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. 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: 

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

Okay - So what 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?

worms and worm castings in hand

As worms feast on organic matter it gets coated with beneficial bacteria and enzymes that helps plants absolutely thrive.

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.

Arugula growing with worm castings
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. 

And this is the process that cannot be replicated in any synthetic process. 

We have a very thorough post about what worm castings are and how they help plant growth. Click through the link and read up! It's FASCINATING!

Customer Review of Mind & Soil Worm Castings

Do Worm Castings Really Work?

Countless studies by Universities and agronomists, as well as endless anecdotal experiences by customers have shown worm castings to help plants: 

  • 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.
  • 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 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.

worm castings in hand

You'll be shocked by the beautiful texture and odor-free composition of worm castings! 

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?

applying organic fertilizer while transplanting

We love utilizing our 444 Superfood Organic Fertilizer. But on its own it misses all of the incredible biology and microbial life that worm castings provide. Applied together however, is a match made in heaven! 

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

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.

Customer Review of Mind & Soil Worm Castings

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.

garlic growing with worm castings

One of the best parts about worm castings is that they can be used on 100% of plants. These garlic plants got a handful when planted and another handful as a top dressing in the Spring and are growing incredible well!

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. 

kale planted in 100% worm castings

We have experimented planting in 100% worm castings. While the plant grows and does not display any signs of burning, it also does not grow as well as those that are in 10-40% worm castings. 

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.  Mind & Soil happy customer testimonial

With more than 280 5-Star reviews, customers have been having tons of success with our Worm Castings in their gardens! 

What are the disadvantages of worm castings?

It’s no secret we love worm castings. However, worm castings aren’t right for every gardening situation. So what are the disadvantages of worm castings? Let’s walk through what they are. 

If you’d like a more detailed breakdown of the list below, as well as the solutions we recommend to these combat these disadvantages, then I recommend you check out our 5 Disadvantages of Worm Castings blog post.

Disadvantage #1: Low Quantity

Worms are small, so it stands to reason their castings are small as well. This means that if you’re producing your own worm castings then it will be tough to produce enough for a large garden, if that's they size of garden you have.

Disadvantage #2: Lack of NPK Nutrients

Worm castings’ benefits are not derived from their levels of NPK (Nitrogen, Phosphorus, Potassium). Their benefits are in the bacteria and microbes they contain. In fact, worm castings' NPK count typically come in around 1, 0.5, and 0.5. In other words, quite low!

Disadvantage #3: Long Time to Harvest

Worm farming can be a laborious process that takes months to produce anything of use for your garden. That is not to say you should not attempt your own worm farm! It's simply a reminder that, if using your own worm farm, to plan accordingly if you're wanting to use worm castings!

Disadvantage #4: 100% Organic Matter

Worm castings are absolutely beneficial to growing plants and they also help improve your soil. However, do not make the mistake of planting only in worm castings. Because they’re 100% organic matter it has little structure itself and is best used to better the soil you already have. Planting in only worm castings is not recommended!

Disadvantage #5: Price

Compared to big brand potting mixes, worm castings can seem expensive ($30+ a bag). However, we know their benefits outweigh their costs, and if you’re strategic and efficient, you can absolutely make your worm castings last! 

using worm castings when transplanting

Use your precious worm castings in as targeted of a manner as possible, such as in the base of the transplant hole. A little goes a longways! 

How To Use Worm Castings

Worm castings are beneficial throughout a plant’s entire life cycle, which means they can be used when seed starting, potting up, direct sowing, as well as transplanting. Let’s dig into how to do that exactly!

Seed Starting

We’ve tested this through many experiments, and the results are clear: worm castings improve germination rates as well as help your seedlings grow larger and healthier. There are three key reasons for why worm castings help with seed starting:

  1. They are great at retaining water
  2. They help protect seedlings from disease
  3. They have essential micronutrients that plants need to thrive

Spinach seedling test - worm castings work betterSeed starting test results with Spinach seeds - left seedling has worm castings when starting seeds, right seedling had no worm castings.

How do we use worm castings when starting seeds? By adding it to your Seedling Mix! There are two ways you can go about doing this:

  1. DIY: Add worm castings to an existing mix you already have. Add worm castings until your mixture has somewhere between 10% - 33% worm castings. (Meaning 67% - 90% of your mixture is the original mix.)
  2. Buy a Seed Starting Mix with worm castings already mixed in: Not the DIY type or just don’t feel like mixing it yourself? We’ve got you covered! Our Worm Casting Seedling Mix the perfect mix of worm castings built into it. We’ve seen wonderful results from all the test and comparison we’ve done as well as our customers!
Mind & Soil worm castings seedling mix comparison test results


We go into further detail in our Worm Castings vs. Seed Starting Mix blog post.

Potting Up

When starting from seed, we place our seeds in small seed cells This allows plenty of room for your seed to germinate. Sometimes though, our seedlings grow too big for their seed cell, but it’s still too cold outside to transplant! This is when we pot up, and worm castings can play a role here too.

