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Vermicomposting: How Many Worms Are Needed?

Vermicomposting: How Many Worms Are Needed?

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Paul Brown

Vermicomposting is the use of earthworms to increase the speed of the composting process to ensure a higher-quality compost that is beneficial to plants and gardens. The worms produce compost by digesting the matter and excreting it as nutritious worm castings called vermicast. But the number of worms does play a role in how much vermicast is produced.

How many worms are needed to vermicompost? A good rule of thumb is one pound of worms per square feet of the bin being used. Another way to calculate it is one pound of worms per pound of food waste. There are roughly 1000 mature worms in a pound.

But there are a lot of considerations that come into play when deciding how many red wigglers you need. This article will outline many aspects that you will want to keep in mind, some directly related and some indirectly. Feel free to jump to the section you are most interested in.

While it may not seem that each of these is related to the number of red wigglers that you need to have, each of them plays a role. For example, the type of bin you choose will influence how many worms you can realistically maintain. Understanding the benefits of vermicomposting will help you decide how much time and effort you want to put into this project and as a result, the number of wigglers you’ll need to do that. So consider all of the factors in your decisionmaking so that you can use the right number of worms for your specific project.

I’ve also included some basics on vermicomposting just in case you are new to the process but we have tons of other articles on this topic as well.

Okay, with that out of the way, let’s get to it!

How Many Worms Are Needed For Vermicomposting?

Deciding how many worms you need will depend on how you want to approach it. You can, for example:

  • Order worms based on how much space you have in your bin, or
  • Order enough worms needed to meet your food waste needs

Number of Worms Based On Size Of Bin

When purchasing red wigglers locally, you’ll probably find farmers who sell them by the pound. A good rule of thumb for determining how many you need is one pound of worms per square foot of surface area. But there are two important caveats to this traditional approach to calculating need.

First, red wigglers can multiply quickly in a healthy environment. If you size the population to the size of the bin then you need to be prepared to regularly transplant some of them to another bin so that you do not overpopulate it.

Second, you need to make sure that you can supply a steady amount of food to meet their feeding demands. Five pounds of worms for a huge bin sounds great until you realize that you cannot produce enough food scraps to feed them.

Number Of Worms Based On Quantity Of Food Waste

Another approach is to purchase worms based on the amount of food scraps that are regularly available. This is generally a more sound approach. Red wigglers can eat about half their weight of food each day, so if you have one pound of worms, you’ll want to make sure to feed them around one-half pound of food scraps each day. It doesn’t have to be exact but this is a good rule of thumb.

There are roughly 1,000 mature composting worms in one pound, so if you had four pounds of food waste, you’d want two pounds or 2,000 worms.

Now, I never did this. It feels too much like work. But this is a standard formula for calculating your expected food waste and bin size:

To determine how much food waste a household goes through, collect all of your food scraps for one week and then weigh it. You can figure on needing to provide one square foot of surface area per pound of food. 

A one to the two-person family will typically produce about four pounds of food waste in a given week while a larger family will produce up to six and a half pounds of food waste. 

You would just need to make sure that you had a bin large enough to accommodate the worms purchased along with room for them to populate. Again, I recommend starting small with 500 worms or less, learning how to maintain a healthy bin and their feeding habits, and grow from there. Unless you getting into commercial vermicomposting, there is no need to turn a fun project into a stressful event.

A Better Solution

You can also buy composting worms on Amazon, for example, by the number of worms instead of by the pound. This makes it a little easier to determine how many to get, in my opinion.

I actually recommend starting off with a smaller number of worms such as 250 or 500 and growing your worm farm from there. This will allow you to adjust your food supply and bin space to meet the needs of your worms as they grow and populate. I just find this a little easier to wrap my head around than the traditional pound formulas. Click here for composting worm pricing and options (link to Amazon).

Can There Be Too Many Worms In Compost?

When starting out a compost bin, it is a good idea to get the right number of worms for the food waste they produce in order to avoid overfeeding the worms or not having enough food for them to eat

It’s worth noting that red wigglers are able to regulate their population to suit the environment they are in. If there is not enough food in the compost bin or enough space, they will either slow down their reproduction and maintain their population level or the adult worms will begin to die off to make room for the babies. Click here to read Why Are My Red Wigglers So Small.

If you suspect that you have too many worms in your bin, you can either let the worms sort it out amongst themselves or move some of the worms to another bin.

Of course, another option can be to move all the worms into a bigger bin so that they have enough space to work.

Different Types Of Composting Worms

It’s important to understand the distinction between these two species of earthworm:

  • Red wigglers
  • European nightcrawler

These two worms are very similar and people often want to have them mixed together in a worm bin. Click here to better understand why you may not want to though.

The red wiggler is smaller and less muscular than other worms. These worms reproduce quickly and like temperatures of moderate temperatures so they tend to migrate towards the surface.

