March 24, 2020 at 3:56 pm

    Hi Phil,

    I started using the liquid seaweed fertilizer a few weeks ago on my houseplants , and now I am noticing some small mushrooms growing in their soil, and some fungus gnats! Could these be related? I haven’t changed the frequency of the watering.

    Do you have any tips on this? Thanks.

    • Phil on March 25, 2020 at 8:51 pm

      Hmm, that’s surprising. I suppose it could have something to do with the seaweed but I’m not sure what. Mushrooms fruit when they’re ready to. I’d be surprised if the seaweed would stimulate fruiting but perhaps. Mushrooms aren’t generally bad, though, so probably no worries. The fungus gnats are bad, though, and again, I’d be surprised if the seaweed encouraged them, whereas I wouldn’t be surprised if seaweed actually discouraged them. I recommend you stop the seaweed for a month to see what happens, and then start again to see what happens. Personally, I’m using it twice a week on my indoor lettuces right now and they’re loving it 🙂

      • Annie on April 5, 2020 at 5:03 pm

        Thanks, Phil. I’m going to follow your advice and pause for a bit on the seaweed

  13. Judy on May 1, 2020 at 4:22 pm

    Hi Phil,
    Is the blackstrap molasses you sell, organic?

    • Phil on May 1, 2020 at 5:05 pm

      It used to be, but no, not the one I carry right now. It’s non-gmo and unsulfured but not organic.

  14. mary huggins on September 5, 2020 at 10:33 am

    love the product. we’ve been using it regularly since we got it. not much happened at first and then we had a rain and the flower are abundant. one question i have is the when we bought the plant i thought the flowers would be purple. they are not. they are white. is there something we can do to make them purple? i know we add a product for hydrangeas to be blue…so just wondering. thanks

    • Phil on September 12, 2020 at 10:45 am

      I’m not sure which type of plant you’re referring to but almost all flower colors can’t be changed.

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