The common advice for making compost is that you should use the correct ratio of browns and greens. Why is this important? What is the correct ratio? Are dried green grass clippings, a brown or a green? Good questions that will help you understand how to compost.
Browns and Greens – What are They?
In the simplest form, the terms are quite descriptive. Browns are any plant material that is brown, and includes fall leaves, dried grass, wood products, paper and straw. Greens are – you guessed it- green. It includes fresh grass clippings, freshly picked weeds, plant clippings and most kitchen scraps.
Calling composting ingredients brown or green is useful because it is simple for people to understand. However the terms are not always correct. It would be better to use the terms high nitrogen ingredient, and low nitrogen ingredient. The greens contain higher levels of nitrogen. For example, fresh green plant material contains high levels of nitrogen.
As the greens age they lose nitrogen and turn brown at the same time. Green leaves have high levels of nitrogen, but as they go brown in fall, the nitrogen levels drop. Wood products and straw have low levels of nitrogen.
So is manure a brown or a green? Based on color it is a brown, but based on nitrogen levels it is a green. As far as composting goes, it’s a green.
Other ingredients are also confusing. Alfalfa hay is ‘brown’ in color, but is considered to be a green since it contains a lot of nitrogen.
The bottom line is that the brown and green rule does not always work. Browns can be green, greens can be brown—it’s getting confusing! Stick with me, there is a simple solution.
How to Compost – the C:N Ratio
Recipes for making compost usually tell you to combine the browns and greens in the correct ratios. The recommendations usually go something like this:
The ideal C:N ratio is 30 parts brown to 1 part green.
Or
Use 6 inches browns to 2 inches of greens
Both of these recipes are simple to understand and simple to follow. Both are wrong.
The first one, “The ideal C:N ratio is 30 parts brown to 1 part green”, is just wrong. The author does not understand the term C:N ratio. It is not a ratio of browns to greens. It is a ratio of carbon to nitrogen. The carbon to nitrogen ratio in the compost pile should be 30:1, not the ratio of browns to greens.
The second composting recipe could be correct, but it is probably not. It all depends on which browns and greens you use.
Every ingredient has it’s own C:N ratio. For example horse manure is about 25:1. Fall leaves have a ratio of 30-80:1, depending on age of leaves and type of leaves. Reference 1 has a good list of C:N ratios for common composting ingredients.
The composting recipe of 6” green to 2” brown will only be correct if you use the right combination of ingredients – and that is not likely.
Why is the C:N Ratio Important?
Why is this ratio so important for composting? As discussed in Compost – What is Compost?, composting is a process whereby microbes degrade the organic matter added to the compost pile. These microbes have basic requirements for food, just like you and me. It turns out they grow best when there is a ratio of carbon to nitrogen of about 30:1.
The right amount of carbon and nitrogen makes the microbes happy, and they grow fast. Fast growing microbes means that the composting process happens quickly and the pile heats up to desirable temperatures. So for fast compost it is important to feed the microbes the right ratio of carbon:nitrogen.
What Happens if the C:N Ratio is Wrong?
The microbes will not be as happy, and they won’t decompose the organic material as fast. Composting takes longer and takes place at lower temperatures. However, it does happen.
You do not need the right C:N ratio to make compost. You only need the right ratio if you want to make it quickly!
The Reality of Composting
For the average home owner, it is very difficult to have the right ratio of material. Firstly, how can you figure out if your fall leaves have a ratio of 30:1 or 80:1? You can’t. Secondly, you rarely have the right ingredients available.
Most greens are available in summer. Most browns are available in fall. Some sources recommend holding the browns until you get enough greens and then using them. That is certainly an option, but it is a lot more work, and it needs more space. Who has extra space in their gardens these days?
The reality is that if you simply add your ingredients to the compost pile when you get them, and you turn the pile, you will make compost. It might be a slower process, but that is OK.
Don’t make composting complicated.
How to Make Compost Faster
Most home gardeners have more browns than greens, unless they bring in some manure or have a cow in the back yard. Most of the stuff you collect in fall and spring are browns. Based on the above discussions, too much brown results in a slow composting process. There is a simple solution to this problem.
The problem with too much browns is that the there is not enough nitrogen for all of the carbon. A very simple solution is to add some nitrogen fertilizer to the compost pile. Adding a handful of Urea to a pile of leaves will speed up the process. If you want to go 100% organic, use some fresh chicken manure or you can pee on the compost pile. Both are good organic sources of nitrogen.
If your compost pile starts to stink, you added too much nitrogen. It only takes a bit of Urea.
I stopped worrying about green and brown ratios a long time ago. I still ended up with compost.
References:
1) How to Compost – Carbon to Nitrogen Ratios: http://www.planetnatural.com/composting-101/c-n-ratio/
2) Photo Source: Peter & Ute Grahlmann
Hi Robert. Can you please comment on how the make up of a compost heap helps define its finished NPK values? If I put only fresh grass cuttings in will I end up with finished compost high in nitrogen but low in p and k, for example.
Thanks Chris
No simple answer to that. If you start with high nitrogen, much of it will be lost to the air during the composting process. Resulting in compost that has much less nitrogen than you expect.
High K will also not produce high K compost since it is released quickly and washed out of the compost.
Most commercial compost has a ratio of about 1-1-1. I think most home compost will be close to that even though we all start with different levels.
Very helpful article. Thanks for sharing.
I have one doubt. Dried vegetable peels (cucumber, carrot or potato) are they considered as greens or browns? Can onion and garlic peels be added to compost bin?
