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.

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.

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. 

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.

Infographic on the benefits of 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!

When should I apply worm castings?

Because worm castings are very small and you'll be working with a limited quantity, you want to use them as efficiently as possible. These are three of our favorite ways and times to be using them:

  • Indoor Seed Starting: Incorporate anywhere from 10-40% worm castings into your seedling mix when starting your seeds. Conversely, you can purchase our Worm Casting Seedling Mix. This is a pre-mixed seedling mix that you can plant directly into and comes from +3 years of experimenting! 
  • Direct Sowing: Upon sowing seeds into your garden or container, cover them with 1cm of worm castings instead of potting soil or garden soil. Because worm castings have incredible water retention, you will see much higher germination.
  • Transplanting: When transplanting seedlings into your garden, sprinkle 1 handful of worm castings into your transplant hole. Once the plant has been placed in the transplant hole and backfilled with soil, sprinkle an additional 1 handful of worm castings at the base of the plant. Massage in, water, and watch your babies thrive! 

Mind & Soil Happy Customer Testimonial

Customers have been having incredible success with both our Worm Casting Seedling Mix and brand new Seed Starting Kit

Here's what April had to say about the Seed Starting Kit:

I absolutely love the seed starting kit, I had to travel so I thought my plants babies would be late to get started this year but this not the case. The seedlings in the photo are only 3 weeks old, and compared to similar set up I used previously, theses babies are strong and happy, the light and soil and all the fantastic tips from Jordan made a tremendous difference, I am so happy! Also, love the whole Mind and Soils vibe, it's a contagious positive energy. - April L.

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?

    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.

    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! 

    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 Pure Worm Castings or Worm Castings Seedling Mix (that has received countless 5-star reviews). 

    Additionally, you can use the code letsgrow1001 to receive FREE SHIPPING on our Backyard Transplant Kit which comes with both our Pure Worm Castings and 4-4-4 Superfood to give your plants everything they need to thrive! 

    Mind & Soil Transplant Kit

    Our FAVORITE way to use our worm castings is alongside our 4-4-4 Superfood. This combination, the Transplant Kit, provides plants all the nutrients and microbes they need to thrive for the upcoming season! 


    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. Worm Castings 101

    2. HUGE Growth by Potting Up Seedlings with Worm Castings

    3. 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