How to Correctly Feed Compost Worms: What, When, How and How Much

by Matt Gibson

Worm composting, also called vermicomposting, is a great way to use kitchen scraps to create a nutrient-rich compost to feed your garden and keep it producing year-round. In a large container, simply shred some newspaper and leaves from your yard to create a nice loose base, then add in red wiggler worms, officially known as Eisenia fetida, and some moisture. Then you’ll be ready to start your very own vermicomposting headquarters that will create your own compost all year long. Once the worms’ environment has been created, it’s time to learn what to feed your worms, when to feed them, and how much food they will need to create the perfect nutrient-packed compost that will help you condition the soil of your garden year in and year out.

What Your Composting Worms Should Eat and Not Eat

Worms have voracious appetites, but they don’t actually eat the waste food that you put into the soil to feed them with as is. Instead, they wait for that waste food to become covered in microbial communities. In fact, your worms’ main source of nutrition comes from the microorganisms that grow in abundance on organic fruit and vegetable waste. That’s why instead of devouring the scraps that you throw in to the soil immediately, your worms will wait around until microbes begin to flourish on the surface of the food scraps. Once the microbial content of the food is high enough, dinner is served, and the food is ready for your compost buddies to eat their fill. A word of caution, however—don’t just throw any old kitchen scraps into the compost bin and hope for the best. Keep reading, and let’s dive into what you don’t want to feed them.

Do not feed your worms fatty or processed foods, such as meat or dairy products. These types of kitchen scraps will cause strong odors when they decompose that you won’t want stinking up your home. Fatty or processed food scraps will also disturb the delicate ecosystem that you’ve worked so hard to create in your composting bin, attracting fruit flies, house flies, and other pests as well as disrupting the moisture level you’ve worked to calibrate in your composting container.

Do feed your worms organic fruit and vegetable waste, including the rinds, cores, and peelings of your favorite fruits and vegetables. Feed them crushed eggshells, coffee grounds, and coffee filters (as long as the filters are unbleached), teabags, and aged manure from vegetable-eating animals, such as rabbits, horses, and cows. Be careful not to feed your worms any manure containing deworming medication (makes sense, right?) that could kill your worms.

Citrus fruit scraps are an acceptable addition to your bin in small amounts, but make sure not to overdo it. If you eat a lot of citrus fruits, you will want to limit the amount of scraps you add from oranges, limes, lemons, and grapefruits, as the peels contain a chemical that can harm red wiggler worms in large amounts. Avoid adding salt, or any salty foods, to the compost bin. Salt is really bad for worms and can kill them if it’s present in large amounts in the compost container.

Onions are another kitchen scrap that you may want to consider just throwing away instead of adding to the compost bin to be consumed. There are conflicting reports on the web, to be sure. Some composters use onions, and some do not. The reasoning behind some gardeners leaving onions out of the mix is pretty sound. As you know, onions can stink pretty badly, especially as they decompose. However, green onions in small amounts should pose no major problem.

Avoid adding oils, such as olive oil, sesame oil, or butter into your compost. Vegetable oil is okay in small amounts, but it’s best to just avoid adding oils altogether, as oils slow down or even stop the composting process completely.

When and How Often to Feed Your Worms

It is very important not to overfeed your worms when you are first starting your vermicomposting project. Your new nematode friends will have to wait patiently while the microbial organism population builds up before they dive into dinner. Be careful not to overload the compost bin during the first couple of weeks to give your worms time to settle in to their new environment a bit. Once the environment is set and you’ve added your worms, it’s important to never let them completely run out of food to eat. Remember, their food needs to grow plenty of microorganisms before they will eat it, so you will want to cycle in new food waste every two or three days.

