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How to Compost: Browns & Greens

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.

how to compost - browns and greens

How to compost – browns and greens

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

Robert Pavlis
Editor of GardenMyths.com
I live in southern Ontario, Canada, zone 5 and have been gardening a long time. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

I hope you find Garden Myths an educational site that helps you understand your garden better.

27 Responses to 'How to Compost: Browns & Greens'

  1. jack burton says:

    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.

  2. a says:

    What I am saying is that, given that urine on the ground stinks,
    the sprayed compost would stink even without too-high total N;
    thus a false positive.

  3. a says:

    Superb.

    ——————
    1) Begin to counter repeatedly the simplistic information about
    weed seeds killed by the “heat”.

    ——————
    2) In the article :
    “pee on the compost pile…. If your compost pile starts to stink, you added too much nitrogen.”

    The GROUND stinks for a day or two where I pee ONCE.
    It can happen differently with a compost pile?

    • The two smells may be different. Pee has an odor which depends on things we eat including medicines. When it gets concentrated it does smell more like ammonia which is the same smell you get when there is too much nitrogen in a compost pile.

  4. If I understand this correctly, I can just throw fruit waste which has C:N of 35:1 into a compost bin and it should compost at a very fast rate since it’s very close to the 30:1 ideal ratio, yes?

    I currently compost my food scraps together with pine pellets added to act as the “brown”. If what I read here is true, then I might be able to reduce the pine pellet amount significantly and save money at the same time.

    • If that ratio is correct, then it should compost quickly. But… there are other factors. It is also important to have enough air and fruit waste may clump down and exclude the air needed. It also has a lot of water, maybe too much.

  5. jerrytoo says:

    In my simple mind the 30:1 is a misnomer and the 2″ layer to 6″ layer makes more sense just for the simple reason that it seems to speak in “volumes” of C to N.

    Why not just simplify and come up with a chart of sorts of the various different materials that are available to most home gardens.

    Why not compare the number of cubic ft of Carbon to cubic ft Nitrogen ratio.
    Hence
    The 2″ to 6″ layers mentioned above would, in essence, break down to,, 1cf to 3cf mix.

    That to me would make much better sense than the 30:1 when those numbers mean nothing to me and down right confusing until reading and researching the subject.

    • I did not invent the 30:1 ratio – it is what everyone uses. Lots of sites have lists of common backyard material and their ratio values.

      • jerrytoo says:

        I realized the 30:1 method was the international way long before I even found this site to comment.

        Sorry but I didn’t mean to imply you invented the 30:1 method. I should have stated that I suppose
        .

  6. Maryann Laplaca says:

    I just love your common sense approach and advice. As you say, Mother Nature does it well. Thanks!

  7. Katy Nelson says:

    one benefit of fast composting is that high temperatures kill weed seeds yes?

  8. Marie says:

    OMG Thanks so much for the simplicity of composting on you site. I inherited a 3 bin system in a home we bought last year. I knew enough to add greens and browns + egg shells and coffee grinds but then worried about the right ph as I was ready to feed shrubs and flowers this spring–my only reason for composting actually–I won’t worry so much now. BTW, do I need to sift the compost material (I also inherited a screen which I assume means I should consider sifting the compost before using !)

  9. Ron says:

    Would adding sugar (white, brown, molasses):

    a. hasten the composting process (soil-based)
    b. hasten the fermentation process (bokashi)

    • No. Sugar is like a supper food for bacteria. They grow like crazy on this food source, so you see an explosion of bacteria numbers, and once the sugar is gone thing go back to normal. The excess bacteria die off because of a lack of food. Nothing has really been accomplished.

  10. Don says:

    Good information. I’ve composted for years on a small scale, using a single bin. It wasn’t speedy, but I was in no rush. Occasionally I would have to bag lawn grass, so I added to the compost, and found it did get a bit “high” in smell, but that with some turning/aeration, and leaves, etc. it would get back to normal. Learned by trial and error, but always got batches that I thought must be good for the flower gardens – it just looked and felt like it was a good thing. Then, when the old bin needed replacing, I started doing some research, and designed and built a spiffy three bin facility, with the features I had found lacking in the old bin. When reading about the the proper technique for composting, temperatures, green and brown, etc. I wondered how I had possibly got anything produced in years past, other than through dumb luck – and how fortunate I was not to have permanently scarred and sterilized large sections of our yard, with toxic output from a poor recipe. Slight exaggeration here, as I’ve learned over the years that common sense often trumps information overload [or well intended information beyond my understanding]. However with your information, I will begin my year with the expanded facility, somewhat relieved that I can plod along as before, likely at an increased pace with the luxury of extra bins. Thanks.

    • Keep one thing in mind – mother nature does just fine in the woods with none of this knowledge or a 3 bin system.

      • Don says:

        Mother nature certainly doesn’t need a 3 bin system, but for someone using bins the extra ones do help. I was finding that with a single bin, I was adding material to a batch that was at, or near, a point it could be spread – but I was not ready to unload the bin. Adding new material extended the process. Now I start a new bin, and unload and spread the first bin when the timing is right. Although, I just started last fall, the other advantage was that I found it easier to mix up the material, by transferring one bin to a vacant one with a fork – as opposed to mixing with an aerating tool. I have removable slats in the front of the bins, so it’s quick work to transfer, and the material becomes well mixed and aerated – speeding up the process.

        Thanks again for the series of articles on composting – will be interesting and helpful to a number of gardeners.

        • The 3 bin system works very well, especially if you have removable fronts. The problem for most people is space. the last bins I built had just 3 sides – no front. Not quite as neat looking, but I no longer have to remove the front to work on them.

  11. Very well said – ‘The reality of composting’; why some people are trying to make basic, simple processes look so complicated?

    • There are always cool ways to do things and the reality is that if you follow all the rules you can make compost faster. I’d rather spend my gardening time with plants 🙂

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