5 Disadvantages of Worm Castings

This blog post is a subsection of our Worm Castings 101 - Everything You Need To Know guide. In the 101 guide we cover multiple topics about worm castings, so if you'd like a more thorough walk through of what worm castings are and what they have to offer then click through to read more!


Are there really disadvantages to using worm castings in your garden? While there is plenty of research highlighting how worm castings will improve germination, increase yield, and grow healthier plants, there are also a few downsides that you should be aware of before incorporating them into your gardening routine. In this blog post, we'll take a look at not only the 5 biggest disadvantages of using worm castings in the garden - but also solutions for each of them! Keep reading to learn more!

5 Disadvantages of using Worm Castings

What are Worm Castings?

Worm castings, also known as vermicompost, are the microbial-rich byproducts of composting with worms. These unique fertilizers are an excellent choice for use in a vegetable garden, as they provide the essential bacterial and enzymes needed to grow healthy and robust plants. Furthermore, they feature a number of beneficial soil microbes that help to break down organic matter and make the nutrients more easily accessible to plant roots. 

Whether you're looking to improve your existing vegetable garden or start one from scratch, using worm castings can help ensure that your plants get all the nourishment that they need to thrive. 

Picture of worm castings in hands

Worm Castings, the byproduct of worms, have shown incredible improvements on plant health and yield making them a favourite soil amendment amongst gardeners. 

Why are Worm Castings beneficial? 

Growing healthy vegetable plants can be tricky, especially when you are starting from scratch. In order for veggies to take root and flourish, they need both nutrients and beneficial microbes. 

That's where worm castings come in. 

Worm castings are rich in all the beneficial organic matter that your garden needs, including beneficial bacteria and microbes that help ensure strong plant growth. Whether you're trying to grow a bountiful harvest of tomatoes, radishes, or kale, worm castings will give your veggie plants the boost they need to thrive. 

transplanting with worm castings

Plants such as tomatoes, cucumbers, and basil absolutely thrive when transplanted with worm castings. 

Disadvantage #1: Quantity

Worm castings are often heralded as a miracle product for gardeners. And it's true that they can provide a host of benefits to your vegetable garden, including improved drainage, aeration, and water retention. However, there is one potential downside to using worm castings: their quantity.

Worms reproduce slowly and are only a few inches in size. Because worm castings are made from the excrement of worms, they can be quite hard to come by. Therefore, it can take several months to produce a sufficient amount of castings for a large vegetable garden. As a result, gardeners who rely on worm castings may need to supplement their supply with other organic fertilizers. 

Applying worm castings into the transplant hole

Because of how small the gizzard (mouth) of worms are, it’s difficult to get a significant volume of those incredible worm castings - use them strategically in your garden! 

Solution: Use Worm Castings early on your plants 

A little goes a long way with worm castings, so it's best to add them to your garden early in the season. Our biggest recommendation is to use worm castings early in the season. You can do this by adding worm castings to your seed starting mix at a ratio of 1:3 worm castings to seed starting mix. Additionally, you can sprinkle 1 handful of worm castings into the hole you’re transplanting a seedling into. This ensures all the beneficial bacteria and enzymes are put to use right in the root zone (known as the rhizosphere).

Disadvantage #2: Nutrients

Worms consume organic matter, and as they excrete it, they create worm castings. Therefore, the nutrient profile of the worm casting is dependent on what they ate and most commonly this results in a surprisingly low NPK, such as 1, 0.5, 0.5. 

So why are worm castings so good? The greater benefit of worm castings is the beneficial bacteria, enzymes, and microbes that they’re coated in while passing through the digestive tract. 

But, it’s important to remember that your plants need both the beneficial bacteria and microbes of worm castings, and nutrients. 

Transplanting with worm castings

Transplanting your seedlings with an organic fertilizer alongside worm castings ensures your plants have both the nutrients and microbes to thrive this coming season. 

Solution: Use Worm Castings alongside an Organic Fertilizer

A thriving vegetable garden, for example, will also need additional nitrogen, phosphorus, and potassium. These can be supplied through compost, manure, or an organic fertilizer such as our 4-4-4 Superfood. This is why our Transplant Kits, which come with both Worm Castings and Organic Fertilizer, are so popular! 

Disadvantage #3: Time to Harvest

Harvesting worm castings from a worm farm can be a laborious process, requiring lots of time and manual effort. To break down the key steps:

  • Feeding: First, the worms must eat sufficient organic matter for it to be worthwhile harvesting the worm castings. For a hobby worm farm, this is likely after 3 months worth of feeding them on a biweekly basis.

