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Monday, December 27, 2021

Worm Castings 101

Original Article:

by Rebekah White

Composting with worms is one of the best ways to create your own fertile, nutritious soil – even if you don’t have a lot of room outdoors for a full-fledged compost bin. You can get rid of all kinds of garden waste as well as kitchen debris, like vegetable peelings.

Plus, worm composting helps free up space in the county landfill (a win for the environment!) and provides you with free soil for your garden. What’s not to love?

By photography taken by Christophe.Finot – Own work, CC BY-SA 3.0, Link

I started worm composting long before I ever had an outdoor compost bin. It was a great way to compost when I was still renting a house and didn’t have my own property where I had free reign to do whatever I wanted.

Today, I still continue worm composting (vermicomposting) even though I have a large outdoor compost pile. It’s a great way to keep the composting action going even during the dead of winter – and as an added bonus, I don’t have to step outside when it’s -20 outside to do so, either!

Here’s everything you need to know about worm composting and its byproduct, worm castings.

Starting a Worm Composting Bin

Buy Worms

To start, you’re going to need to find some worms.

You won’t want to use any old worms, though. Nightcrawlers won’t do the trick. These creatures have to tunnel through the dirt to eat, and they won’t be able to survive on vegetable waste alone.

Instead, you’ll need to get some redworms, which you can buy online. These worms feed primarily on food waste, and will make quick work of your kitchen debris.

Usually, you’ll need about a pound of red worms for every half pound per day of food waste. If you aren’t sure how much food waste you produce, monitor it for one week and take careful notes.

It might not seem like you have enough worms at first – and to be fair, many vermicomposting exports recommend under-populating your bin at first until they have time to adjust.

However, once your worm farm gets going, the red worms will begin to produce, and you’ll have more worms than you know what to do with!

Get a Bin

Next, you need to invest in a bin for your worm compost. You can buy a specialty worm farm container, or you can build your own.

Size here matters – you’ll want something that is at a depth of about 8-12 inches. You can use wood or plastic. We use repurposed Rubbermaid tubs that we’ve repurposed into vermicomposting bins.

Your worms won’t have a lot of requirements – just keep in mind that they like plenty of moisture, and dislike light. Your container needs to be opaque (clear totes won’t do the trick). The bin should also have a few holes for drainage.

Set Your Bin Up

Once you have your bins, go ahead and get them in position. Some people put them in basements, while others keep them outside, in a garage, or under a sink.

Any of these settings work just fine, but ideally, your worm compost should be located somewhere in which the temperatures hover between 40 and 80 degrees F (between 4 and 26 C). Red worms like temperatures of around 55 to 77 degrees F (12 to 25 C).

If you have harsh winters, you can’t keep your red worms outside during this time. You’ll need to bring them in. Keep in mind that worms aren’t fond of lots of vibrations or loud noises, either, so it might make sense to keep your worms out of high-traffic locations.

Next, fill your bins about one-third full with bedding material. Just soak some shredded cardboard or newspaper, and make sure it’s really soaked. Worms like about 75% water in their environment.

Some people recommend adding manure to the pile, but this is not advised. You’re not building the compost for the worms ahead of time – they’ll take care of all the composting action.

You just need to provide them with a home. Adding manure will heat up your composting bin, and can cook your worms.

Once you’ve soaked your bedding, make sure it’s moist though not dripping wet. Add it to the compost bin with some sawdust or fine sand. The grit will help your worms grind up their food.

Add Your Worms

Now it’s time to introduce your worms to their new home! To do this, you will dig down into the center of the bedding pile.

Place your worms there rather than just tossing them on top of the bedding. Add your lid, and leave the worms alone for one week. They’ll start feeding on the bedding. You can begin feeding them after about one week.

Feed Your Worms

Once your worms have acclimated to their new home, you can start feeding them food scraps. You can feed them just about anything – I’ll give you some recommendations below.

Just avoid things like bones, meat, and dairy products, as these will make your bin smell and can also attract pests like flies and rodents.

This might sound obvious, but avoid adding things like aluminum foil, plastic, and glass to your bin. While you can certainly use paper as bedding, you will want to avoid using any paper that has colored print, as some inks can be toxic to words. Avoid rubber and sponge, too.

Usually, your worms will only need to be fed about once a week in small amounts (about the size of a coffee can). You may want to chop the material up so that it’s easier for your worms to eat.

As you feed your worms, check on the quality of the compost. If the bedding is sopping wet, add some more bedding to soak up the extra water.

If it’s too dry, moisten it with a spray bottle. Remember, you don’t need to do much to maintain your bedding. Once it’s brown and earthy looking, it’s ready to be used!

