By Luke Sumpter Reviewed by: Silvia Maroto


Achieving a good crop of cannabis means giving your plants the best life you can. From pH levels to moisture, nutrients, beneficial bacteria, and more, there’s a lot to think about when it comes to growing weed. If only there was a single thing that could help in all of these respects.

Well, there is: seaweed! Or, kelp, more specifically. This marine organism is absolutely bursting with nutrients, and can help to maintain an environment in which your cannabis plants can grow and thrive. Discover all about seaweed, and how to use it, below.

What Is Seaweed and Where Does It Come From?

Seaweed is the generic name given to over 10,000 species of algae—more specifically, “macroalgae”—that live in the sea. These non-vascular organisms live on a combination of sunlight, nutrients absorbed from the water, and carbon dioxide. As they are non-vascular, they cannot transport nutrients around their bodies, and so many remain mostly submerged in order to survive.

Seaweed can range from very small to huge. In the case of Antarctic kelp, it can reach 33 metres in length! Each species has its own look, flavour, composition, and nutritional value. In this article, we’ll be focusing on kelp.

What's the Difference Between Kelp and Seaweed?

Kelp is a subspecies of seaweed that is particularly nutritious. It forms in so-called kelp forests and grows in shallow, nutrient-rich waters. It’s this environment that makes kelp so beneficial to cannabis and other plants. The seaweed absorbs a vast array of ocean minerals, which are then dispersed into the soil when used as a fertiliser.

In terms of nutrient content, it’s really quite incredible. Overall, kelp contains over 60 trace elements essential to cannabis growth. These include iron, manganese, cobalt, zinc, and molybdenum—all of which are greatly beneficial to plants.

What Are the Benefits of Using Seaweed for Cannabis?

But there’s much more to it than that. Below, we outline the pros and cons of using kelp to grow cannabis.

Pros

Contains over 60 trace elements essential to the healthy development of cannabis plants Stimulates the growth of beneficial microorganisms in the soil
Helps to maintain a proper pH level Kelp mulch regulates the moisture content of the soil
Kelp foliar spray delivers a rapid hit of beneficial nutrients Powder can be mixed into soil before a grow begins to create a very fertile growing environment

Cons

Can be illegal to harvest in certain places
Might be difficult to get hold of if you don’t live near the coast
Other than that, kelp is a pretty good choice!

Pros

Contains over 60 trace elements essential to the healthy development of cannabis plants

Stimulates the growth of beneficial microorganisms in the soil

Helps to maintain a proper pH level

Kelp mulch regulates the moisture content of the soil

Kelp foliar spray delivers a rapid hit of beneficial nutrients

Powder can be mixed into soil before a grow begins to create a very fertile growing environment

Cons

Can be illegal to harvest in certain places

Might be difficult to get hold of if you don’t live near the coast

Other than that, kelp is a pretty good choice!

How to Use Kelp in Your Cannabis Garden

Using kelp to grow cannabis is pretty easy, and there are a few different methods of administration, which means that you can tailor your use of kelp to specific ends.

Different Forms of Kelp

While you can just throw some harvested kelp onto your soil and let it break down, there are several options to choose from when it comes to using seaweed to grow cannabis.

Kelp Food

Kelp food, or kelp meal, can be mixed directly with soil. This must be done around four months before you intend to germinate seeds. This method supercharges the growing medium and creates an incredible environment for your plants to flourish.

As well as being packed with nutrients, after several months, the soil will develop a thriving ecosystem of beneficial bacteria, all of which will help to keep your plant healthy throughout its life cycle. Plus, the pH balance of your soil should be correct from the very beginning.

To use kelp meal, add around 0.5kg of kelp food per 9m³ of soil, and leave for at least four months.

Why Seaweed Is a Superfood for Cannabis Plants

Kelp Powder Foliar Spray

Kelp powder must be mixed with liquid to make a seaweed solution. This foliar spray provides perhaps the most direct means of getting all the goodness of kelp into your cannabis plants. Simply spray it onto the leaves and they will absorb it, transporting it immediately around the plant.

It’s worth noting, though, that using a foliar spray isn’t a viable regular feeding method. It’s fantastic at providing a large dose of nutrients to a plant that needs it, but it shouldn’t replace a good feeding regimen via the growing medium.

To make a kelp solution, mix ½ a teaspoon of kelp powder with 5 litres of water and apply via a mist.

Why Seaweed Is a Superfood for Cannabis Plants

Mulching

Mulching is another great option for using seaweed with cannabis. To mulch, you’ll need a supply of fresh and whole kelp in its natural form. Once acquired, simply pile it around the base of the plant and leave it to decay. As it breaks down, its nutrient-rich body will pass down into the soil, where the plant’s roots will be able to absorb it. Moreover, as it breaks down gradually, it will continue to feed your plant until it’s all disappeared.

Aside from the above, mulching also prevents invasive plant growth, encourages the growth of healthy bacteria in the soil, retains moisture in the soil, and helps to maintain the correct pH balance.

Why Seaweed Is a Superfood for Cannabis Plants

Composting

Alternatively, you could add fresh kelp to the compost and allow its nutrients to mingle with and enhance those of the general compost heap. If you choose to go this route, mix the kelp well with the contents of the compost bin, as it could otherwise prevent good airflow and lead to improper decay.

Why Seaweed Is a Superfood for Cannabis Plants

Liquid Fertiliser

Another very easy option is to use a kelp-based liquid fertiliser to feed your cannabis plants. Administering kelp liquid fertiliser is just like doing so with any other liquid fertiliser. You simply add the required amount to water, and give it to your plants.

Although it differs from product to product, around 1 teaspoon per 2.5 litres of water is likely sufficient when using a liquid kelp fertiliser. Don’t be tempted to overdo it, though, as this will have negative consequences!

Why Seaweed Is a Superfood for Cannabis Plants

How to Forage for Kelp

It’s pretty easy to buy seaweed fertiliser, powder, and meal online or in garden centres. However, if you live by the sea, you might also be able to forage for your own.

You’ll find kelp strewn across the shoreline when the tide goes out, and you can just pick it up and take it home. Double-check local laws before you do this, as in some places it may be illegal. Likewise, remember that other organisms thrive in kelp too, so don’t remove all the kelp from a beach, as you risk damaging the local ecosystem.

Kelp and Cannabis: Is It Worth It?

Yes, definitely. The only time that going without kelp might be worth it is if it’s hard to get hold of. But in most cases, buying it shouldn’t be a problem, and finding it should be fairly easy too, depending on where you live.

Seaweed is perhaps the most nutrient-rich fertiliser available for growing cannabis, and that’s not to mention its many other benefits as well. If you’re able to use kelp in your cannabis grow operation, then you should do it!

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