They will have higher levels of nitrogen so they care green, but not as green as fresh peels.
There is no reason not to compost onions or garlic.
Never even thought about this. I had a black trash bag that I filled with weeds, roots with some dirt, twigs, dry leaves and after 2 years of it being on my backporch under the sun and rain untouched othet than when I wouldbput stuff in it, I decided this year to finally get rid of it only to find it had turned to perfectly good dirt ❤ I dumped it on one of my garden beds and starting the process again.
good compost.
Yes, the black trash bag method works, I’ve used it on autumn/fall tree leaves, the only draw back is that it is a slow method of composting ie 2 years. To speed things up when I have a massive amount of leaves I use the prior to composting, human urine soaking method in a dustbin/trash/garbage bin, then compost in an aerated bin for 2 to 4 months & have usable compost.
Refer to my Dec 6th 2018 post below for more info on the method Rita
My compost works, but very slowly, as it doesn’t get very hot. Compost is just so useful, so I’d like to speed things up a bit, so I can use it quicker. So after reading this, I will try adding some more nitrogen. Thanks! This information was very informative without making it sound like it’s rocket science requiring expensive tools etc.
Thanks a lot for the information.
I wasnt too worried about the C:N ratio and now I’ll worry even less.
However, I was left wondering: how does one identify that his compost is lacking nitrogen?
Good question. No easy way. If composting is slow, adding more will speed it up. Adding too much will make it smell like urine.
Even with too little nitrogen, it will compost, so maybe the best approach is not to worry about it.
This is the most helpful thing I have read. We are new to this and all the ratios and percentages are a bit confusing and overwhelming. Thanks!
Does drying out used coffee grinds turn it from nitrogen to carbon?
Never. nitrogen and carbon are both elements, and they can’t be turned into anything else.
I love your posts and I believe I’ve read all of them. I love them especially when they validate something I’ve done lately but I’m not sure it makes sense. I have a bounty of leaves in the fall. I collect and shred them with my weedeater then throw them in a bin. I never have enough greens but I have some urea (46-0-0) and I throw a handful on top of the leaves every few inches, then water. This seems to work as within a few days my compost gets up to 160 or even 170 (if it gets this hot I have to aerate to cool it a bit). I’m not satisfied when I do something and I THINK it works, when I just might be wasting my time, but in this post you confirm that Urea does work as a “green” component in compost. I’m cheap and lazy so I’m always checking to ensure that I’m not wasting my time. You’re my “go-to-first” site to check. Thank you.
Thanks a lot. Urea is one of the cheapest sources of nitrogen and just as good as any other source, except, that it will vaporize into the air. Provided it gets into solution, it is fine, but a a dry pellet it will slowly evaporate. It can also burn lawns if you use too much.
I have been soaking dry brown tree leaves in a dustbin (outdoor size trash can) in human urine (see my original post below). I leave them soaking until they are soft & subtle & have absorb the human urine (ie free nitrogen), which compensates for the lack of greens I can supply when I have an absolute abundance of browns (ie brown dry tree leaves). When the browns have absorbed enough urine I add them to the compost bin, with (an optional) sprinkling of blood & bone, & a handful of chicken compost between the layers say every 6 inches, & have found this works fine, I also find I can make quicker compost by placing the compost bin/S (I have 6) in the sun, which means moving them so they get the winter sun, & move them again to get the summer sun.
Note: to Robert I was unable to look at the Facebook page you mentioned as I don’t belong to Facebook so appreciate the answers on your website. Also the other day I wanted to post a question about Long Stem planting, but cannot find where to click to start a new question on your website, would be grateful if you could let me know how to post a new question?
Regards & all the best from Jo (Perth WA Australia)
This website is a blog, and not designed to allow new questions.
I have gutless low nutrient sandy soil, when planting new tree & shrubs can I dig homemade compost (mostly made from leaves & human urine) into the soil that will be in contact with the roots of the new trees & shrubs. A friend has said this homemade compost/leaf mold will burn the roots of the new trees & shrubs if it touches the roots at the time of planting??? Everyone’s thoughts & expert advice appreciated and read.
There are times to break good rules. The rule is not to amend the hole when planting. In really bad sandy soil it might be good to break the rule.
Will compost burn roots? Depends on how fresh it is and what went into making it. If it is made from yard waste, ie mostly plants I doubt it would burn the roots.
I am going to post on the FaceBook group to see the opinions of others.
I’ve been composting for quite a number of years. With 25 mature trees in the yard I never suffer from lack of browns each fall. The leaves range thru apple, ash, maple, pine needles, and some other trees that look nice but I have no clue.
I pack as many leaves as I can into a 4X4X4 wire bin. I layer every six inches or so with about two inches of free coffee grounds from Starbucks. I also add all the garden remains mixed in. I really, really compress those leaves down, even standing on them and jumping up and down. I don’t worry about anaerobic composting as it has enough oxygen mixed in to get started before the winter comes in. In the two months that it has to work before the snows come it decreases in mass by about 20 percent.
We save up all of our kitchen refuse over the winter out on the porch and use it come spring. We fork the whole pile over as soon as it thaws out, and mix the kitchen stuff in. Over the summer we continue to fork and mix kitchen stuff in, along with a healthy amount of human compost activator (urine). By October we have new leaves on the ground and about three good wheelbarrows full of dark black, crumbly compost. It spreads out on the veggie garden to about two inches deep. Come May when we are ready for planting it has disappeared into the soil.
From start to spreading is 12 months and then another six months before we plant in it. Gardening is not for those who want to rush thru life.