Composting is Mother Nature’s ultimate recycling process which converts everything that was once living back into soil. We can compost a lot of organic matter in our homes and gardens, and use it to improve the quality of our soil, rather than toss it out into landfill.
For successful composting, it’s important that we use the right mix of materials. The composting process requires materials which contain both carbon (C) and nitrogen (N). The optimum ratio of carbon to nitrogen (C:N) in the final mix of compost materials needs to be between 25:1 – 30:1 parts carbon to nitrogen by weight.
The reason for this is because the composting bacteria require carbon and nitrogen in these proportions as nutrients to construct their bodies as they reproduce and multiply.
The Two Groups of Composting Materials, Greens and Browns
- Materials high in carbon are typically dry, ‘brown’ materials that rot down very slowly, such as sawdust, cardboard, dried leaves, straw, branches and other woody or fibrous materials
- Materials high in nitrogen are typically moist, ‘green’ materials that rot down very quickly, such as lawn/grass clippings, fruit and vegetable scraps, animal manures and green leafy materials.
When composting, there’s no need to worry about carbon-nitrogen ratios, just work by volume, it’s much easier.
When composting, use 1/3 ‘greens’ (nitrogen containing) materials with 2/3 ‘browns’ (dry carbon materials). In other words, add one bucket of nitrogen-rich material to every two buckets of dry carbon-containing material.
For example, 1/3 manure mixed with of any 2/3 dry carbon materials will work well to produce compost.
When composting, lay down alternating thin layers of greens and browns, and the bacteria will do the rest. The materials will break down the fastest at the bottom of the heap where the materials were placed first.
Try to use a wide variety of ingredients in your compost, the more the better, as it creates a richer compost in the end. There are many ingredients that can be composted, that gardeners aren’t aware of, and there are certain ingredients that should never be put into a compost bin.
Here’s a list of what materials should and shouldn’t place in your your compost bin:
What You Can Put Into Your Compost
- Garden prunings (break down faster if mulched or mowed over with lawnmower first)
- Lawn clippings (use thin layers)
- Garden waste
- Mulched woody branches
- Straw mulch materials such as hay, lucerne, pea straw, sugarcane mulch, etc.
- Leaves (break down faster if mulched or mowed over with lawnmower first)
- Pine needles (these break down very slowly and make the compost more acidic, great for acid-loving plants such as blueberries)
- Cut flowers
- Kitchen scraps (fruits and vegetables)
- Breads, cereals, rice, flour
- Coffee grounds and tea bags (not the plastic tea bags)
- Egg shells (crushed)
- Bamboo skewers, wooden chopsticks, toothpicks (chop into smaller pieces with pruning secateurs)
- Vegetarian animal manures (chicken, sheep, cow, rabbit manure, etc)
- Pet hair and feathers
- Newspaper
- Cardboard and egg cartons
- Brown paper bags
- Unbleached non-glossy paper
- Saw dust and wood shavings (small amounts, best to leave them to weather outdoors first outside to leach away the oils and darken)
- Wood ashes (small amounts only as a source of potassium, otherwise they make the compost too alkaline)
- Natural fibres such as cotton, wool, leather, etc (only break down in a fast 18-day hot compost system, don’t break down easily in regular compost)
Hot Composting vs Cold Composting
While it is possible to compost things made of natural fabrics, even leather, this should only be attempted when using a fast and hot composting process such as the Berkeley Hot Composting Method.
Hot composting done properly (not being allowed to cool down until it’s finished!) will get very hot, around 55-65 degrees Celsius (131-149 degree Fahrenheit), and stay that hot continuously for over two weeks, which literally cooks everything, and produces very fine compost in 18 days.
Hot composting will effectively destroy disease pathogens (such as powdery mildew on pumpkin leaves), weed seeds, weed roots (such as couch and kikuyu) and weeds which reproduce through root bulbs (such as oxalis). Some farmers who use the hot compost method even put fresh animal roadkill into the middle of their hot compost heaps because they are rich in nitrogen, and they find nothing but clean bones when the compost is ready. Not a good idea for urban areas though!
The slower, cold composting methods take anywhere from three months to a year, will NOT kill disease pathogens or weed seeds and roots, and produce a coarser compost. Being a slower and less efficient process, cold composting is unsuitable for composting natural fibre fabrics.
