What Worm Castings can Bring to your Soil

Forget Composting! Let Worms do all the Work.

Worm castings are an amazing soil amendment, loaded with nutrients in a form plants can use, lots of organic matter, and some other interesting and useful stuff added by the worms. They are crumbly, chocolate-brown, fluffy and fine-textured, and have the rich, sweet aroma of a forest floor. Mmm…mm, almost good enough to eat.

Well, not by me, directly, but everything living in the soil goes absolutely nuts over them and all that happy soil life will make every plant you grow the best ever: healthy, beautiful, and productive.

And the best part?

With a small initial investment for a big handful of worms, you can make as much of the amazing stuff as you want for pretty much free (compared to paying through the nose for it in plastic sacks at the garden center).

What more could any thrifty gardener want?

So, What the Heck Are Worm Castings?

Well, to put it bluntly, they are earthworm poop. Every day worms eat their own weight in dead and dying organic matter (your kitchen scraps, old leaves, shredded paper, weeds), digest it, and poop it out.

Here’s a really cool video showing some worms at work. And, unlike cow poop or other manures that can be great for your soil and plant after composting, worm poop doesn’t stink (at least most people don’t find its earthy aroma offensive) and it is safe and ready to spread in your garden or even on the soil around your houseplants immediately.

Are Worm Castings and Compost the Same?

Both compost and worm castings (which are sometimes called compost, but they are so much more I really can’t bring myself to call them compost) are made from digested organic matter, but there are some important differences.

Traditional compost is made by tiny bacteria and fungi, which break down the organic matter by dissolving its cell walls and living off the nutrients that get released(Here  is a good way to compost for your garden). Worm castings are poop that has passed through the digestive tract of an animal (earthworm), and they have some really great additional benefits compost doesn’t have.

You could think of worm castings as compost on steroids. Worm castings are higher in humus than compost, which helps the soil they are added to hold more air and more water (both really good things for soil life and plants) and helps bind more of the micronutrients in a place where plant roots will be able to take them up. They are also higher in micronutrients than compost is and deliver a much higher level of microbial activity to the soil, all of which translates into higher yields from your plants.

Don’t get me wrong, I’m not knocking compost (perish the thought), but worm castings are special! Both are important in a good soil mix.

Producing Worm Castings

Commercial vermiculture (literally, “worm growing”) operations or vermicomposting facilities use millions of worms inside massive buildings to convert tons of organic waste into piles of worm castings (and more worms), and they are a really cool part of the recycling industry.

But if you are like me, you probably only want to convert a few pounds of kitchen scraps into a handful of worm castings each week. Perfect! The great thing about vermiculture is that it works equally well at either scale!

Making Your Own Worm Castings

There are lots of snazzy home worm bins on the market, so buy one if you like, but you don’t need anything fancy to get started raising worms and harvesting worm castings, just a largish box or bin, some kitchen scraps and newspaper, and some starter worms.

A bin about two square feet and at least 8” deep (a 10- to 20-gallon storage tub like this fits the bill) is a good size for the average family if all you want to do is recycle your kitchen scraps into castings. You will want to set your bin on a tray to catch any liquid that seeps out (this is also an amazing plant food). If you want to get fancy you can use two nested bins, replacing the floor of the inner one with wire mesh, but a single bin will get you started.

Drill some holes in the bottom and sides of your bin to let the air in (worms do need to breathe) and excess moisture out.

