We all know that we should fertilize our gardens regularly, but many of us are unsure of how to do it properly and safely without the use of chemical fertilizers. After all, those chemical fertilizers have a label with specific directions, while organic material does not. In this article, find out how to make your own natural fertilizer at home—in the right quantity—with very little effort.
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Worm Castings—The Fertilizer You Need
Worm castings are basically worm poop. Like any animal manure, it is the end product from the digested organic matter that the worms ate.
Did you know worm castings are the richest natural fertilizer that we know of? They contain an impressive list of minerals and nutrients in quantities that outperform other organic materials and manures. Phosphate, nitrogen, and potash quantities are through the roof, and are all essential to plant growth.
Livestock manures are important soil amendments because of the volume of manure the animals produce. However, they can burn plants if added in excess, or if they’re added before the composting process is complete. Their nutrients are also not immediately bioavailable to plants.
With worm castings, however, neither of these are a concern. The nutrients in worm castings are immediately available to plants, and there is no maximum limit to the quantity of worm castings you can apply (meaning you can’t accidentally apply too much).
Any amount is safe, 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 that is necessary for plant growth and for 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, but it’s just as easy to make your own worm castings.
If you use composted animal manure as a soil amendment, mixing it with worm castings can skyrocket its nutrient content and its bioavailability.
We don’t keep livestock here at Tenth Acre Farm (yet), but we have a regular composting operation that yields finished compost as a soil conditioner. We also occasionally get horse manure from a local horse stable. We plan to mix both of these regular amendments with our very own worm castings.
Cultivate your Own Worm Castings with Vermicomposting!
Vermicomposting is a fancy word for worm composting.
It is popularly discussed as a way for city dwellers to dispose of kitchen scraps because of the small footprint of a worm bin. However, worm composting is a boon for all gardeners because worm bins are so easy to make and yield such an important soil amendment.
We keep our worm bin in our garage, and when the compost pile outside is frozen in winter, we can continue to compost our food scraps by feeding the worm bin.
There are many store-bought varieties of worm bins, but DIY worm bins are so easy and inexpensive to make.
Our First Worm Bin
My brother gave us our first worm bin made out of a plastic tote (with worms) one Christmas. He just drilled two holes in each side for ventilation. We had been wanting one, but were afraid we would do it wrong and attract bad smells or fruit flies. Now we had no choice, the worms were in the mail, on their way!
We did have the Worm Bin Saga of 2014. In our first few months, our worm bin had really bad smells, produced fruit flies, and got infected with mites. See how we got rid of fruit flies.
However, we learned that we had simply been doing it wrong. When we first added the worms to the bin, they were really tiny baby worms. And we gave them enough food to feed an army! The food just rotted. It was bad.
Having a worm bin isn’t really that hard. Just be sure to only feed them about a cup’s worth of food scraps each week for the first few months. After that, they should be able to handle all of your household’s food scraps.
But I digress.
Harvesting Worm Castings
After keeping worms for a year, we felt more confident in how much to feed the worms. But the problem was harvesting the castings.
Single Bin Harvesting a No-Go
With our single bin, we tried feeding them only on one side, hoping that when that side filled up we could begin feeding them on the other side. In this plan, eventually the worms are supposed to migrate to the new side where the food is, allowing us to harvest the castings on the first side.
We discovered that this didn’t work in our little bin. There were always plenty of worms in all areas of the bin.
An alternative solution for small bins is to spread out a sheet of plastic on the ground and scoop out double handfuls of worm castings, placing each in a pile on the plastic in a cone-shape, like a party hat. After a few hours, the worms are supposed to migrate to the bottom of their cone, allowing you to harvest the top 2/3 of each pile.
But this just sounded like a lot of work, and many people told us it didn’t work all that well.
So we decided to build a new bin with easy harvesting in mind. After some internet research, we decided on the following plan.
Worm Bin, 2.0
- 2 (20-gallon) plastic totes + lids (dark colored, no clear plastic)
- Drill + 1/4″ and 1/8″ drill bits
- Shredded office paper and newspaper – enough to fill half of one bin
- spray bottle with water
- Red Wiggler Worms (1,000)
- 1 cup of food scraps (fruits, veggies, egg shells, coffee grounds. NO garlic, onions, or hot peppers). I collect them in my countertop compost pail with carbon filter.
- 4 bricks
Here’s how this bin works: The worms and the composting happen in one bin (tote). When it gets full, the lid is removed, and the second (empty) bin is placed right on top of the compost surface of the bottom (full) bin.
Bedding and food are added to the new bin on top. After 2-3 months the worms will migrate up through the holes to the new bin. The bottom bin should be straight-up worm castings.
This philosophy seems to be way less work to harvest the castings than the single bin, so we just had to give it a try. I hope to have castings before spring planting!
How to Build this Worm Bin
1. We drilled about 50 holes in the bottom of each bin using a 1/4″ drill bit. This is for drainage and through which the worms will migrate upward to the empty bin.
2. Next we used the 1/8″ drill bit to drill about 60 ventilation holes just under the top edge. We also drilled about 50 ventilation holes in ONE of the lids.
3. We added HALF of our shredded office and newspaper, moistening it with the spray bottle. It should feel like a wrung out sponge. This is the bedding.
4. Then we added the worms. In our case, we were dumping in the contents of the old bin, so the worms went in with some castings and food scraps. You can add a few handfuls of loose garden soil or leaves if desired, but it isn’t necessary.
5. Now 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. 55-75 degrees is ideal. We keep ours in the attached garage.
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 (with holes).
10. When you go to feed the worms, pull away the shredded paper on top, pour in the cup of food, then replace the shredded paper so all food is covered.
Worm Bin Care
Only feed the worms about 1 cup of food each week for the first few months. As the worms look bigger and more numerous, you can increase the amount of food scraps you give them each week.
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 onto the bottom lid, this 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.
If your bin gets fruit flies or mites, the problem is usually related to too much food being added too fast. Just hold back from feeding them for a month or so to let things balance out.
Learn better by video? Watch me make my worm bin.
Need more ideas for building soil in the permaculture garden?
Click here to get your 19-page Guide to Organic Soil Amendments!
- 7 Ways to Improve Soil Quality
- Mulching in the Permaculture Garden
- Transitioning to a No-Till Garden
Would you like to learn more about improving the biodiversity of your garden, reducing maintenance, and increasing yield?
You’ll find loads of information just like this in my book, The Suburban Micro-Farm.
Worm castings are an easy, inexpensive, and important fertilizer for the garden. Will you build a worm bin this year?