Best Worm Castings for Cannabis

These nutrient-rich droppings from earthworms are a game-changer in the world of organic gardening.

Worm castings, also known as vermicast, are the end product of the decomposition process of organic matter by earthworms. Essentially, it’s worm poop packed with nutrients and beneficial microorganisms that plants love. Unlike synthetic fertilizers, worm castings provide a slow-release of nutrients that won’t burn your plants.

Worm castings are produced through a process called vermicomposting. Earthworms consume organic waste like kitchen scraps and garden clippings, breaking it down into a dark, crumbly substance rich in essential nutrients. This organic matter passes through the worm’s digestive system, where it’s further broken down by beneficial bacteria and enzymes.

Worm castings are loaded with essential nutrients such as nitrogen, phosphorus, and potassium, which are vital for plant growth. They also contain trace elements like calcium, magnesium, and iron. Worm castings host a plethora of beneficial microorganisms that improve soil health and plant immunity.

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Written By Roy Stevens

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Quick Answer

“Worm castings act as a soil conditioner, improving its texture and aeration. This is crucial for cannabis plants, as it allows roots to penetrate deeper and access more nutrients and water. A well-structured soil also reduces the risk of root diseases. One of the standout features of worm castings is their ability to retain moisture. The humus in castings can hold several times its weight in water, ensuring that your cannabis plants stay hydrated longer. This is particularly beneficial in arid climates or during dry spells. Teeming with beneficial bacteria and fungi that help break down organic matter and make nutrients more accessible to plants. These microorganisms also fend off harmful pathogens, creating a healthier growing environment for your cannabis.”

For US growers some popular brands include Mountain Valley, Wiggle Worm, Brut, Urban Worm, and Dr Verm. UK growers can pickup brands such as Wormganix, Baltic, and Elixir Gardens. Occasionally Wiggle Worm may also be available depending on stock.

Tried & Tested

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Urban Worm Castings


Wiggle Worm


Brut Worm Castings

Benefits of Using Worm Castings

Enhanced Plant Growth

Worm castings provide a balanced nutrient profile that promotes vigorous growth and robust flowering in cannabis plants. The slow-release nature of these nutrients ensures a steady supply, preventing nutrient burn and deficiencies.

Improved Soil Health

Adding worm castings to your soil not only enriches it with nutrients but also improves its overall health. The castings enhance soil structure, increase microbial activity, and improve water retention, creating an optimal growing environment for your cannabis plants.

Pest &Disease Resistance

The beneficial microorganisms in worm castings help protect your plants from pests and diseases. They create a hostile environment for harmful pathogens and boost your plants’ natural defenses, reducing the need for chemical pesticides.

Types of Worms

Red Wigglers

Red wigglers (Eisenia fetida) are the most popular worms used in vermicomposting. They thrive in decomposing organic matter and produce rich, nutrient-dense castings. Red wigglers are efficient converters of kitchen scraps and garden waste, making them ideal for home composting systems.

European Nightcrawlers

European nightcrawlers (Eisenia hortensis) are larger than red wigglers and are known for their deep burrowing behavior. Their castings are equally rich in nutrients, and they can tolerate a wider range of temperatures, making them suitable for outdoor composting.

African Nightcrawlers

African nightcrawlers (Eudrilus eugeniae) are another excellent choice for vermicomposting. They are known for their rapid reproduction rate and ability to consume large quantities of organic matter. Their castings are rich in nutrients and beneficial microorganisms, providing an excellent boost to your soil.

How to Use Worm Castings

Soil Preparation

Start by mixing worm castings into your potting soil or garden bed. A good rule of thumb is to use 10-20% worm castings by volume. This will provide a nutrient-rich base for your cannabis plants and improve soil structure and water retention.

Top Dressing

Top dressing involves applying a layer of worm castings on the surface of the soil around your plants. This method allows the nutrients to slowly leach into the soil with each watering, providing a steady supply of nutrients to your cannabis plants.

Compost Tea

Compost tea is a liquid extract made from worm castings that can be used as a foliar spray or soil drench. To make compost tea, steep worm castings in water for 24-48 hours, then strain and apply the liquid to your plants. This method delivers nutrients and beneficial microorganisms directly to the plant roots and foliage.

Common Mistakes

While using worm castings is relatively straightforward, there are a few common mistakes to avoid to ensure the best results for your cannabis grow.


While worm castings are beneficial, too much of a good thing can be harmful. Excessive amounts can lead to nutrient imbalances and waterlogging. Stick to the recommended application rates to avoid overfeeding your plants.

Inconsistent Use

Consistency is key when using worm castings. Applying them sporadically won’t provide the same benefits as a regular feeding schedule. Incorporate worm castings into your routine to ensure your plants receive a steady supply of nutrients.

Poor Quality Castings

Not all worm castings are created equal. Low-quality castings may contain contaminants or lack the necessary nutrient profile. Source your worm castings from reputable suppliers to ensure you’re getting a high-quality product.

DIY Worm Castings at Home

If you’re up for a little adventure, you can produce your own worm castings at home. It’s a rewarding process that allows you to recycle kitchen scraps and garden waste while producing a valuable soil amendment.

Setting Up a Worm Bin

Start by setting up a worm bin in a cool, shaded area. Use a container with adequate ventilation and drainage, and fill it with bedding material like shredded newspaper or coconut coir. Add a handful of red wigglers or European nightcrawlers and start feeding them small amounts of kitchen scraps.

Feeding Your Worms

Worms thrive on a diet of fruit and vegetable scraps, coffee grounds, and eggshells. Avoid feeding them meat, dairy, and oily foods, as these can attract pests and create unpleasant odors. Feed your worms regularly and monitor the moisture levels in the bin to keep them happy and productive.

Harvesting Castings

After a few months, your worms will have transformed your kitchen scraps into rich, dark castings. To harvest the castings, move the bedding to one side of the bin and add fresh bedding to the other side. The worms will migrate to the fresh bedding, allowing you to collect the castings from the original side.

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