Vermicompost: A Practical Guide On Worm-POwered Compost

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How to Use Worm-Powered Composting for Improved Soil Health, Stronger Seedlings & Higher Yields on the Farm

Simplifying the Journey to Soil Health

We all want healthy living soil to make our job easier as farmers. Living soil makes it easier to grow plants that are more resilient to pest and disease pressure and produce high yields of beautiful food that sells.

But managing soil health can feel like a complicated journey: organic matter, balancing pH levels and 27+ macronutrients and micronutrients, fungal to bacterial ratios, etc. There’s a lot to learn! And there is never a “silver bullet” for solving complex systems like soil health. 

But there is low-hanging fruit that we as regenerative farmers — farmers that focus on improving and ‘regenerating’ the natural systems our production is based on — should not leave out of our soil management toolkit. Vermicomposting is at the top of my list. 



Introduction to Vermicompost

Vermicompost — worm-powered composting — is a time- and cost-efficient method of creating healthy living soil on your farm in the long term. It can also be used to produce immediate benefits for the quality of your seedlings, microgreens, and field crops. Vermicomposting aims to quickly and affordably turn food and field scraps into living compost, full of microorganisms and valuable nutrients that are immediately available for plants to uptake and thrive on.

We use vermicompost on our two-acre intensive vegetable farm. I think you will see undeniable results on almost any farm or garden. The end product of vermicompost is richer in nitrogen, phosphorus, calcium, and magnesium. Once you take the time to start up a new system, it almost runs itself.

Setting up your system can take just a couple of hours of sourcing materials and one-time startup work, then as little as 10 minutes of weekly maintenance. You’ll be able to produce hundreds of dollars worth of worm castings each year, with much higher quality than expensive store-bought bags.

Disclaimer: Vermicompost does not remove the need to maintain sufficient organic matter levels in your soil or balance other nutrient deficiencies. These are still basic things you need to do for your crops to grow optimally. 

That said, vermicompost is a relatively simple practice that will help you along the road to balancing your basic soil needs. Once your baseline is set, vermicompost as a continued practice can be an easy perennial method that keeps your soil surviving and thriving every growing season.

Practical Uses of Vermicompost

On our farm, we mix vermicompost directly in potting soil for thousands of seedlings every month and approximately 40-50 trays of microgreens per week. We mix vermicompost in water for soaking cover crop seeds, and we brew compost teas and extracts for spraying in the field. We even spray it on regular compost piles (non-worm-powered) to speed up and improve the quality of the compost they produce!

Again and again, the results are clear. We have seedlings that never get nutrient-stressed in the trays and noticeably higher yields in the field or our microgreens trays. 

In my experiments, when vermicompost is added as just 5-10% of the potting soil mix, I have seen as much as 20% higher yields of pea shoots and radish microgreens, and 30% higher yields of sunflower shoots, compared to a tray without any vermicompost mixed in the potting soil. I believe this is time very well spent for the results we get in return.

Food Safety Considerations 

One topic worth discussing is food safety. In general, vermicompost fresh from a bin on our farm is treated the same way as animal manure, which should be aged to kill potentially harmful pathogens before applying it to the food. 

We age vermicompost for at least 30-60 days before applying it directly to plants. We always have two or three surplus bins full of vermicompost that have been collected from our worm bins weeks or months ago, and we keep track of which ones are the oldest and newest to avoid accidentally applying fresh vermicompost. These bins still have access to oxygen, and we add a bit of water regularly so the microorganisms stay alive and healthy for future use. Perhaps this seems to be an overabundance of caution because vermicompost is likely much less of a risk factor than fresh cow or pig manure. However, we like to use the precautionary principle whenever uncertainty enters the picture. Better safe than sorry.

Here are a few general rules we go by for food safety:

  • We never apply vermicompost in any form in the same 30-day period that it will be harvested for both sanitary and practical reasons.
    • Sanitary, because would you want to tell your customers that the lettuce they are about to eat, even if it has been double washed (which ours always is), has had fresh worm poop sprayed on it in the past month? 
    • Practical because there would likely be little to no visible benefit in applying side dressing to most fully mature plants less than 30 days before harvesting.
    • Best to do this well ahead of time at 30-60 days out from harvest to see real benefits.
  • We never spray compost extracts directly on leafy vegetables in the field like lettuce, arugula, Swiss chard, kale, or the like. 
  • I recommend using a 30-60 day rule for applying vermicompost: 
    • 30 days before harvest for when the vermicompost is being directly applied or sprayed on the non-edible parts of the plant
    • 60 days aged vermicompost when being applied to edible parts of the plant
  • For microgreens, which are harvested 7-10 days after seeding, we always use our most aged compost, which was collected over 60 days ago.
    • Vermicompost is approximately 5-10% of the mix with potting soil.
  • For seedlings, the product of which will be harvested 60-90 days in the future, we have used fresh in the past because it will be aged 60-90 days by the time harvest takes place.
    • However, we still tend to use our aged compost because we have so much available and haven’t seen any reduction in the quality of products when using aged vermicompost.
    • Vermicompost is approximately 5-10% of the mix with potting soil.
  • For direct soil applications, such as side-dressing tomatoes and peppers, we mix in 10-20% fresh vermicompost, with the rest being compost from our passive compost pile along with any other amendments.
  • For foliar sprays, we use aged vermicompost that was removed from the system over 30 days ago.
    • One cup of vermicompost per gallon is plenty, then we triple strain the liquid with paint strainer bags in 5-gallon buckets (available at paint and hardware stores). This ensures no solid matter will clog up our backpack sprayer.

How Vermicomposting Works — The Simple Overview 

We’ll go into greater detail below about setting up your vermicomposting bin. Here is a quick overview so you can get a mental picture of how the system works:

  1. Find a warm and dry space (ideally 60-80F) that you can use to operate the system year-round, preferably indoors, to protect your system from direct sun and rain. 
  • We put our system in our toolshed in the summer and our heated workshop (where we grow microgreens) in the winter.
  1. Food scraps are placed into a container with drainage holes at the bottom.
  2. Worms are added to their new home. We use “red wigglers” for reasons mentioned later.
  3. Worms digest food scraps, while any excess moisture exits via the drainage holes.
  4. Trillions of microorganisms in the intestinal tracts of the worms are released through excretions (worm poop), creating nutrient-rich vermicompost.
  5. Food scraps are regularly added to the topmost layer of the system; new bins are added on top as needed.
  6. Worms will migrate upward through the drainage holes of higher bins to access new food sources, leaving behind finished vermicompost in the lower layers.
  7. Vermicompost is collected for various applications around the farm, transporting the beneficial microorganisms directly to your soil.
  8. Now you have a self-sustaining, worm-powered microorganism factory!

Expanding Your Vermicomposting System

Worms are self-repopulating, so your population will increase surprisingly quickly if managed correctly. Of course, the population will only increase according to the amount of food you give them (without overfeeding them, which can kill them later). 

After running our system, I now add anywhere from 5-10 lbs of food scraps per week, which according to the 2:1 ratio, indicates there are now approximately 3-5 lbs of worms in our system at any given point, a 200-400% increase over my original purchase. 

If I had chosen to, I could’ve bought or made a second system and moved some of the worms to the new system to continue increasing the population, but one system is enough to meet our needs for our uses. 

Scaling Up A Vermicompost System — Pros and Cons

In my view, a small container system is a perfect size for our market farm. We’re not producing massive amounts of quantity for broadcasting in the field or dumping wheelbarrows full as we do with animal manure-based compost. 

One fact about vermicomposting is that, especially in the beginning, it will be a smaller-scale system than a passive compost pile. Your input is limited by the number of worms you are willing to buy (always remember the rule of ½ lb. of food per day per 1 lb. of worms). Overfeeding = thermophilic = death.

Instead, we’re creating the highest quality possible compost to use strategically in specific use cases where it has the greatest per area contact with our seeds and roots, generating the most benefits and highest impact: mixing with potting soil for seedlings, microgreens, and potting up tomatoes and peppers, or brewing compost teas and extracts for soaking seeds and applying foliar sprays.

The limiting factor in a worm-powered compost system is… the worms. Specifically, how much food and raw organic matter they can consume and ultimately break down into rich finished compost. This is why we choose to do both vermicompost and passive composting on our farm. The sheer volume of food and field scraps our farm produces at some times of the year is simply too much for the number of worms we have to digest, and we don’t have the year-round indoor space available to keep a large vermicompost system active. Instead, we simply put most of our field scraps in our passive compost pile and feed the worms what they need. We then use compost teas from our vermicompost to add more healthy biology to our passive pile.

In general, we use vermicompost for quality and passive composting for quantity

However, if you have space for a larger system and the desire, the formula is pretty simple: more worms + more food to break down = more vermicompost.

Let’s discuss a couple of methods for expanding your system. This is not an exhaustive list, but it will give you a glimpse of the trade-offs of managing a larger vermicompost system.