1. Set up your bin up in an out of the way and well-ventilated place that will stay between 65°and 85°F and where a bit of odor won’t offend anyone (mostly, you’ll just smell “forest,” but occasionally things can get a bit out of whack and pee-ew!).
2. Tear newspaper into thin strips (or grab a bag of shredded white paper from the office) and put a 3”-4” layer of crumpled up strips into the bin, moistening it with a watering can until it is moist but not soggy. Leave it loose, don’t pack it down. Then toss in a couple of handfuls of garden soil.
3. Add your worms. Most people use a type of earthworm called red worms or red wigglers (Eisenia fetida) because they do a good job and thrive in worm bins. You can buy them online here. Give them a day to get settled before starting to add scraps.
4. Add kitchen scraps as available (or save them up and add every few days). Pull open a hole with a trowel or your fingers (wear a dedicated dishwashing glove if the ew-factor is too much for you) and bury them. Worms like to eat pretty much everything you do, plus a bunch of stuff you don’t like peels and cores, but go easy on the citrus and don’t put in any meat, bones, fats, or dairy products as it can cause problems (a trace in prepared foods is fine). Also, don’t overwhelm the poor wigglers with too much of any one thing at one time, as worms thrive on variety. Bury the scraps in a different place or places each time you add. During the first few weeks it is a good idea to add a handful of garden soil on top of each scrap deposit to cover it; after that, there will be plenty of castings to do the job.
5. Add a bit more shredded paper on top each time you feed your wigglers. If the bedding and scraps are wet and/or your nose detects bad things, add dry paper, which will help dry things out. If everything in bin feels dry, sprinkle the contents and the new bedding with water.
6. Once the castings start to fill up your bin it’s time to get ready for your first harvest! Start making scrap deposits only near one end of the bin, so most of the worms will congregate in that area. After 2 weeks, use a trowel to scoop out the castings from the far end of the bin. There shouldn’t be too many worms in them, and you can easily pick out and toss back any stray wigglers who didn’t take the hint. Use your harvested castings in the garden or put a little on the soil of your potted plants. Spread out the remaining castings/scraps/worm mixture and continue feeding as before.

If your worms are happy they will be making like the birds and the bees and making more worms, so at some point you may have more worms than you have scraps to feed them (if you can’t find any traces of your last deposit, you have too many worms).

At this point you need to harvest some worms and either make a second bin and start turning garden waste (and any other organic wastes you can get your hands on) into MORE castings, share your extras with someone who’d like to start a worm bin of their own, or make fried worms (I kid you not, earthworms are loaded with protein and said to be very tasty; note I said “said,” I’ve yet to try them)!

Some folks recommend dumping the extra worms into your garden, but that is a bad idea for northern gardeners, see note below.

A Note to Northern Gardeners about Earthworms

Despite their godlike reputation as being Mother Nature’s gift to gardeners (heck, my grandpa used to buy them by the pound and release them into his vegetable plot) earthworms are not native north of about the Mason-Dixon line and some types have become invasive and are causing a great deal of damage to wild ecosystems.

Most notably, earthworms are completely changing the forests in places like Minnesota, Pennsylvania, New York, and New England. The worms scavenge for every fallen leaf and twig on the forest floor, leaving only bare earth that can no longer support the growth of seedlings because it is now dry and hard, instead of being covered with a moist layer of natural mulch.

Lack of new seedlings is changing the makeup of the forests and the starving out the animals that depend on the smaller plants for food. Earthworms can only spread a short distance each year on their own so they depend on humans to move them (unknowingly in soil or on purpose by gardeners or fishermen dumping extras). So, by all means, DO go ahead and practice vermiculture and use the castings in your garden! But please avoid introducing earthworms into your garden if you don’t already have them, especially near wild forested land.

Worm Bin Sound Like Work? Be a Smart and Lazy Worm Farmer Instead

If you already have earthworms in your yard and garden soil just let them do all the work. Any organic matter you spread on the surface of the soil will slowly be pulled down and digested by them, so you can get the benefits of worm castings by simply using all your organic wastes including your kitchen scraps as mulch (spread moist scraps under a thick layer of straw or dead leaves to discourage larger scavengers and to avoid making your garden look messy). Sheet mulching (or sheet composting) not only feeds your worms so they make castings for you, it also keeps down weeds, helps conserve moisture, keeps your plants free of splashed dirt, and even reduces the risk of some plant diseases.  Here are some more tips to really super charge your soil.

So really, it’s about letting the worms do the work — and trust me, you want them to devote hours in your garden. Next time you’re ready to plant in the garden, add some worm castings. It just might make all the difference for your veggies this year.