While the red wigglers stick towards the top, the European nightcrawlers like to be further down. They burrow deep and are great for gardens because they aerate the soil as they tunnel and deposit nutrient-rich castings deep into the soil.

For your vermicompost bin, you are going to want to use red wigglers. There are a few other species that are appropriate for worm bins but they are less common and not as readily available. Red wiggler worms, on the other hand, can be purchased online or locally pretty easily.

Can Worms Found In Someone’s Yard Be Used For Vermicomposting?

These are usually not what you want.

Regular earthworms need to be able to burrow deep down into the soil. They are not suitable for the shallow nature of worm bins. Worms used for vermicomposting are worms that prefer to burrow in shallow soil (Red Wigglers!)

What Kind Of Bin Should Be Used for Vermicomposting?

The truth is, just about any type of bin should work as long as it has a way to drain and sufficient air holes. However, when kept outdoors, a metal bin will eventually begin to rust, and a wooden bin can start to decay. Also, wooden bins made out of cedar or redwood can actually harm the worms.

Opting for plastic is usually the best option most people choose. You can purchase a ready-to-go worm bin on Amazon like this one or make one yourself. An old Rubbermaid container can even work. Whatever bin you use, it does not need to be very deep. Red worms live and eat in the top six to eight inches of the soil.

What Kind of Foods Can Worms Eat?

Just about anything that is biodegradable can be placed in a vermicomposting bin, however, avoid meat, fat, and bones because they are harder for the worms to digest and can produce an odor while the worms are working on them. This order can attract rats.

Here is a list of foods that are safe for the worms to eat:

  • Fruits
  • Vegetables
  • Squash
  • Pumpkin
  • Eggshells
  • Bread
  • Pasta
  • Coffee grounds
  • Grains

They can even be fed paper and cardboard, tea bags, hair, lawn clippings, and animal manure (not dog or cat)

Here are other foods that should be avoided

  • Salty foods
  • Citrus
  • Spicy foods
  • Oils
  • Foods with preservatives
  • Dairy

Some Tips for Feeding Your Vermicomposting Worms

Size. The smaller the matter, the easier and faster the worms will be able to compost it. A chopped up apple, for example, will be easier for them to consume than a whole one.

Color. It is good to keep a nice balance between browns and greens. Browns and greens are nicknames for different types of organic matter to use in composting.

  • Browns are high in carbohydrates and carbon, which supply the energy that a lot of soil organisms need to survive. These carbon foods also help to absorb bad odors and help prevent organic nitrogen in the compost from escaping by evaporation.
  • Greens are high in nitrogen and protein. These foods help the micro herd to breed and multiply. A good way for someone to test if their organic matter is brown or green is to wet it down, wait a few days and if it stinks, it’s green, and if not, then it’s brown.

Feeding Worms Too Much

Worms can eat a lot. In fact, as we mentioned earlier, they can actually eat about half their weight in food scraps, but it is possible to overfeed them, which will then lead to issues.

Here are some consequences of feeding worms too much waste:

  • Acidity – An excess of food and too many acidic foods can cause a low pH, which can put worms at risk of dying.
  • Odor – If there is too much food leftover in a bin that isn’t being broken down, that food will begin to rot, which then will lead to a stenchy bin. Bins should have an earthy smell.
  • Pests – If there is too much food, that can draw in unwanted pests to the bin.
  • Excess moisture – Some moisture is okay for a compost bin, but too much moisture caused by an excess of food can result in some problems.

Excess food can be frozen and saved for another feeding.

Why Worms Try To Crawl Away From The Compost Bin

It is normal for a few worms to try to escape their bin, especially if they are new to the environment, but if someone is noticing clumps of worms repeatedly trying to escape, then there may be some problems within the bin.

There are several reasons as to why worms will try to escape their bins. Reasons include:

  • Need more oxygen
  • Too much moisture
  • New baby worms
  • Recent change
  • pH level is off

Need More Oxygen

Worms actually breathe through their skin, so if they are not receiving enough oxygen, they will try to find more oxygen by escaping.

A lack of oxygen in a compost bin can be caused by:

  • Poor ventilation
  • Overfeeding
  • Material dumped on top of them
  • Poor bin design
  • Too wet

Poor Ventilation can be as simple as not having enough air holes. These not only provide a means for fresh air, they also help to regulate moisture levels in the bin so make sure you have enough.

To avoid overfeeding, make sure the worms are going through most of the food scraps before giving them more. Don’t keep adding food if they don’t seem to be eating it. Be sure to read My Worms Are Not Eating: Solving Red Wiggler Feeding Issues.

Compost bins also need to have proper drainage to allow excess liquid to drain away from the bedding. Read Why Your Worm Farm is Not Producing Liquid.

Too Much Moisture

When there is too much moisture in a compost bin, the worms can drown, which will make them want to crawl away to safety. Having too much moisture can also cause mold and mildew to grow.