What You Should Not Put Into Your Compost
- Diseased plants (can cause diseases to spread in the garden)
- Noxious weeds which regrow from cuttings, seeds or roots
- Pet poo from non-vegetarian animals (contain many pathogens which are a health hazard and can cause diseases)
- Fish and meat scraps, fats, or foods containing these (will rot, smell unpleasant and attract pests such as rodents)
- Dairy products (will rot, smell unpleasant and attract pests such as rodents)
- Cooking oil
- Glossy or coated paper, eg. magazines (contain toxic chemicals)
- Bleached paper, eg. office paper (contain toxic chlorine-based chemicals which shouldn’t be composted)
- Sales receipts and thermal paper (contain a mix of toxic chemicals which shouldn’t be composted)
- Sticky labels, such as the ones on produce and packaging (are made of plastic and/or contain toxic chemicals in the glue)
- Vacuum cleaner dust and dryer lint (once recommended, but now contain too many synthetic fibres which don’t break down)
- Ashes from coal/ barbecue briquettes (contain toxic chemicals)
- Treated wood pieces or sawdust (contain highly toxic copper, chromium and arsenic which will contaminate soil)
- Personal hygiene products, such as tissues, tampons (unhygienic, health hazard)
- Plants treated with toxic pesticides and herbicides (will contaminate compost, soil and food with toxic chemicals)
- Large branches (unless they are mulched first)
- Citrus peels and onions (can use in very small amounts, too much and they can kill the compost bacteria)
Should You Add Lime to Your Compost?
Many composting instructions recommend adding lime (gardening lime, limestone, calcium carbonate) to the compost bin, especially if it becomes a bit too acidic and ‘sours’, as the lime ‘sweetens’ it by reducing acidity.
Don’t add lime, as it will make the compost more alkaline, this will slow down the composting process, as compost microorganisms operate best under a pH range of 5.5 to 8, and ideally prefer a neutral to acidic environment, as acidic conditions are favourable for the growth of fungi and the breakdown of lignin in woody materials and cellulose which is the main compound which makes up plant cell walls.
The other problem with making compost more alkaline is that it causes ammonium nitrogen (NH4+) to be lost to the atmosphere as ammonia gas (NH3). This depletes the compost of its nitrogen, a valuable nutrient for plant growth.
Rather than add lime, it’s easier to simply aerate and mix a compost pile that has become anaerobic and too acidic, this will reduce the acidity.
During the composting process, organic acids are produced at the beginning of the composting process, and later in the process become neutralised. Depending on the ingredients used and the composting process used (slow or fast), mature compost will generally have compost a pH between 6 and 8.
By using the right ingredients in a compost pile, in the correct proportions, it’s easy to create an ongoing supply of nutrient rich compost to improve soil structure and fertility. There’s a little bit of an art to composting, so it pays to experiment a little and find what works best!
Ive been composting for years mostly as a way of managing household
produce scraps. I never really get compost. The scraps disappear but I think Im feeding the neighborhood raccoons. I have two questions. First, is it hopeless if brown stuff is in short supply? All I really have access to are dried leaves and by late winter my stash is gone. The only other thing I have in large quantities are newspapers. I can shred these but are they safe for compost? Second, I cant figure out how to layer. All compost instructions say to layer but I have vegetable scraps daily and I have to mix them in or the whole piles stinks. How does one layer under these circumstances? I cant think of a way of holding the scraps until I have enough brown stuff to layer.
Hi Alex, if you’re not adding the brown dry materials which are high in carbon you won’t get much compost. You can gather huge amounts of dried leaves in autumn, a second compost bin or bay to just pile leaves in when they’re available would help if you have the space. Newspapers work beautifully as long as you don’t use the glossy pages and the glossy magazine inserts that they sometimes come with. The dyes used in newspapers are vegetable dyes, so they’re fine to use.
Layering is easy if you have sufficient composting materials, use alternating 5cm (2″) layer of green and brown ingredients. Remember, use two buckets of dry brown materials for each bucket of green, wet materials. The dry stuff packs down easily when wet.
The alternative to layering is to simply put whatever kitchen scraps you have straight into the compost bin anytime, but for the carbon-rich ingredients you take whole newspaper sheets that have been scrunched up into tight balls and mix them into the compost. They absorb the excess moisture from kitchen scraps and aerate the compost really well. The easiest way to mix compost is with those large corkscrew shaped composting tools which cost around $20, they make the job extremely easy, mixing once a week stops the compost smelling and you end up with compost much faster.
I think I’ll write some more articles on slow cold composting and how to make it work, solve the problems, etc. Stay tuned!
Compost bins are better at processing garden waste, whereas worm farms are far superior for processing straight kitchen scraps. I have three of each in my garden!
Hope this helps.
Good Blog, I was going to suggest to Alex raising Earthworms as well. I’ve had a worm farm for 5+ years, they devour all of our kitchen waste and provide free organic fertilizer, that can’t be beat. Thanks.
