Worm Castings 101 - Everything you need to know

You’ve heard about one of the best kept gardening secrets that is quickly being discovered: worm castings. 

Worm Casting Results on Spinach
Two spinach plants with only one difference: The one on the left has received worm castings.


The natural byproduct of worms that has been proven in countless tests (as well as serving as the subject of the Charles Darwin’s last book) to help plants in so many ways: 

  • Grow Bigger - Helps plant grow up to 2x their size.
  • Grow Healthier- The microbes and bacteria coating worm castings help plants grow not only big but also stronger.
  • Taste Better - The abundance of micronutrients provides your vegetables with more flavour than simple NPK fertilizers.
  • Water Retention - Worm castings hold significantly more water than standard mediums - giving your plants the moisture they need to grow.
  • Long Lasting - The worm castings will feed your plants in a slow-release manner giving them a long and consistent supply of nutrients opposed to a quick burst. 
  • Sustainable - Worm Castings divert hundreds of thousands of pounds of waste from landfills and don’t use any chemical processes or harmful fossil fuels.

But given the relative new discovery of worm castings amongst gardeners, questions abound. 

Okay - What are worm castings?

Let’s get started from the very beginning, what exactly are worm castings? The technical term for worm castings is vermicompost. Vermi for the worm, and compost to signify the decomposing process of organic matter.

Organic matter (i.e. yard waste, kitchen scraps) is made up of the macronutrients and micronutrients that plants need to grow. If left to its own devices, over 12-18 months this organic matter would decompose at which point the nutrients become available to your plants.

But, what if it was fed to worms?

Within a worm farm, thousands of worms are fed this same organic matter and quickly consume it. Worms are voracious feeders and can eat half their weight every single day! The food enters their gizzard and then makes it through their digestive track which is where the magic happens. The organic matter is broken down physically but also chemically - with bacteria and enzymes. 

And that’s the magical part.

Worm Casting Results on Arugula Seedling
Two Arugula plants with only one difference: The one on the left has received worm castings


These microbes, bacteria and enzymes have been proven to be incredibly beneficial to plants. As the organic matter makes it to the end of the worm’s digestive tract, it is then excreted in the form of a worm casting - beautifully broken down organic matter coated with all kinds of microbes, enzymes, and bacteria for your plant. 

This is the process that cannot be replicated in any synthetic process. 

And I bet I know what you’re thinking.

But do worm castings smell?

You’ll be shocked by not only the beautiful texture of worm castings but also the fact that they have no scent once so ever. This is a big reason why people love to use it on their indoor plants. 

Given how small worms are, the size of organic matter that passes through their digestive track is no larger than the period at the end of this sentence. This creates a beauty sand-like end product. 

I know we needed to get that out of the way.

Why are worm castings so beneficial?

To understand why worm castings work so well, we need to first understand: what does a plant need to grow?

That covers the chemical side, but what about the biological side?

Think of the last bag of soil you bought. What’s the one nutritional piece of information that comes to mind?


When we think of standard soil mixes we buy from a garden center, it usually only has 1/6 of the areas above: Primary Macronutrients. This is why you’ll see the NPK rating displayed in big bold letters.

But, NPK is only one part of what plants need - and these mixes miss out on the rest.

Worm castings are a much more dynamic product and include macronutrients, trace micronutrients and microbes.

Why worm castings work so well

Think: Processed Foods vs. Organic Diet

To explain it in terms we’re more familiar with, what would you prefer to feed a fast growing child: processed foods sitting on a shelf or fresh organics packed with nutrition? 

Processed foods have been around for a long time, have the key nutrients that we need, and are available at a very cheap price. But if a diet consisted only of these processed foods, the child would likely experience an immediate boost in sugar before quickly crashing and ending up feeling lethargic. 

On the other hand, an organic diet supplies us with not only all the nutrients we need but also the minerals and vitamins in an unaltered form and much better gut health.

When should I apply worm castings?

You can use worm castings all throughout the season, but the absolute best time to use them is at the beginning of a plant’s life cycle in its seedling mix.

Worm Casting Customer Reviews Five Star

Using worm castings, peat moss, compost, and perlite as a seedling mix gives your plants all of the macronutrients, micronutrients, microbes, and bacteria it needs while it establishes its root structure. You get an incredible ‘bang for your buck’ using it at this stage because the entire root system is limited to a pot or seedling cell that is only a few inches wide. 

When your seedlings are ready to be transplanted into their forever home (garden beds, containers, or grow bags etc.), you can apply another 1-2 handfuls at the bottom of the hole they’ll be planted in and another 1-2 handfuls at the base of the plant once it has been backfilled. 

