Earthworm castings in growing marijuana

One of the best ways to ensure a bountiful marijuana harvest is to use earthworm castings on the soil.

This natural material is the by-product of the food digested by the worms.

As such, it is purely organic and extremely rich in both the main nutrients and trace minerals that are essential to the plants.

The benefits of using worm castings

Interestingly, the benefits of using worm castings are not only limited to nutrients.

It has several other surprising advantages, making it deserve to earn the title of super plant food.

For this reason, it is the most popular fertilizer that many big city millennials use to nourish their plants.

While many growers commonly associate composting with hard work, using this method is relatively easy.

Basically, all we need is a good environment for the worms and plenty of food supply to work their magic. Once we apply it to our crop, expect to see it grow healthier and produce richer buds.

Download my free marijuana grow bible to know more about earthworm castings and other ways to nourish your soil.

To get started in using worm castings, it is best to know the basics about it. Hence, this article will cover its benefits, production, and usage.

Because of its tremendous positive effects on the plants, learning about it can be extremely valuable to cannabis growers.

What we need to know about worm castings

Again, the best way to supercharge the soil is to use worm castings. But how do we get started with this method?

For interested growers, this section will provide all the necessary information to start using it effectively in the garden. But first, let’s take a quick look at its composition and benefits.

1. What is it?

As mentioned, worm castings are the excrements of worms from digesting various food scraps.

Somehow, through their digestion process, they produce this material that is loaded with rich nutrients for the soil.

1.1 Worm castings vs vermicomposts

Worm castings slightly differ with vermicomposts when it comes to composition.

Worm castings vs vermicomposts
Worm castings vs vermicomposts

While the former is made purely of worm feces, the latter is a mix of the castings and other materials in the compost.

Both have the same basic ingredient and are often combined with each other. Thus, many growers use these terms interchangeably.

1.2 What kind of worms can we use?

There are specific earthworms that growers use for this purpose.

Growing marijuana using red worm castings
Growing marijuana using red worm castings

The two main types are the Lubricus rubellis and the Eisenia foetida which are also the ones we use as fish baits.

Casually, they are known as the red worms, red wrigglers, tiger worms, and the manure worms.

2. What are its benefits?

Aside from being totally chemical-free and inexpensive, using worm castings can make huge improvements to the garden.

In addition, they are readily available and are easy to make. So, what more do we need?

To truly appreciate their magic, let’s examine how they are beneficial to the crop.

2.1 Aerate the soil

While most gardeners keep their worms in a container, some are more practical and just let them loose in the garden.

Aerate the Soil
Aerate the soil – Image powered by

This allows the worms to perform their most obvious functions which are to tunnel through the soil and introduce oxygen in the process.

As a result, the roots get enough space to absorb more water and nutrients.

2.2 Environment-friendly

Aside from being nature’s decomposers, worms also help households reduce their waste by recycling their kitchen scraps.

Environment friendly

This significantly reduces landfills while enriching the soil and produce bountiful harvests. Add to that, using castings eliminates the need to use harmful chemicals in the garden.

2.3 Get rid of harmful microorganisms

Worm castings release substances in the humus that eliminates toxic fungi and bacteria.

How to make average soil better
Get rid of harmful microorganisms

In effect, they fight off diseases that could possibly weaken the plants and affect our yield.

Moreover, they also introduce good microorganisms that help make the soil richer and the plants healthier.

2.4 Make the soil more absorbent

watering a cannabis plant on a pot
Make the soil more absorbent

The castings can make the soil absorb moisture more easily. As a result, the soil gets all the water that it needs, keeping the plants well-hydrated and at no risk from completely drying out.

2.5 Stabilize the pH of the soil

The soil needs to have a balanced pH to absorb the essential minerals. When we apply the worm castings, this immediately corrects any imbalances in the pH level.

How To Measure PH And PPM For Your Marijuana Grow
Stabilize the pH of the soil

Hence, for many growers, this is the best remedy and preventive measure for nutrient problems.

2.6 Teeming with nutrients

Compared to the ordinary potting mix, castings have ten times more nutrients.

In fact, they contain over 60 micronutrients and other essential elements including nitrogen, phosphates, and calcium.

Teeming with nutrients
Teeming with nutrients

Even better is that unlike commercial fertilizers, they are released slowly in the soil, preventing any nutrient burn or mineral buildup.

2.7 Remove toxins in the soil

Sometimes, there are heavy metals and other toxic matter in the soil.

Remove Toxins in the Soil
Remove toxins in the soil – Image powered by

Impressively, worm castings remove these dangerous wastes, leaving the soil safe and suitable for the plants to grow in.

This is especially useful when growing marijuana in reclaimed landfills or other contaminated areas.

2.8 Repel pests

Aside from enriching the quality of the soil, worm castings also protect the plants from pest damage.

Repel Pests
Repel Pests

Studies found that applying them around the plant promotes the release of chemicals that are offensive to insects. In effect, we control pest problems without resorting to chemicals.

3. How do we make it?

While some growers prefer to buy the castings from a local garden supply center, others like to make their own.

The great thing about this method is that we can practice it anywhere.

Whether at home or in the office, anyone can start making worm castings in three easy steps with the help of a few simple things.