Here’s how you use worm castings when potting up:

  1. Grab a new pot that is at least double the size of the one your seedling is in
  2. Using the same Seed Starting Mix you used (DIY or from Mind & Soil), fill the new pot ⅓ of the way up
  3. Moisten the seedling mix (we like to do this using 2 full turkey basters of water)
  4. Remove the seedling and gently massage the roots to loosen them up
  5. Place the seedling into the larger pot
  6. Fill in the rest of the pot leaving 1cm from the top of the new pot
  7. Gently compact the soil
  8. Give the seedling mix a healthy drink of water (5 turkey basters of water)

Ta-da! You’ve potted up your place and given it the environment it needs to continue its growth until you transplant it outside.

We go into further detail on the potting up process in our blog post, HUGE Growth by Potting up Seedlings with Worm Castings.

Direct Sowing

Worm castings are just as useful when direct sowing outdoors! Honestly, the process for using worm castings when direct sowing is pretty easy:

  1. Once you’ve placed your seed into its divot simply cover the seed with 1cm of worm castings. 

That’s it. Really.

Direct sowing seeds with worm castings

However, if you want more information on direct sowing in general, we have a much more thorough breakdown of direct sowing in our blog post, How to Direct Sow with Worm Castings. It covers off what direct sowing is, the scenarios in which you’d direct sow vs. start seeds indoors, when to direct sow, and more! Give it a read if you want more information.


When transplanting we want to give our seedlings as comfortable a transition as possible. Using the following steps you’ll ensure they’ll be set up to thrive over the course of the growing season:

  1. Dig a hole for the seedling
  2. Sprinkle in a handful of worm castings (bonus points if you also sprinkle in 1 tablespoon of 4-4-4 Superfood
  3. Remove seedling from its seed cell (or pot if it’s been potted up) and place it into the transplant hole
  4. Backfill the hole with the surrounding soil
  5. Sprinkle 1 handful of worm castings (and another 1 tablespoon of 4-4-4 Superfood) around the stem of the seedling
  6. Gently massage everything into the top 1 inch of soil
  7. Water thoroughly
  8. Smile and be proud of yourself!

If you want to know the full ins and outs of transplanting seedlings, such as the full hardening off process (what it is and why it is important before transplanting) check out our FREE Hardening Off & Transplanting guide.


Worm Castings vs. Compost

I’ll let the cat out of the bag: both worm castings and compost are beneficial to have in your garden. That’s because both provide elements of what a plant needs to thrive, which are:

  • Macronutrients - Macronutrients get their name from plants needing them in large quantities to establish growth and development (nutrients such as, but not limited to, Nitrogen, Phosphorus, and Potassium)
  • Micronutrients - Similarly, micronutrients are nutrients that are needed in smaller amounts (nutrients such as, but not limited to, iron and  manganese)
  • Microbial life - It gets its name from only being visible through a microscope and they are essential to plants by breaking down organic matter in the soil making it easier for plants to access essential nutrients and help to protect plants from disease-causing organisms. 

Compost provides macronutrients and micronutrients, however it does not provide microbes. That’s where worm castings come in. Worm castings are a type of compost (their technical name is vermicompost, ‘vermi’ meaning worm), so it not only provides macro- and micronutrients, but the worm’s digestive system coats the worm castings with beneficial microbes, such as bacteria and enzymes.

We go through worm castings vs. compost in a more detailed blog post: Worm Castings vs Compost - Which is better?

Where Can I Buy Worm Castings?

We have recommendations on where to get your worm castings based on where you live:

Across Canada

Mind & Soil

Obviously we had to mention ourselves :) We work hard to bring you the best soil products, and we are incredibly confident that you’ll love them. We specialize in our soil products as well as gardening kits.  All told, across all our products, we have received over 300+ 5-star reviews!

Here's what we offer: 


Our headquarters are in Squamish, BC, Canada and so we've collected a list of Vancouver-focused stores, given it's our stomping grounds.

  • Jon's Plant Factory
  • Figaro's
  • West Coast Gardens
  • GardenWorks North Shore

We've created a post (Where to Buy Worm Castings in Vancouver) with all the addresses, phone numbers, and website links to each of the companies listed above. Feel free to read through and get in touch with them!

USA + Rest of the World

Unfortunately Mind & Soil does not ship their soil products and gardening kits outside of Canada yet, so your best bet will be to try your local gardening centre. A couple of tips though:

  1. Call ahead to see if your local gardening center sells worm castings
  2. Look for OMRI verified worm castings



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!

Other Worm Casting Articles You Might Enjoy:

  1. HUGE Growth by Potting Up Seedlings with Worm Castings
  2. Worm Castings vs. Seed Starting Mix

    Worm Casting Videos You Might Enjoy:

    1. Before & After - HUGE Growth with Worm Castings
    2. HUGE Growth by Potting up with Worm Castings
    3. Starting Seeds with Worm Castings