By Amy Stross

Worm castings — or worm manure — are the richest known natural fertilizer. They contain an impressive list of minerals and nutrients in quantities that outperform other organic materials and manures. The phosphate, nitrogen, and potash levels in worm castings are through the roof, and all of these are essential to plant growth. 

Livestock manures are important soil amendments because of the volume of manure the animals produce compared to the small bodies of worms. However, livestock manures can burn plants if added in excess, or if added before the composting process is complete. They are also not immediately bioavailable to plants. 

With worm castings, however, neither of these concerns is a risk. The nutrients in worm castings are immediately available to plants, and there is no upper limit to the quantity of worm castings you can safely apply—though even a tablespoon of castings per plant would be enough to improve plant health and vigor. That’s because worm castings contain 50% more humus than regular garden soil, which is the organic component of soil necessary for plant growth and for increasing beneficial soil microorganisms. Worm castings help plants grow vigorously and help protect them from disease by forming beneficial relationships with the roots of plants. They also help retain moisture in the soil. Worm castings can be easily purchased in bags from your local garden supply store, but it’s just as easy to construct your own worm bin and make your own. 

If you use composted livestock manure as a soil amendment, mixing it with worm castings can skyrocket its nutrient content and its bioavailability. We don’t keep livestock at Tenth Acre Farm, but we have a regular composting system that yields finished compost as a soil conditioner. We also occasionally get horse manure from a local horse stable. We mix both of these soil conditioners with our very own worm castings to make the ultimate fertilizer. 

Vermicomposting is a fancy word for worm composting. It is popularly promoted as a way for space-challenged city dwellers to dispose of kitchen scraps because of the small footprint of a worm bin. However, I think worm composting is a boon for all gardeners because worm bins are so inexpensive, easy to make, and yield such an important soil amendment— for free! 

TIP: Worm bins are an easy way to continue composting throughout the winter when the regular compost bin freezes up. I keep my worm bin in the garage, and when the compost pile outside is frozen in winter, we can continue to compost our food scraps by adding them to the worm bin. 

Worm Bin Care 

Feed the worms about one cup of food scraps each week for the first few months. (Remember to avoid feeding them citrus fruits, hot peppers, garlic, or onions.) As the worms look bigger and more numerous, you can increase the amount of food scraps you give them each week. 

How to Construct a Worm Bin 

Materials 

• 2 (20-gallon) plastic totes + lids—dark-colored, no clear plastic 

• Drill with 1/4” and 1/16” drill bits 

• Shredded office paper and newspaper— enough to fill half of one bin (no glossy paper)

• Spray bottle with water 

• Red Wiggler worms (1,000) 

• Few handfuls of garden soil or leaves (optional) 

• 1 cup of food scraps (fruits, veggies, eggshells, coffee grounds. NO citrus fruit, garlic, or hot peppers) 

• 4 bricks 

Instructions

 1. Drill about 35 holes in the bottom of each plastic tote using a 1/4” drill bit. This is for drainage and for the worms to migrate upward from a full bin to a new, empty bin. 

2. Use the 1/16” drill bit to drill about 60 ventilation holes just under the top edge. Also drill about 35 ventilation holes in ONE of the lids. 

3. Add half of the shredded office and newspaper, moistening it with the spray bottle. It should feel like a wrung-out sponge. This is the bedding. 

4. Add the worms, and then add a few handfuls of loose garden soil or leaves if desired—not required. 

5. Add food scraps and spread it all out evenly. 

6. Top with the other half of the shredded paper and moisten well. 

7. Locate your bin’s ideal permanent place. The worms don’t like temperature extremes, such as really hot summers and really cold winters. Generally, 55 to 75 degrees Fahrenheit (F) is ideal. We keep ours in the attached garage. Dark and or shady environments are also preferred. 

8. Place the lid without the holes on the ground and place a brick in each corner. 

9. Set the full bin on top of the bricks and close it with the lid (the one with holes). 

10. To feed the worms, pull away the shredded paper on top, pour in the cup of food, and then replace the shredded paper so all food is covered. 

If fruit flies or mites develop, it is a sign that you may be giving them more food than they can handle. Simply stop feeding them for a few weeks until the pests go away and the conditions balance out. 

Over time, the bedding (shredded paper) will break down. Just add more shredded paper if that happens, moistening it with the spray bottle. Monitor the moisture level. The contents should always feel like a wrung-out sponge. If lots of liquid seems to be draining out the bottom, it could mean that you’ve added too much water. Just let the moisture levels balance out on their own, perhaps lifting the lid once a day to allow excess moisture to escape. 

How the Worm Bin Works

Vermicomposting occurs in one main bin. When the bin gets full, stop feeding the worms for about one month. They will continue to process the existing food scraps. By the end of the month, they will be hungry and willing to travel to find a food source. Take the lid off, and place the second empty bin directly on top of the compost surface of the (bottom) full bin. 

Add bedding and food (always keep food covered) to the new bin on top, and wait two months for the worms to migrate up through the holes to the new bin. Only add more food if it appears that a good portion of the worms have migrated up. The bottom bin should be mostly worm castings at this point, and easily harvestable for the garden. If you notice a few worms or uncomposted scraps still hanging around in the finished compost, they should be easy to remove and add to the new bin to continue composting. Use the worm compost to improve garden soil or to start seedlings in pots.

Living on a small lot limits my ability to compost in an ideal way, but if I “had my druthers,” I would have a compost heap for sticks and brush. The 3-bin compost unit would make amazing compost out of food scraps, leaves, grass clippings, and weeds. And my worm bins (two of them) would produce fertilizer-rich worm castings that, when mixed with finished compost, would make building garden soil a breeze for very little cost and external inputs. All in all, the combination of composting methods you use will be dependent on how much space you have and other unique factors. 

Through no-till farming, an informed use of soil amendments, and active composting systems, you’ll be well on your way to creating a healthy soil ecology that will form the basis of a thriving food production system!

This blog post is a sneak peek inside The Suburban Micro-Farm by Amy Stross, owner of www.TenthAcreFarm.com. Reprinted with permission from the author via Twisted Creek Press and Chelsea Green Publishing Company.

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