Smells Fishy! Seaweed Fertilizer vs Fish Fertilizer – What’s the Difference?

Using the right fertilizers in your garden can be challenging – especially considering there are so many different types on the market.

And two popular products that always receive plenty of buzz around the growing season are seaweed and fish fertilizers.

But what exactly are they? Are they the same thing? What’s the difference?

And how much do they smell?!

In this article, we take a look at seaweed fertilizer vs fish fertilizer, and help you choose the right formula for your yard.

Seaweed and Fish Emulsion – The Short Version

Let’s keep things short and simple for anyone who just needs the abridged summary of this article:

Fish emulsion and seaweed fertilizer are two different things – and should not be confused.

Fish fertilizer can mean fish emulsion, fish meal, and fish hydrolysate – but they are not the same. We’ll explain more about this, below.

garden spatula with fertilizer

Fish fert is used to improve overall soil health, increasing its fertility by adding essential nutrients that plant life needs.

Seaweed fert is also used as a soil conditioner, and it will improve soil texture and water retention, as well as help to reduce the occurrence of pests and disease.

Both options are extremely beneficial to plant life in general and can encourage strong, healthy roots, as well as bright, colorful flowers, and high vegetable yields.

So, which do you choose? Read on to find out!

What is Seaweed Fertilizer?

As you might expect, seaweed fertilizer is made from seaweed.

Thank you, Captain Obvious.

It’s an organic formula that is used to boost soil fertility and plant growth, as seaweed absorbs beneficial nutrients and minerals from the seas and oceans it’s found in.

Living in a tidal environment, seaweed will spend some of its life underwater, as well as the times its drying in the sun. And that is a winning combination for developing plant-boosting goodness.

Sometimes known as kelp (a variety of seaweed), seaweed fertilizer comes in different forms, including concentrated liquid, and dried organic material – which is basically just crushed, ground up seaweed.

Being plant based itself, seaweed fertilizer is seen as a fully organic option, and is becoming more and more popular for use in 100% organic gardening. Follow that link for more tips on growing green!

As a result, you’ll find that most seaweed fertilizers are OMRI listed (Organic Materials Review Institute).

Alternatively, if organic gardening isn’t your thing, check out this article on different types of gardening methods to find your niche.

Seaweed Fertilizer Uses

By benefiting a plant’s overall health, and vigor, seaweed fertilizer can be used pretty much anywhere in the garden – and in your houseplants, too!

It helps to support the thickness of a plant’s cellular wall, which can in turn help to prevent disease. Used just before winter, a seaweed fertilizer can also improve a plant’s resistance to the cold.

lawn in winter

And while we’re on that subject, click this link to find out how you can protect your grass from frost, to help see your lawn through the winter.

Seaweed fertilizer is perfect for use when transplanting, as it reduces transplant shock when moving plants into a new environment.

Seaweed fert can be used to help new seeds germinate. Soak the seeds overnight in a properly diluted solution, or spray them after sowing.

Check out this article on the different types of grass seeds if you’re looking to repair or start a new lawn.

In fact, there isn’t really a situation in the garden that wouldn’t benefit from seaweed fertilizer – given the fact that it’s an all-natural product.

Just be aware it’s not a magic bullet, and you will need to use other sources of nutrients, particularly when you need to boost nitrogen and phosphorus levels.

And it is still possible to burn plants with this type of product – especially if you incorrectly dispense a commercially available liquid seaweed concentrate.

Seaweed Fertilizer Advantages

  • A major plus point in the seaweed column is the fact that it is a sustainable resource, and doesn’t harm the environment.
  • It’s available in liquid and granular/dry forms – which increases your application options, with a more versatile product.
  • Contains a healthy dose of growth hormones – perfect for boosting anything green in your yard.
  • Contains anti-stress compounds – to help plants through times of trouble (which we could all do with from time to time)!
  • Seaweed fertilizers release their goodness over time, so plants will have a steady boost of nutrients over several months – rather than all at once.
  • Using seaweed fertilizers can improve the efficiency of a plant’s nutrient uptake, and can be applied both into the soil and effectively to the leaves.
  • Doesn’t harm other helpful organisms.
  • Seaweed fert contains a good dose of phosphorus, which is known for helping vegetable yields and promoting healthy fruit growth.

