Worm Composting for the Home Gardener

By Alfred Day Decker, Permaculture Designer, Teacher, and Consultant

Some people know me as the “Moses of Urban Worm Composting in Barcelona” because a decade ago I started using worms and microorganisms to convert organic waste into a rich fertilizer for plants. Known as “vermicomposting” or simply worm composting. As a Permaculture gardener, it’s one of my favorite techniques for creating an important garden resource out of what is often considered garbage by our society.

One fateful day 10 years ago in the city centre of Barcelona, I discovered an abandoned worm composting bin on a rooftop. I opened the top to find 7 sad and dying compost worms barely alive. At that moment I realised it was my fate to learn how to do worm composting, something I had wanted to learn for a long time but had never gotten around to it.

As I walked home with my worm bin and 7 little “wrigglers”, I began asking myself what food they would need. I knew that for good composting you need to have materials with carbon and nitrogen. As I quickly learned, a worm diet of champions was all around me and I could get all the food that I wanted for free: cardboard and non-glossy newspaper from the recycling bin (sources of carbon), and food scraps from my kitchen and the local market (sources of nitrogen).

At the bottom of the worm bin I made a little bed of moist shredded newspaper and cardboard for my new friends. It’s good to avoid giving them to much nitrogen-rich food while they are settling into their new home. Compost worms are often called “Californians”, though I’ve had Catalan independentista friends say that their compost worms are from Catalunya. Regardless of where they originally come from, compost worms are different from earthworms in that they are surface feeders. You can get them from other worm composting freakies like me, or order them online (yes, in the internet age, you can receive a box of compost worms in the mail!).

These worms are like Californian stars in Hollywood movies: they don’t like the weather too hot or too cold; they eat voraciously and consume resources like gringos do; they like oxygen flow; and like Californians, they make the best lovers: compost worms spend their time either making love in hermaphroditic orgies or eating their own weight in food every day.

So, thinking of the worms as Hollywood stars, just make sure to give them the conditions they want and they will eat enormous amounts of food – which is what you want because their poop is “brown gold” for gardeners – and they will reproduce more quickly than you imagine! So keep the material in the worm bin not too wet and not too dry, not too hot and not too cold. 

So after a few days of getting acclimatised to their new home, I started giving the worms some food scraps from my kitchen. I soon developed a rhythm: I would put a thin layer of food scraps over the top of the worm bin, and then cover that with a layer of non-glossy newspaper and/or cardboard on top.

Aside from the important interaction between nitrogen and carbon materials which is essential for the composting process, the newspaper and cardboard also create air pockets where oxygen can move through the compost.

Believe it or not, worms inhale oxygen and exhale carbon dioxide just like we do…they even look like some of us!

If you keep the temperature and humidity under control, alternate layers of food scraps and newspaper/cardboard like a lasagna, it’s hard to go wrong. If the compost starts to stink that is a sign that the composting process has gone “anaerobic” (without air), there is too much humidity and not enough air, but it is easy to fix:

Just mix in a healthy amount of dry newspaper/cardboard throughout the bin until the compost material is not too wet and has more air pockets for the all-important oxygen.

People tend to get very rigid and dogmatic about how to compost. I joke in my Permaculture courses that there will probably soon be a deadly civil war over the only one true way to compost. One example is how some compost experts claim that certain foods must always be avoided from the worm bin. In my experience, as long as you don’t put too much of anyone material into the compost, and as long as rats and mice can’t get into the bin, there is no problem in putting in some bones, dairy, eggs, garlic peels, citrus peels, etc. 

When the worms eat the material in the bin and poop it out, it is a balanced and very potent all-round useful fertiliser that contains beneficial micro-organisms found in the digestive tract of the worms. This material is called “worm castings”, which is just a fancy way of saying worm poop and can be added directly into potting soil for pots and garden beds. You can also pour water through it and collect it as a “worm compost tea” which is also an absolutely fantastic fertiliser that you can water into the soil around your plants, but watch out: it’s very strong so I recommend starting slowly and diluting it 1 part compost tea to 10 parts water.

People started called me the “Moses of Urban Worm Composting in Barcelona” because I became so enthusiastic about worm composting that I built many different types of worm bins on my apartment terrace and within a year had thousands of compost worms munching away on food thrown out in the local market. One friend gave me the advice that I shouldn’t talk so much about worms if I went out on a first date with someone who wasn’t a gardener! In any case, I felt like Moses who had rescued his people – those sad little compost worms — and delivered them to the Promised Land, which in my case meant that I gave out thousands of worms to enthusiastic gardeners from all over Europe, including students from my courses who took them back to places like Sweden, Wales, and Turkey on planes and trains.

Coming back to a Permaculture principle that I mentioned in my last blog post,

“The problem is the solution”

we can see that by using “waste” materials commonly found without cost in any urban area we can easily create a rich and effective fertilizer to boost plant productivity and resistance to disease and insects.