The worm bedding should be moist but have the consistency of a wrung-out sponge. To check for proper moisture, simply squeeze some of the worm bedding in your hand, and if water comes out, there is too much moisture.

To fix this add some dry bedding to the bin to soak it up. You can use shredded paper, peat moss, shredded cardboard, or coconut coir.

Ease off on the water-rich foods until the moisture level returns to normal. Examples include melon, pureed food, or thawed frozen fruit.

New Baby Worms

Why are my red wigglers small?

Worms reproduce, and when they reproduce, hundreds to thousands of baby worms hatch, which can result in some of the adult worms feeling overcrowded, so they begin to find space elsewhere.

Worms can typically balance out their population, so overpopulation can either be ignored, or you can remove those escaping worms and move them to their own bin.

Recent Change

If the worms have been in the same environment for a while and are suddenly trying to escape, check to see if you have made any recent changes that may have caused them to want to leave.

Changes could be new bedding, adding new worms, or changing the foods they are used to eating.

If you notice your worms suddenly escaping and believe it is food-related, remove uneaten food items and start over. They won’t starve if you take away their food for a day or two.

pH Level Is Off

It’s a good idea to have a pH meter so that you can make sure your bin is in balance. We have a list of recommended composting products that include an inexpensive pH meter you may be interested in. The bin should be at a healthy neutral pH level of six to seven.

If the pH level is too high, adding some crushed eggshells to the bin can help lower the pH level and also add grit that helps the worms digest the food.

Having acidic, salty, or oily foods like tomatoes, potato chips, and citrus can help throw off the pH level of the bin so avoid those if you are seeing problems.

Quick Fix for Getting Your Worms to Stay in the Bin

If you have done all of the above steps to try to keep the worms in their bin but they are still trying to escape, shine a light on the situation, literally.

Worms do not like bright light, so shining a light on them will make them want to dig their way back down into the soil to avoid the light. This is a temporary solution. Don’t leave a light on them constantly. Just while you are getting their bin back in balance.

Also, adding dry bedding on top of the surface contents of the bin will make the worms dig back down to the moist layer of the bin.

Benefits Of Vermicomposting For Plants

Vermicomposting is used for converting waste into natural plant fertilizer. The most important aspect of this form of composting using worms is that it can be 100% organic. No chemicals required and as long as you are mindful of what you feed them, you can truly create an organic compost.

Another benefit is that it is extremely nutrient-rich. Vermicompost produces a product that is naturally made to benefit plants in different ways. A primary benefit is that the nutrients absorb easily and are quickly available to the plants.

The worm mucus that is found in vermicompost does not wash away easily. This gives plants longer to absorb the nutrients unlike many chemical fertilizers (source).

As the compost passes through the body of the worms, it becomes enriched with microbes and bacteria. These micro-organisms help the plants to become more disease resistant and repel pests.

Vermicompost enhances plant growth-regulating hormones that can help the plants grow and become healthier (source). As the plants become healthier, the need for pesticides is reduced.

Vermicompost can hold up to many times its weight in water which can really help out plants during a dry spell. This is especially beneficial in sandy soils where water retention can be challenging.

How To Set Up A Vermicompost Bin

Once you figure out the size of the bin you need and the number of worms needed, you can begin to set up your own vermicompost bin and let the worms get to work. Whether you build your own bin or buy one ready-to-go like this one (link to Amazon), getting started is pretty darn simple.

The first step is to create bedding at the bottom of the bin. Composting worms like newspaper strips. These are a favorite for bedding.

  • Tear newspaper into ½” to 1” strips
  • Place the strips into a plastic bag and add water until they feel slightly damp
  • Add the strips to the bin
  • Sprinkle two to four cups of soil to the bin

Once the bin is set up, the worms can be added, and food scraps can be dispersed throughout the bin under the bedding. A full sheet of dry newspaper can be added on top of the bedding to help maintain a moisture balance, prevent odors, and keep fruit flies out.

The bin should be covered by plastic, wood, or cloth to keep the worms in and pests out. Holes should be drilled around the edges of the lid for proper ventilation or the lid can be left partially ajar.

Bedding should be regularly checked for dryness and sprayed with water if it is not moist enough. If bedding becomes too wet, drier bedding can be added to soak up the excess moisture.

The bedding should be fluffed about once a week to ensure that the worms are getting enough air. This is a pretty simple process. Don’t overthink it and don’t worry that you are going to mess something up. Keep an eye on things and adjust as needed.


Determining how many worms you need depends on how big your bin is and how many food items you plan to compost. I recommend starting small and building from there. Beginning your vermicomposting adventures with a huge number of worms and a very large bin can feel overwhelming.

There is no need to make this a source of stress. Let it be a journey of discovery. Purchase a couple of hundred worms, learn how to keep the bin in balance and how much they eat and go from there. You can add more worms later if you but they will multiply to meet the space you provide them Keep them healthy and happy and you will have a source of continuously replenished nutrients for your garden or plants.