Method 1 (Not Ideal) — Simply Adding Worms to a Large Passive Compost Pile

In the past, I’ve considered having a makeshift large-scale vermicompost pile by simply adding worms to a passive compost pile after the thermophilic phase has passed, i.e., temperatures have dropped well below 90F and pose no risk to the worms. However, there are a few reasons I wouldn’t advise this because it can tend toward messy results: 

1) Inconsistency of compost quality since you have no control over where the worms travel.

2) Difficulty harvesting finished compost because without controlled feeding (intentional upward or sideways migratory feeding), the worms again can travel and reproduce anywhere randomly throughout the pile, so in attempting to collect the compost, you’ll likely be removing many of your red wigglers, specifically chosen composting worms, and moving them to your field, where they will not thrive and may simply die, which is a waste.

3) An uncontained pile that is sitting on the ground will allow worms to leave your compost pile, which they will do if the environmental conditions (temperature, moisture, food, acidity) become less than ideal

4) In the winter, all of your worms will die in the freezing temperatures or migrate into your subsoil below your pile until they reach comfortable levels, with no guarantee that many will return to your pile in the spring (a contained outdoor system isn’t a fix for this because it will simply guarantee they’ll freeze in the pile).

Method 2 — A Sideways (or Horizontal) Migratory System. 

This type of vermicompost system is discussed in some detail by Troy Hinke in his compost tea podcast, ‘What’s Brewing’.

Imagine the same mechanics of an upward migratory vermicompost system (the premade or DIY systems shown above) but flipped on its side, so rather than the worms traveling up to new food sources, they simply travel horizontally as you add fresh food. Rather than requiring vertical layers divided by drilled holes, you simply have a completely open system that the worms can travel freely through, but you can control the direction of migration by starting from one end and feeding to the other end (left to right, or right to left)

This is a system that could be made with simple materials, such as plywood reinforced by 2×4 boards (use untreated wood so as not to damage the worms with chemicals). I’ve considered making a sitting bench-height system with a wood panel cover I could remove when it’s time to feed. Stainless steel would also work, and would never have to be replaced with wood. 

The size of the system would be up to you as the builder, but I would keep in mind ease of use and being able to collect the finished vermicompost as the main consideration in your dimensions. In our workshop, I would build perhaps it 3-4 feet in height and depth, and approximately 8-12 feet in length (the length would be determined by your available space in your shed, garage, or workshop if you like).

Here are examples of a smaller version of this that could be expanded to much longer systems (photo credit left: rootsimple.com; right: redwormcomposting.com):

Note the lack of drainage holes in the left image. It is recommended to drill small holes every few inches to allow excess moisture to leave the system in case of overfeeding or rain intrusion.

If you, like us, are limited by your indoor space, a horizontal system like this could theoretically be built outdoors to use throughout the spring and summer. Then in the fall, before deep frosts arrive, you could collect as many worms as you can from the freshly fed side of this horizontal system and move them into a smaller indoor system like the ones described above, to keep them safe for the winter. Then you’ll have a healthy population of worms ready to repopulate your outdoor system in the spring and start over again!

A system like this could produce hundreds of lbs. of nutrient-rich worm castings each year, valued at thousands of dollars. If it’s too much for you to use yourself on your farm, it could even become a source of revenue for your farm. 

Keep in mind that every new venture on a farm is a trade-off of time vs. value. We’ve opted to keep our system small and manageable to focus on growing high-quality vegetables, greens, and microgreens, which keeps us plenty busy without throwing in a vermicomposting business on top of it. A small system could take 10 minutes per week to manage, and a large system may not take that much longer to manage. However, marketing and delivering compost to clients when you have a whole list of things to do on the farm to maintain crops is quite another matter. A good bet is to start small, see how you like your results, then go from there.

Conclusion

There you have it! This has been a beginner’s crash course in vermicomposting. You now know why vermicompost is valuable, how it can be used, how to start your system from scratch, and the pros and cons of expanding. Take a look at the websites of Smart As Poop (Canada) or Meme’s Worms (US) to learn more and order your first batch of worms. Happy composting!


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About the author

Seth Davis

1 comment

  • Seth this is a helpful article. We have for a long time been purchasing 2-3 cubic yards of vermicompost for use in potting mix. I’ve not ventured in to production but have considered it. I’d like a bit more detail on your system. What kind of containers/size or container are you using? how many bins do you have going and what kind of bedding do you use?

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