Lastly, worm teas are a great way to add additional nutrients and microbes to your soil throughout the season - we’ll touch on this in its own post!

Can worm castings burn my plants?


The concept of “burning” plants came into existence with the emergence of synthetic chemical fertilizers. Humans use tons of fossil fuels to create fertilizers that are incredibly potent and therefore could burn your plants. 

Worm castings, on the other hand, are a natural process.

The worm castings that you apply to your plant are simply organic matter that have been digested and coated with microbes and bacteria that your plant love. 

We’ve even tested growing plants in 100% worm castings and there was zero burning. However, this does not mean you should plant in 100% worm castings. There is not enough soil structure or drainage for the root systems to sprawl efficiently - and therefore growth will be stunted. 

If I can’t over-apply, how much should I use?

The common practice with worm castings is anywhere between 20% to 50% of the overall soil quantity. A few specific use cases:

  • Seeds: For starting seeds you can use up to 50% of the mixture as worm castings. The remaining 50% should be primarily a growing medium (i.e. compost, peat moss, coco coir) and a drainage medium (i.e. perlite, vermiculite). They can grow in this exact mixture until you are ready to transplant them into their forever home.
  • Seedlings: If you are purchasing seedlings from a store, you want to incorporate worm castings immediately. Either re-plant them into a mixture similar to the seeds above or leave them in their pot and add 1” of pure worm castings to the top of this pot. As you water them, the nutrients and microbes will move down and into the root system.
  • Garden Bed: When your seedlings are ready to move into a garden bed, container, or grow bag, you will start by digging a hole. Place 1-2 handfuls of worm castings at the bottom of this hole and backfill with the existing soil. Once backfilled, place 1-2 handfuls of soil at the base of the plant and spread it out evenly. As you water the seedling, the nutrients and microbes will work their way into the soil and the root system will grow into the worm castings towards the bottom.
  • Indoor plants: You can work 20-30% worm castings into your existing potting mixes as you prepare to transplant your plants. It’s important to note that worm castings retain significantly more water than standard growing mediums (i.e. peat moss, coco coir). Therefore, keep a close eye on moisture levels of your plants once they have been transplanted as you adjust to growing with worm castings. Alternatively, if you are not needing to transplant your plant you can simply apply 0.5” - 1” of worm castings across the top of its existing soil.

What plants benefit most from worm castings?

We’ve been playing around with worm castings on all kinds of plants and they all have loved worm castings, including:

Outdoor plants display more growth than indoor plants - but this is primarily due to the outdoor plants being annuals and growing at incredible rates for their season before going to seed. 

What are the disadvantages of worm castings?

Depending on what plants you’re growing and the inputs of your worm castings, it is possible that your plants may still need additional macronutrients and micronutrients. 

For instance, tomatoes and squash are very hungry plants that produce fruit through flowering. As such, our recommendation is to use either a compost or a balanced organic feed to top up your plants with the nutrients they need. If you have been adding compost to your garden beds or applying an organic feed with consistency then you will likely have more than enough nutrition throughout your beds.

Where can I buy worm castings?

We have been hard at work the last year testing worm castings and are incredibly confident that you’ll love our Worm Castings Seedling Mix (that has received countless 5-star reviews). From all our tests over the last 2 years it is our highest performing blend and will give your plants everything they need to grow big, healthy and yield delicious vegetables.

Buy Worm Castings now in Canada



How do I store my worm castings?

You can store your worm castings in a cool & dry place - such as your garage. To keep the microbial life alive you will want to keep them slightly moist and oxygenated. As such, we’d recommend taking them out of the Mind & Soil packaging and into a 5-gallon bucket with small holes drilled in it and some wet newspaper on top. Other than that they don’t need any special care or maintenance - just to be kept cool and dry until being put to use.

Do they go bad at a certain point?

When stored properly, multiple studies have shown that they do not lose any of their nutritional or biological value for more than three years

How to make compost tea and worm tea?

To supercharge your garden, consider brewing a Worm Tea (which we cover in Step 3 of our end of season maintenance method). In a 5-gallon pail you will add non-chlorinated water, 2 cups of worm castings, 2 cups of compost, and 2 tablespoons of molasses. Once these have been added to the pail, you will add an oxygenator to ensure the tea remains aerobic and the microbes can reproduce. Brew in this manner for 36-48hrs and then apply immediately to your soil and foliage. This will give your beds or containers a beautiful boost of nutrients, microbes, and beneficial bacteria. 

Where to buy worm castings in Canada?

We ship our Worm Casting Seedling Mix all across Canada!