Step 1: Select a container

Before getting the worms, prepare a suitably-sized bin for the desired amount of castings.

Select a Container
Select a container – Image powered by

Nowadays, there are so many types of commercial worm containers that are available online.

They are designed for home use, so they are very easy to manage.

Step 2: Obtain earthworms

Now that we have a container, it’s time to get the worms. Most growers prefer to acquire them the easy way and purchase them at the local garden store or online.

Obtain Earthworms
Obtain earthworms – Image powered by

Others like to comb the soil for red wrigglers themselves. But remember that we need at least a thousand of worms if we want to produce a decent amount of castings.

Step 3: Provide the basic needs

Worms need a bedding which we can easily provide by placing shredded newspapers or cardboard for them to tunnel in.

Provide basic needs like shredded newspapers
Provide basic needs like shredded newspapers

Since worms need a bit of moisture, make sure to have extra beddings to absorb it.

Provide the Basic Needs

To create an environment for them to thrive, we also need to add sawdust, cornmeal, straw, or coco coir.

Now for their food, give them kitchen scraps such as fruit and vegetable peelings, coffee grounds, tea bags, grains, and bread.

Growing marijuana worm casting provide their food
Growing marijuana – Worm casting provide their food

Basically, they tend to produce more nutritious castings if they get a well-balanced diet. But avoid giving them meat or dairy which often attracts bad bacteria.

Also, make sure they don’t run out of fresh food to consume. A good rule of thumb is to provide a pound of scraps to a pound of worms.

Step 4: Harvest the castings

Depending on the size of the container and the number of worms, we can harvest the castings every two months.

Harvest the Castings
Harvest the castings – Image powered by

4. How do we use it?

We can use the castings right away or store it for the next growing season. But don’t be disappointed if we extract only a handful from the bin.

In favorable conditions, the worms multiply rapidly and will make more castings if we provide them with enough food.

How do we use it
How do we use it – Image powered by

To use, simply mix the castings with the compost or use it as a side dressing for an indoor plant.

We can also use the “worm tea” by watering it plants that need a boost. Whichever way we use them, we can expect to see satisfying results.

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Final thoughts on using worm castings

There is nothing more natural than using worms to enhance the quality of the soil.

Since they are nature’s fertilizers, they offer the most abundant nutrients with the least harm to the environment.

Hence, growers who practice this method get the most nourishing soil and the healthiest plants.

Learn more about increasing your yields at harvest time with my free mini harvesting guide.

To get started with worm castings, learn everything about it first. While the process comes naturally, we need the knowledge and skills to sustain it.

By doing so, we get decent amounts of the castings that will boost our chances of getting a successful harvest every time.

FAQs about worm castings on marijuana plants

Are worm castings also ideal for seedlings?

Yes, they can be used for seedlings as worm castings will not burn the roots of your plants, unlike synthetic fertilizers. They also have microorganisms that nourish your soil (including potting soil) and help prevent other plant diseases, in addition to providing natural resistance to most pests.

Is using worm castings better than composting?

Because worm castings have a sufficient amount of nutrients and help with plant hydration and aeration, they’re ideal for smaller gardens. However, worm castings can be more expensive than compost and other soil additives.

How often should worm castings be used?

It is recommended to apply a 1/8- to 1/4-inch layer of earthworm castings between each layer of compost materials. Then, every two to three months, you can supplement your bin with fresh castings.

Want to be an expert cannabis grower? You only need practice and learning. Let my blog help you get started.

Have you ever used worm castings on the soil of your marijuana plants? Please share your experience or leave questions in the comments!

Happy growing!


Avatar for Robert Bergman

Robert Bergman


Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations ... See profile

12 comments on “Earthworm castings in growing marijuana”

    • Hi Justin,

      Thanks for your comment. You can use worm casting throughout the entire grow cycle. But keep in mind its relatively higher in nitrogen than potassium and phosphorous, while you want more potassium and phosphorous for your plants during the flowering stage. So you may want to add some additional fertilizer to get the N-P-K ratio a little more in the right range. Make sure to not over-fertilize your plants either, but its nitrogen content is relatively low, so you won’t be very likely to burn your plants with it.
      I hope this helps, but let us know if you have further questions of course!
      Kind regards,

  1. When is a good time to add earthworms to potted cannabis plants? My plant is about to be out of the seedling phase soon and I have a ton of decaying organic matter in the pot. Should I add worms once I see the stem of the plant?

  2. How soon can we add them I put a half a teaspoon of castings to a red solo cup with a two week old plant in them and now I’m worried it might have been too soon I have a bit of yellowing on the tip of a few leaves and a couple look as if the letters are wrinkled

  3. Trying to find out if it’s okay to pot plants in mostly just wormcastting mix or am I just dooming my plants

  4. Casting of earthworms in the plantation of marijuana, is purely organic and extremely rich in both the main nutrients and trace minerals that are essential to the plants.

  5. Hi,

    I actually used ONLY worm casting for the germination/seedling phase. is it a mistake? What can I do to correct it if it’s one.

  6. how about castings from dermestid beetles ? a friend of mine
    is using them to prep skulls and i can the castings , just wondering
    if they would be good or bad to amend my grow soil with ..
    thanks ..garce