Compost Magazine

Composting tips, advice and science.

Cartoon image of worm in a garden holding a magnifying glass.

Should You Add Worms to Your Compost Bin? Here’s What The Science and The Experts Say…

Did you know that a worm can digest half its own body weight in a day?

These little wonders work really hard for you in your compost heap. 

So naturally, you’ll be wondering if you should add worms to your compost bin to reap some of their benefits. 

However, you don’t usually need to add worms to your compost bin, as they tend to show up naturally over time.

(I am talking about regular composting here, not vermicomposting!)

I’ve found that they even appear in bins where you wouldn’t expect them to – such as in my experimental small bins, raised up on a wooden table on a concrete floor in a greenhouse.

What’s more, while worms can help the composting process, that composting will take place whether or not you have worms in your compost. 

Still, adding worms can speed it up and improve the quality of the final compost.

Plus, sometimes you won’t have worms in your area, in which case adding them is the only way to let them improve your compost. 

However, there are a few things to know first.

For example, it’s key to know when to add worms to your bin if you want them to survive, and to know what type of worms to add

What role do worms play in the compost bin?

Your compost bin is like a busy city, with a ton of organisms each playing their own role. 

(Or, given the death and destruction that goes on as organism eats organism, maybe a war zone would be a better description!)

These organisms include bacteria, fungi and even viruses!

Worms are part of another group of creatures that make up the compost food web – physical decomposers. 

They are multi-tasking little creatures who: 

  1. aerate the compost
  2. help eliminate pathogens
  3. help eliminate antibiotic-resistant genes
  4. reduce the quantity of heavy metals in compost
  5. increase nutrient availability in compost 
  6. increase the ability of compost to hold water.

See: Why You Need Worms in Your Compost for more on the benefits of worms. 

Not everything is beneficial – worms do seem to reduce the total amount of compost. 

Experts also seem divided on their impact on nutrients such as nitrogen. 

However, some studies do suggest worms help combat nitrogen loss in composting. 

It’s worth noting that most of these studies look at vermicomposting, rather than adding worms to compost after it has cooled down.

How do worms get in the compost bin naturally?

Worms on compost bin side.
Here’s the worms that greeted me one night on the edge of my HotBin! (I don’t usually see this many!)

Worms may get into your compost via worm cocoons or be attracted to the compost by decomposing material. 

Worms cocoons are in: 

  • the soil stuck to weeds 
  • in manure you add
  • on other organic material you add.

As organic matter decomposes in the bin, it also attracts worms looking for a source of food and a comfortable habitat.

(Some sources state that worms don’t eat organic material directly, but instead feed on the microbes that grow on it.) 

Some worms are attracted by the carbon dioxide released by rotting organic material, although I can’t find any sources that confirming this for compost worms.

Still, as long as there’s an opening somewhere in the bin, and the bin is based on the ground, worms will usually enter naturally. 

There are two exceptions. 

One is if the compost bin is raised up or indoors. 

(Although even then they sometimes find their way in.) 

The second is if there are no worms in your area. 

What are the right conditions for worms in compost bins?

Theoretically, at least, there are quite a few conditions that need to be right for worms. 

Temperature

We’re often rightly warned that compost worms will not survive freezing conditions. 

However, it does depend on the species. 

According to one source, the most commonly used worm, Eisenia fetida (known as red wrigglers among many other names), produces an anti-freeze

However, most vermicomposters will tell you that freezing will kill most of them. 

Research agrees, finding that red wrigglers die when exposed to low temperatures. 

Other types of worms proved hardier. 

That’s potentially another reason to let local worms used to your climate populate your compost bin rather than add purchased worms. 

However, you can protect and encourage your worms to keep working on your compost pile by using an insulated compost bin or by keeping the compost pile with a material like straw. 

You shouldn’t let them get too hot either.

Most earthworms can only tolerate a maximum temperature of 30C, although some compost worms, including Eisenia Fetida, have evolved to tolerate higher temperatures.

For these worms, ideal temperatures are between 13C/55 F and 35C/77F.

That means that a hot compost heap has to cool down before worms can survive in it. 

Sufficient air

Just like us, worms need to breathe.

(Intriguingly, many worms can survive submerged for significant periods of time – but only if the water is oxygenated.) 

If you haven’t aerated your compost for some time, it may be worth doing so to ensure oxygen levels are sufficient.

Acidity

Worms can typically survive a wide range of pH levels. 

However, they are sensitive to changes in acidity, and can find it difficult to extract food at higher acidic levels. 

What’s more, just because they can survive a wide range of acidity levels doesn’t mean they will hang around!

Uncle Jim’s Worm Farm recommends an ideal acidity level of between 6 and 7.

However, expert Heather Gorringe of Wriggly Wigglers, who has 30 years of experience of breeding and managing worms, told me:

In terms of acidity, this is only a problem if you are adding all really acidic material such as lemons and onions, so it’s not really relevant in a garden composter (sometimes relevant in a wormery designed for dealing with kitchen waste).

Rather than starting to control acidity with lime or ash, it’s probably best to just let the compost stabilize. 

Moisture

Worms require some level of moisture, as they breathe through their skin. 

They also lose about 20% of the moisture in their body every day. 

However, you don’t want it too wet. 