Agreed, the rate at which they devour kitchen scraps is phenomenal, no dry carbon-rich materials required and they also produce worm castings which are the best fertiliser available!
Regarding your reply above, re vermicomposting: You state that “no dry carbon-rich materials [are] requred”. This statement is not consistent with my own experience, and also directly contradicted by scholarly literature on C:N ratios for vermicomposting . Can you provide an authoritative citation for this claim?
The optimum C:N ratios for vermicomposting don’t differ much from the figures you give for traditional composting (25:1 – 30:1). One well known study investigating this [1], gives an optimum vermicomposting C:N ratio of about 40:1, i.e. even higher carbon fraction than the traditional-method figures that you quote.
It wasn’t clear if the word “dry” in your response was meant to be a key qualifying conditional, but certainly dry carbon-rich materials, such as cardboard and sawdust, are among the most highly recommended bedding materials for redworms. See the table in [2]. You can’t just feed composting worms pure green (nitrogen-rich) materials (e.g. “kitchen scraps”) alone, as your statement seems to imply. They absolutely need a high carbon bedding environment, and that carbon is an essential component of their diet.
In short, I think your statement is misleading to readers, and for the sake of accuracy, should either be retracted or, if you believe it to be correct, substantiated with an authoritative reference that explains what you might have meant. It does not seem to make sense as written.
Thank you,
Robert
[1] B. Ravindren, et. al, “Bio-optimization of the carbon-to-nitrogen ratio for efficient vermicomposting of chicken manure and waste paper using Eisenia fetida” , https://link.springer.com/article/10.1007/s11356-016-6873-0
[2] G. Munroe, Organic Agriculture Centre of Canada, “Manual of On-Farm Vermicomposting and Vermiculture”, https://d1wqtxts1xzle7.cloudfront.net/31642564/vermiculture_farmersmanual_gm.pdf?1375105512
Hi Robert, thanks for your comments.
I had a look at the references you provided, and i believe you are mistaken in your assumptions, as the information contained in them confirms what I’ve already stated in all my articles on this site. I do research all my material!
In the first reference, they are discussing two separate processes, first a 20 day hot composting process (you can find instructions for an 18-day hot compost process here on this site – https://deepgreenpermaculture.com/diy-instructions/hot-compost-composting-in-18-days/), after which they feed the completed compost to the worms to make worm castings. Not sure if you read through that paper thoroughly, here is a direct quote:
“The study involved a composting stage for 20 days followed by vermicomposting with Eisenia fetida for 7 weeks. The results revealed that 20 days of composting considerably degraded the organic waste mixtures from all treatments and a further 7 weeks of vermiculture significantly improved the bioconversion and nutrient value of all treatments.”
Looking at the second reference, the only mention of high carbon materials and C:N ratios was in respect to bedding materials, they’re always high carbon materials so they don’t rot too fast like the materials fed to the worms.
You might find the following article helpful: Gardening Questions #005 Can You Put Earthworms in the Compost Bin? https://deepgreenpermaculture.com/2021/01/18/gardening-questions-005-can-you-put-earthworms-in-the-compost-bin/
Hope this helps! 🙂
Thank you for your responses! Very helpful. I will certainly try the newspaper balls. As for worms, I’ve read that the worms that are purchased to get started are not native and therefore not good to introduce to a garden. I’m in the U.S. and I know plenty of people do it but this does give me pause.
I just did a quick search to see if I could find the source of this concern. It seems to have discussed but as far as my cursory scan revealed, there is no science to suggest that there is a problem once they are introduced into the garden with the compost they’ve generated. I’ll search a bit more but this is reassuring. Again, thank you both for your help.
Compost worms won’t survive very long in a garden the soil over summer, they can’t escape the heat as they’re surface feeders which need large amounts of compost to live underneath and don’t burrow deeply like earthworms. I mention this in my article on worm farming.
I recently compiled a hot compost pile after reading your previous post, but i did not get it 1.5m high, just half of that maybe. I was really happy when i did my first turn yesterday seeing it went steamy and about 50 degrees hot – I used a soil thermometer. Problem is I won’t have time to do my second turn until next Saturday. Will it be okay if I don’t turn every 2 days as you said? I am worried temperature will be too high killing off the composting bacteria.
Another question is I had put in zucchini leaves which have mildew, and kikuyu/couch roots, as well as seeds in the compost pile. After reading this article about “what not to put in”, I am now worried I have made a big mistake.
Thanks for your comments Lily. When doing an 18 day hot compost using the Berkeley system, with a smaller hot compost heap you run the risk of having it cool down faster, especially in the cooler seasons.