  • Empty the worm farm: First you start by emptying all the contents of your worm farm onto a tarp or piece of wood.

  • Light Pyramid: Once dumped, you need to build a pyramid pile of the worm castings, beddings and worms. The reason for this is because worms hate light so they will begin to burrow into the middle of the pyramid pile.

  • Scrape: Next, you will begin scraping away the outer walls of this pyramid pile which will now only be worm castings and bedding. 

  • Dry: These materials will be quite moist, so you will want to let them air dry for 24hrs before beginning the sifting process.

  • Sifting: To separate the bedding from the pure worm castings, you will first run all of the material through a 6mm sift and then through a 2mm sift. This will ensure that you end up with 100% worm castings.  

  • Black Gold: It will take a few days of dedicated work and some specific tools but at the end of this, in your hands you will have handfuls of beautiful black gold for your plant babies! 

5 star customer review

To save you all the time of managing a worm farm and harvesting the castings, we ship 100% pure worm castings all across Canada so that you - like Kelly here - can spend all your time in the garden! 

Solution: Purchase pre-sifted worm castings

To save you all of this time, effort, and likely purchasing of resources (i.e. scraping tool, 6mm sift, 2mm, sift, and more) we sell 100% natural and organic Pure Worm Castings and ship all across Canada. With more than 250+ 5-Star reviews, we have countless happy customers that love getting all the worm casting goodness while being saved all the time and manual labour. 

Disadvantage #4: 100% Organic Matter

Worm Castings are 100% organic matter. This means that they don't contain any soil, which can be problematic if you are trying to grow plants in them. In order for plants to thrive, they need a soil that contains not just organic matter but also sand or perlite for drainage and dirt or peat moss for structure. 

So while worm castings are an incredible amendment to your vegetable garden, growing in 100% worm castings would ultimately perform less favourably than a blend that includes multiple inputs. 

Solution: Create or Purchase a Worm Casting Blend

If you wanted to create your own potting mix, you could consider utilize 4 parts compost, 2 parts peat moss or coco coir, 2 parts worm castings, and 1 part perlite. This will create a really beautiful blend that your plants will absolutely love - and maximize the use of your worm castings. 

However, tracking down each of these individual inputs can be a bit challenging, which is why we have put together our Worm Casting Seedling Mix. This is a perfectly blended mix that we have been perfecting for more than 3 years and based on all the 5-Star reviews, it’s safe to say fellow gardeners are loving it

Happy customer testimonial

With our perfectly measured and pre-mixed Worm Casting Seedling Mix, all you need to do is open the bag and get to planting! Shannon is one of the many gardeners who is seeing amazing results with it! 

Disadvantage #5: Expensive

Because the mouths of worms are so small, they can only create a very limited amount of worm castings and it takes both a long time and lot of worms to produce a significant volume of worm castings. As a result, worm castings can end up being fairly expensive. A single bag of Worm Castings can cost as much as $30, making them a difficult fertilizer to justify for small vegetable gardens. 

However, the benefits of Worm Castings may outweigh the cost. In addition to their high nutrient content, Worm Castings also help to aerate the soil and promote healthy drainage. As a result, they can be an invaluable tool for gardeners who are looking to produce large yields of healthy plants. 

happy customer review
While Worm Castings may not be cheap, they’re certainly worth their weight in gold. In Bonnie’s first season of gardening she had all her neighbours asking what her secret to success was! 

Solution: Start a Worm Farm or Use Worm Castings strategically

If the cost of worm castings makes them prohibitive to purchase, you can setup a DIY Worm Farm for less than $20, purchase red wigglers for about $50, and have your own supply of worm castings in perpetuity. The only downside to this is the weekly feeding, care, and then the big harvesting operation.

Conversely, if you do decide to make the investment in building your soil by purchasing worm castings, be sure to use them primarily when starting seeds and transplanting to ensure they are put to use in the most effective area (the root zone).

Tomatoes love to be transplanted with worm castings

While there are some clear disadvantages to worm castings, the benefits far outweigh these disadvantages - as seen by our hundreds of happy customers who purchase new worm castings for each season. By being strategic about when you utilize them, we're 100% confident your plant babies will be thanking you this season!

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

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    • Is it helpful to use worm castings on established plants?


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