Harvesting and Using Worm Castings

After all that hard work (not really!) maintaining your worm compost, it’s time to use those worm castings. “Worm casting” is simply the name given to the compost created by your worms.

Your compost will be brown and earth-like when it’s ready to be used. It will look much like fertile, compost-rich soil. You can remove your castings as often as every two and a half months, or as infrequently as every six months.

How often you harvest castings will depend largely on how many worms you have, and how much food you give them.

To harvest, dump the bin’s contents onto a plastic sheet. Remove the worms (this is a great task for kids!) by hand and keep a bit of the compost to mix back in with the new bedding and the worms.

If you don’t want to dump out the entire bin, you can also just move the contents to one side of the bin. Push any partially decomposed materials to the side, then place some food atop the matter. Replace the lid and leave it alone for a week or two. The worms will migrate to the new food.

Then, you can harvest the aged compost from the bin.

You can use your worm castings anywhere in your garden. Use them as fresh compost when you’re planting or to amend garden soil.

You can also make a “worm tea” out of the compost by soaking it in water for a few days. This can be applied as a foliar spray to your plants whenever they need a dose of nutrients.
Common Worm Composting Problems – and How to Fix Them

Fruit Flies

Although I’ve been vermicomposting for quite some time, I’m not sure I’ll ever be able to get rid of my problems with fruit flies! These are super common around vermicomposting bins, and usually result from overfeeding your worms (oops).

Try not to overload your worms with too much food. You can add more bedding if the compost is too wet, or you might consider repositioning your compost bin so that the flies won’t be aggravating to you when they appear, either.

There are fruit fly traps you can use, too, but often, these solutions are enough to take care of the problem on their own.


Very rarely does a vermicomposting bin stink – but if it does start to smell, there’s an easy way to fix it. You need to stop feeding your worms so much!

Usually, odors result from too much food sitting around. If the worms don’t have enough time to eat through all the food, it’s going to start to rot.

The easy way to rectify this situation is to stop adding food until the worms have broken down what they’ve already eaten. However, you should also avoid adding greasy or meaty foods, which shouldn’t be added to a worm composting bin because they will rot and smell.

If your compost still stinks, try stirring it. This will let more air in and will reduce odors. You can check the drainage of your bin, too, since odor problems can result if there is too much water in the compost bin.

Escapee Worms

This isn’t all that common, but sometimes, worms will try to escape from your compost if the mixture is too acidic. You might notice worms moving out of the bedding or sides of the bin.

This can happen if you are adding lots of acidic food, like orange peels. To rectify the problem, add some more alkaline ingredients and simply reduce the amount of acidic matter you are putting in the bin.

What to Feed Your Worms for the Best Worm Castings

If you’re used to having a regular compost bin outside, then adding material to your worm compost shouldn’t be too much of a change. In general, if it’s safe for a compost bin, it’s safe for your worms.

Some of the best foods to give your worms include:
✅ Coffee grounds ✅ Egg cartons
✅ Paper ✅ Dry leaves
✅ Carrots ✅ Melon rinds
✅ Lettuce ✅ Fruit peels (avoid citrus)
✅ Teabags ✅ Cereal
✅ Plain pasta ✅ Bread
✅ Cucumbers ✅ Squash
✅ Cornmeal

You might want to avoid potatoes and potato peels, onions, and meat and dairy. These all break down slowly, and will stink up your compost pile.

If you aren’t sure what to feed your worms, just keep an eye on what’s left when you go to feed them each week. Like children, they’ll leave the foods they don’t like completely untouched!

Worm Castings FAQ

How do you use worm castings?

You can use worm castings in a variety of ways. They can be used on potted plants, directly in your garden when you plant, or as a foliar spray (when brewed into a compost tea).

One of my favorite ways to use worm castings is as a side dressing. Simply place a handful of castings at your plant’s base, then water. Your plants will soak up tons of beneficial nutrients. It’s especially helpful when your plants are putting on fruit.

What worms are used for composting?

You should only use red worms, also known as red wigglers, in your compost bin. Sometimes, these are also referred to as manure worms. They thrive in decomposing matter and are smaller than nightcrawlers. As the name implies, they are also bright red or red-brown in color.
How much castings do worms produce?

Interestingly, worms can eat their weight in soil every day! Two thousand red worms, when housed in a vermicomposting bin, can produce more than seven pounds of castings – in just one month. That’s pretty impressive!

How many worms do you need to start a worm farm?

To start a worm farm for composting, you will want to start with about half a pound of worms per square foot. Start with fewer worms than you think you might need, as they will reproduce rapidly once they begin to eat.

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