Also, without continuous turning, you also run the risk of your compost cooling down. It needs to stay hot, 55-65 degrees Celsius for around 18 days to kill any pathogens on diseased plants and to destroy any weed seeds, roots and bulbs.
The thermophilic (heat-loving) bacteria won’t get killed by the high temperatures if you don’t tun your compost, but they will use up all the materials in the middle of the compost heap where it’s the hottest, and the available oxygen, then the composting process will slow down or stop, and the outer layers won’t get a chance to compost by taking their turn in the middle of the compost heap which is where they end up after turning. That’s why the turning of the compost every second day is critical when doing a fast hot compost process.
If your hot compost cools down too much from not turning it often enough, add more nitrogen rich material such as blood & bone or manure to kickstart the whole process off once again.
In hot composting, the reason for keeping the compost hot and turning it often is to heat all parts of the compost evenly and regularly to heat pasteurize (basically cook) such things as the zucchini leaves which powdery mildew, couch/kikuyu roots and weed seeds in your composting ingredients. I’ll update the article to note that successful hot composting will kill pathogens, weed seeds, etc. The good thing about hot composting is that if you don’t get it right the first time, you just add more ingredients to the existing ones, and start it again to cook everything nicely! ?
Thanks for the detailed explanation of whats happening in the hot compost pile, now I understand it better. I am now not in a speedy mode as I can let things lie around for ages, just waiting fore whenever I have time and the right mood to go forward lol. But as you said, when the pile cools down, I will add more ingredients to get it going again, making sure the pathogens and weeds got dealt with. Also, I got a cubic of free wood mulch lying in a big pile for months now, can I mix it in as the carbon layer? Alternatively, can I use it as the bottom layer of a no dig bed so as to build height and block off light?
You can add the wood mulch into the compost as the carbon layers, just keep then quite thin as a big thick layer of wood chips doesn’t break down easily.
Whatever you do, don’t put wood mulch underneath a no-dig bed as it takes too long to break down, and will draw too much nitrogen out of the soil through a phenomenon known as nitrogen draw-down.
Can you use it as mulch on top of your garden beds for the warmer seasons? You’d put it on your garden in late spring, November in Australia.
I originally intended to use it as mulch on top of cardboard, which I would lay over my lawn to kill the grass. I would like to eventually rip most of my lawn and turn into an edible garden with fruit trees and perennial vegetables along with annuals, pathway lined by wood mulch. I was inspired after reading your blog on food forest and visiting yours. But having a full time office job, I am slow in action and the wood mulch is turning into a growing mount of knee high kikuyu grass, making it ever harder to deal with. Having said that, I have put in a few make-shift no-dig beds over the back lawn with no permanent structure (because that was meant to be temporary since a bit more than a year ago). I still have to put in on paper where to plant the fruit trees intertwined with annuals and perennials, so as to make it both practical and beautiful, and not costing me much. There is so much to learn, and I am so happy to have found your site, which gave me abundant materials to learn from. Really appreciate your generosity in sharing all these information, and your prompt reply to my questions!
Wondering about the white paper used to wrap deli products, is it OK to put it in the compost bin?
Great information here. Thank you I learned quite a bit. Thank you.
I just started composting a few days ago and and researching the many composting recipes along with learning browns & greens. I have a small area of dirt that I need to remove from around my back door–it is not worthy of using in my garden but should be ok to add to compost. If I sprinkle into compost–is this considered brown or green? Thanks.
You can add soil to your compost in thin layers or you can use it to cover the top of it to keep the heat and moisture in if you’re doing conventional cold composting.
In composting, soil is neither greens or browns, which are ingredients, it’s the finished product! Well, more or less so. Composting is a natural process which occurs on forest floors to create soil. 🙂
Thank you.
We decided to buy a jora composter and wow does it produce compost. It is a tumbler and when we are out of leaves Ill use wood shavings or wood pellets from our local big box home improvement store. We also use shredded papers from our cross cut shredder which also work amazingly well. We struggled for years trying to keep piles turned and in the correct ratios but with the tumbler it is amazingly simple. We also have limited space for composting and wanted something that doesnt smell or attract critters. We are churning out enough compost every four to six weeks to supply our neighbors even in the dead of a Wisconsin winter! Being a hot composter it also handles our fish a meat scraps which is an added bonus. If you struggle like we did with maintaining a compost pile this can really simplify your life like it did ours!
The tumble-bin style compost bins can make life a lot easier if you’re using the slower cold composting process. I have one in my garden, it doesn’t take much effort, a few turns a couple of times a week and you end up with quite nice compost is a much shorter time than if you just let a regular compost bin just sit there. I’ll be writing an article on how to speed up the cold composting process and these bins will definitely rate a mention! Thanks