Check the compost bin every other day. When provisions get low and the worms are wriggling around in the last bit of food waste that you gave them, it is time to add more. Don’t worry if the worms avoid the new food waste that you just added at first. They will get to it as soon as it has grown enough microorganisms to satisfy their cravings. The size of your compost bin will determine the amount of food waste you should use each time, but typically a cup of food waste every other day will be sufficient. If the worms are not eating their food to the point that it begins to build up, simply skip a feeding or two until they start to consume the end of the food waste you provided. Overfeeding the worms and not allowing them time to eat down their food supply before adding more will lead to a stinky compost bin.

When preparing the food waste that’s headed for your compost bin, chop fruit and vegetables into the smallest pieces possible so they will decompose at a faster rate, speeding along the process. Take note of how often you notice the worms consuming their food and how much food they consume each day. Once you get to know your worms’ appetite level, you can better predict how often to feed them and how much to feed them each time. There is no perfect amount or by-the-book method, so it’s up to you to adjust feeding times and amounts as is necessary. Make sure you rotate which area of the container you place the food waste into to ensure that every worm gets plenty to eat. Put the food waste three to four inches under the top of the soil to keep it from rotting out in the open and attracting flies and other pests.

Once you get the feeding schedule down to a science, the rest of the vermicomposting process is quite easy. Simply let the worms create compost, and when the time is right, mix that compost in with the soil in your garden to pack it with nutrient-rich, fertilizing goodness that your plants will thrive in season after season. Notice the impact that composting has on the amount of trash waste that you send off at the curb each week to fill up a landfill as well—not to mention how your vermicomposting hobby lessens the number of times that you need to take out the trash to begin with. Do not add water to the worm bin unless it is severely dry to the touch. In other words, don’t add water just to make more tea. Composting requires maintaining a delicate balance in the bin, and too much water will throw that balance off significantly.

Make sure to use a drip pan underneath the compost bin to collect the compost tea. Don’t let the moniker fool you—this is not a tea that you are going to want to drink. Compost tea is probably about the rankest liquid concoction anyone could possibly create, and it’s not at all meant for consumption. Compost tea is, however, a great liquid fertilizer, so collect it, then store it in a spray bottle so you can put this useful composting byproduct to use each gardening season.

How Many Worms You Need

You’ll want to start out with about 500 to 1,000 red wiggler worms, or one to two pounds of worms total. Your compost bin should be filled with a one-to-one ratio of worms to garbage. If you started out with a different balance, don’t stress out over it. Worms tend to multiply very quickly, so you will most likely have plenty of worms in due time, even if you started with too little. In fact, red worms are known to double their population size every 90 days. If you started with far too few, it’s okay to purchase more and add them to the mix. Just sprinkle the extra worms on the top of the bin. They will distribute themselves as they swim away from the surface layer to escape the heat of the sun or grow light.

Vermicomposting is an easy, affordable way to reap major rewards for your garden. The bounty of your vermicomposting bin doesn’t stop at compost and the compost tea. The waste the worms leave behind, which is called worm castings, are excellent to feed your potted plants. Used as a soil amendment, worm castings can bring soil that is lacking in nutrients back to life and get it prepped for a season of incredible growth. Worm castings are full of nitrogen, potassium, phosphorus, and humic acids that help improve soil structure.

After you gather your supplies: a bin, shredded newspaper or leaves, and red wiggler worms, all you need to do is start saving food scraps to feed them. Now that you have the facts you need to get started with vermicomposting and care for your worms, nothing should stand in your way. You can use the vermicomposting method to take advantage of small spaces, making it a great option for apartment composting. Get ready to see major results from the additional nutrition your compost bin will give your garden.

Want to learn more about feeding compost worms?

All Things Organic covers Feeding Your Worms
Gardening Know How covers Vermicomposting Do’s And Don’ts: Care And Feeding Of Worms
Home Composting Made Easy covers Worm Composting
How Stuff Works covers How Vermicomposting Works
The Prairie Homestead covers Feeding Compost Worms: What, When, How
Uncle Jim’s Worm Farm covers How Much to Feed Composting Worms
Worm Composting Headquarters covers Feeding Your Worms