Seaweed Fertilizer Disadvantages

  • Thanks to the fact that seaweed fert is organic, it has very few downsides – and although some products will still have a bit of a pong.
  • However, seaweed will have a high salt content, and this can be detrimental to plants in your garden (although it will dilute/wash away with watering and/or rainfall.
  • Seaweed fertilizers (and organic ferts in general) are slower acting than their synthetic counterparts – if you’re looking for a quick-fix – this isn’t it!

What is Fish Fertilizer?

To many new green thumbs, the thought of adding fish-related products to the garden might be a little perplexing, at first!

Yet the remains of our aquatic friends contain loads of nutrients and minerals that they’ve absorbed during a life in the sea.

And it’s these nutrients and minerals that we want, as they can be highly beneficial to the plant life in our yards.

But what is a fish fertilizer actually made from?

If you’re eating, I apologize!

lawn fertilizer in bag

Fish fertilizers are organic formulas that are most commonly available in a concentrated liquid form,  although there are dry feeds available – such as fish meal.

This is derived from a process that prevents usable fish products from going to waste, and there are three, main types.

Fish Emulsion

This type of fish fert is created by cooking fish carcasses at high temperatures, and then grinding them into a paste, which includes the scales, skin, guts, and bones.

The oils are then removed – and used for other industries – such as health and beauty products.

Sulphuric acid might be added to balance out the pH levels.

This fishy sludge is then strained, and the liquid that remains is called “fish emulsion.” If you think the bottle smells bad, imagine how it is at the processing plant!

Fish Hydrolysate

Imagine the above process but without the oils removed. Fish hydrolysate is just pure, 100% fish waste, cooked and ground into a concentrated liquid.

While it’s usually more expensive than emulsion, it’s much more beneficial to your plants, as it doesn’t remove all the extra goodness contained in the fish oil.

Fish Meal

Basically, fish meal is what’s leftover from fish oil production – grinding and cooking the fish, and drying and pressing the meat and bones. It makes an excellent soil amendment, and is easily composted.

Fish meal also doesn’t smell nearly as bad as liquid fish fertilizers – so this might be an option if you really can’t stand the odor.

This article on liquid vs granular fertilizers is highly recommended if you’re struggling with choosing between dry and wet products.

A quick word on the environmental impact of fish fertilizers. It is thought that some products are made from fish that have been specifically caught for this purpose.

This is grossly irresponsible. If you suspect a fish fertilizer to be using anything other than leftover fish waste, please, purchase another, more eco-friendly product.

And speaking of eco-friendly, this article on nature-approved lawn care is a good place to start for going green; but you might not want a patch of grass at all after you’ve read the history of lawns!

Fish Fertilizer Uses

A good, responsibly sourced fish fertilizer can be used just about anywhere in your garden – your plants are going to love it!

The beauty of these organic fertilizers is that they contain a lot of micronutrients, such as sodium, calcium, magnesium, sulfur, and chlorine.

Plants need a total of 17 different nutrients to really thrive, and not just the “big three” NPK numbers (nitrogen (N), phosphorus (P), and potassium (K)).

a green lawn in backyard

That said, nitrogen is the most important of these, and fish fertilizer happens to have a lot of it, because fish are high in protein. It also has phosphorus and potassium elements, too.

Use a fish fertilizer on your lawn in the early spring – and you’ll see the benefits by the time BBQ season comes around!