Just as with regular composting, the ideal compost material for worms should feel like a wrung-out sponge. 

Salts

Worms can’t tolerate high levels of salts

Salts are usually high at the start of the composting process but gradually decrease over time. 

Again, though, Heather told us not to worry too much about this.

How to encourage worms to get into the compost bin?

Worms on coffee grounds.
Worms seem to be little caffeine addicts!

Cornell University suggests adding a layer of coffee grounds to the bottom of your bin to attract worms.

It’s also worth ensuring that the compost is moist, as worms do not like dry conditions. 

However, the bin shouldn’t be too wet, as this can force air out of the compost – and worms also need to breathe. 

As compost bins should be moist anyway, that hopefully won’t require any extra action!

Heather suggested taking care to layer the bin (which also helps aerate it):

A key point is to layer the material you are composting (maybe grass cuttings, then layer of cardboard, then layer of leaves, then layer of green and kitchen waste and so on).

Some people use a few drainage pipes or similar placed vertically and this is a brilliant way of ensuring air.

(If you’re interested in trying this out, see our guide to making a simple compost bin with passive aeration.)

She also suggested taking care with where you site the bin:

If you can site your composter on the soil that is a real advantage for the compost and the worms.

The worms will aim to stay where the easiest food source is with the best conditions so they will naturally migrate into the compost.

Four ways to add worms to your compost bin (three are free!)

A pair of hands cup compost worms above dark compost.

Dead keen to get more worms in your compost? Here’s four methods to try.

  1. Add soil or compost from another pile: By adding a handful of soil, you are likely adding worm eggs to the compost bin. It will take a while, but eventually, they will hatch and breed. Don’t add too much, as the soil itself will not contribute much to the compost. 
  2. Add manure: Manure often contains tons of worms. Add a few handfuls of manure and there is a fair chance you will be adding worms too.
  3. Transfer from other bins: If you have other compost bins – or a friend has one – in a more advanced stage, you can transfer worms from these to the new bins. 
  4. Purchase worms. If you can’t wait for worms to populate the compost heap, or really want to speed the process up, you can order some. 

When you do add worms to your compost, make holes in different parts of your compost, and add about 50 in each hole. 

(You don’t need to be exact ;)) 

What types of worms should you add to your bin?

It’s really important to add worms that are suited for composting, not worms that prefer to live in soil.

There are many hundreds of types of worms. 

The big, long fat ones you dig up in the garden prefer to live deep in the garden soil and are are not cut out for composting. 

The ones you want are surface litter worms, which, as the name suggests, love breaking down organic material in compost heaps and worm bins.

We’ve already mentioned Eisena Fetida, aka the Red Wriggler. 

It is commonly considered to be the best compost worm available. 

One study suggested that the African nightcrawler produced compost with higher nutrients. 

Still, the worms you can purchase will depend on both your climate (African nightcrawlers are not well suited to temperate climates) and availability in your area. 

Another option is to buy a mixture of worms. 

For example, Wiggly Wigglers sells a mixture of different compost worms, as different worms work better in slightly different conditions. 

You should also be careful not to add any worms that could be harmful to your local environment. 

In the US, some composters have found the invasive Asian Jumping Worm in their worm orders. 

These worms can be very damaging to forest floors – so always be careful to order from a reputable supplier!

When should you add worms to a compost bin?

Given all the factors we’ve discussed about when to add worms, you might think it would be difficult to judge when they should be added. 

However, it can be easy to overthink it. 

In fact, Heather told us:

As long as it’s not hot in there –  add the worms.

We suggest putting them into some bedding (like coir) and placing them into a corner so that they can establish in the cool then start to work in

Should you add worms to compost tumblers?

Vermicomposters recommend you DON’T add worms to compost tumblers

That’s because worms really don’t like being swung around a barrel every few days!

However, once the compost has started to mature, and you are no longer turning it, it should be fine. 

Chances are you will have removed it from the Tumbler by this stage anyway!

How do you protect the worms in your compost heap?

A toad consumes a worm in a mossy garden.

Protecting them from predators

Worms may be wonderful, but they are considered a delicacy by many other creatures. 

These include creatures like moles, ants, centipedes, snakes, toads, and more.

This is all, of course, part of the natural food web, and you can’t expect to protect worms from everything. 

Still, one of the benefits of a compact compost bin is its ability to deter some predators.

Covering over entries to your compost bin with wire mesh can do wonders to protect your worms from larger animals like hedgehogs. 

Remember, you don’t need to add worms

While worms improve the compost, composting will take place with or without them. 

And, most of the time, worms will appear of their own accord. 

If they don’t, it might be because the conditions aren’t yet right for them. 

It may just be a case of waiting for the compost to mature so worms can enter. 

You can also check the conditions of the compost. Ensure that it’s not too hot, wet, or dry, and consider aerating the compost.

With patience, you’ll soon find worms working their magic in your compost bin!

Watch

Here’s an amazing timelapse video of red wrigglers…

YouTube video player

Read next…

How to Build A DIY Worm Bin In 20 Minutes or Less
How Fast-Evolving Worms Remove Metal From Compost
How Worms Work Their Magic In Compost
Worms Produce Superior Compost Say Researchers

External resources

Fauziah S.H., Agamuthu P., (2009) Sustainable Household Organic Waste Management via Vermicomposting

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