Fish Fertilizer Advantages

  • Providing it’s properly stored, fish fertilizer has an indefinite use-by date – but needs to be used as soon as possible once it’s been diluted.
  • Used correctly, concentrated fish emulsion is going to last you a long time. You don’t need much of it to treat a wide area, once diluted with water.
  • High in nitrogen, fish fertilizer is excellent for boosting a plant’s chlorophyll, improving its ability to photosynthesize.
  • Fish fertilizer is a time-release formula, which is perfect for feeding plants over an extended period.
  • Ideal for leafy green vegetables.
  • Adds healthy microbes to the soil as the product is broken down by organisms, such as earthworms. Which means it also doesn’t kill helpful bugs and insects!
  • Works great as part of your compost pile. Add some into your tumbler and jump start your production of the black gold.
  • Don’t worry about the smell too much – it disappears after a day or two!

Fish Fertilizer Disadvantages

  • There’s no doubt about it, the major downside of using a fish-based fertilizer is the odor. Some of these products can smell pretty bad! (Although low-odor options are available).
  • Some products use fish specifically harvested for this purpose – which is extremely impactful on the environment and should be avoided at all costs.
  • Like seaweed fertilizer, fish fert is a slow-release formula, which isn’t going to be beneficial if you’re looking for fast results.
  • There are reports that some fish fertilizers might impair the taste of some vegetables.
  • It’s very easy to “burn” plants if you’re over-zealous with a fish fertilizer application. Take care you have your quantities right to avoid this.

If you do happen to overuse any kind of fertilizer, this article on how to reverse lawn fertilizer burn might be able to help.

When to Use Fish/Seaweed Fertilizers

The beauty of these two products is that it doesn’t have to be an either-or conundrum.

Used simultaneously, your garden will reap the benefits from both types of fertilizer. You can even purchase liquid seaweed and fish emulsion products that already combine the two.

I would suggest trying a seaweed fertilizer on your flowers and veggies, and a fish fertilizer as part of your lawn care schedule. Don’t miss our month-by-month guide to lawn maintenance while you’re here!

Both options are best applied when plants are actively growing. Take a look at the video below which shows the results of a fish and seaweed fertilizer application.

And for a catch-all guide to feeding the plant life in your yard, head over to this article that fully explains when and how often you should fertilize your garden.

Other Types of Fertilizers

Of course, there are many more different types of lawn fertilizers out there to give your lawn the much-needed boost it deserves.

Follow the link above for a full article on what’s available.

Alternatively, you might also be tempted to make your own, which can also be used in other areas of your garden – such as flower beds and vegetable patches.

Check out this article on DIY fertilizers, and pay particular attention to the organic “compost tea” recipe!

And read on to find out if you can make your own fish fertilizer, too.


How do you make fish waste fertilizer?

Like many DIY fertilizers, there are several recipes/methods available when it comes to making your own fish-based product at home.

It also takes a bit of time, and effort on your part, and while it can save you money in the long run, it can be a laborious – and extremely smelly – process.

Still, if you’d like to give it a go, watching this video is the perfect way to get started.

Can you use seaweed fertilizer on indoor plants?

Yes! Seaweed fert is excellent for indoor plants – but you need to make sure you have your quantities right when mixing liquids.

A rule of thumb is one teaspoon of product to one gallon of water – but always double-check the instructions to be sure.

Does fertilizer have a shelf life?

As mentioned above, many of these products can be used indefinitely (five to ten years), providing they haven’t been opened/diluted.

This article on fertilizer shelf life will tell you more – but just make sure to always read the label.


There is a distinct difference between these two products, but when it comes to seaweed fertilizer vs fish fertilizer – which is the best?

There isn’t a clear winner, as they both have different uses for helping boost the plant life in your yard.

(Although if it’s a choice between the two, I’d go with seaweed fert every single time!)

Let me know which option you prefer, or if you have any fish/seaweed fertilizer tips and/or experience you’d like to share with the community.

Stay safe out there, and happy gardening!

Andy Gibson

My name's Gibson. Andy Gibson. I like to think of myself as the Bond of the backyard, that is if yard work ever became sexy. I write about everything about indoor and outdoor gardening and the dread-it-but-still-need-to-do-it chores around the yard, like cleaning out the gutter guards.

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